Title:
INKJET PRINTHEAD WITH FILTER STRUCTURE AT INLET TO INK CHAMBERS
Kind Code:
A1


Abstract:
An inkjet printhead that has an array of droplet ejectors supported on a printhead integrated circuit (IC). Each of the droplet ejectors has a nozzle aperture and an actuator for ejecting a droplet of ink through the nozzle aperture. Each of the droplet ejectors has a chamber in which the actuator is positioned, the chamber having an inlet for fluid communication with an ink supply. A filter structure in positioned the inlet to inhibit ingress of contaminants into the chamber.



Inventors:
Silverbrook, Kia (Balmain, AU)
Application Number:
12/197304
Publication Date:
12/18/2008
Filing Date:
08/24/2008
Assignee:
Silverbrook Research Pty Ltd
Primary Class:
International Classes:
B21D53/76; B41J2/14; B41J2/04; B41J2/045; B41J2/16; B41J2/175; B41J3/42; B41J3/44; B41J11/00; B41J11/70; B41J15/04; G01D15/00; G06F1/16; G06F21/00; G06K1/12; G06K7/14; G06K19/06; G06K19/073; G07F7/08; G07F7/12; G11B5/127; G11C11/56; H04N1/21; H04N1/32; H04N5/225; H04N5/262; H05K3/20; B41J2/165; H04N1/00
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Primary Examiner:
JACKSON, JUANITA DIONNE
Attorney, Agent or Firm:
SILVERBROOK RESEARCH PTY LTD (BALMAIN, AU)
Claims:
1. An inkjet printhead comprising: an array of droplet ejectors supported on a printhead integrated circuit (IC), each of the droplet ejectors has a nozzle aperture and an actuator for ejecting a droplet of ink through the nozzle aperture and, each of the droplet ejectors has a chamber in which the actuator is positioned, the chamber having an inlet for fluid communication with an ink supply, and a filter structure in the inlet to inhibit ingress of contaminants into the chamber.

2. An inkjet printhead according tot claim 1 wherein the filter structure is a plurality of spaced columns.

3. An inkjet printhead according tot claim 1 wherein the spaced columns each extend generally parallel to the droplet ejection direction.

4. An inkjet printhead according to claim 1 further comprising drive circuitry for providing the actuators with power, the drive circuitry having patterned layers of metal separated by interleaved layers of dielectric material, the layers of metal being interconnected by conductive vias, wherein the drive circuitry has more than two of the metal layers and each of the metal layers are less than 2 microns thick.

5. An inkjet printhead according to claim 4 wherein the metal layers are each less than 1 micron thick.

6. An inkjet printhead according to claim 4 wherein the metal layers are 0.5 microns thick.

7. An inkjet printhead according to claim 1 wherein the array has more than 2000 droplet ejectors.

8. An inkjet printhead according to claim 1 wherein the array has more than 10,000 droplet ejectors.

9. An inkjet printhead according to claim 1 wherein the array has more than 15,000 droplet ejectors.

10. An inkjet printhead according to claim 1 wherein the printhead IC has a printhead surface layer in which the nozzle apertures are formed, the printhead surface layer being less than 10 microns thick.

11. An inkjet printhead according to claim 10 wherein the printhead surface layer is between 1.5 microns and 3.0 microns.

12. An inkjet printhead according to claim 1 wherein each of the droplet ejectors in the array is configured to eject droplets with a volume less than 3 pico-litres each.

13. An inkjet printhead according to claim 12 wherein the droplets ejected have a volume between 1 pico-litre and 2 pico-litres.

14. An inkjet printhead according to claim 1 wherein the array has a nozzle aperture density of more than 100 nozzle apertures per square millimetre and all the nozzle apertures are formed in a printhead surface layer on one face of the printhead IC.

15. An inkjet printhead according to claim 1 wherein the array has a nozzle aperture density of more than 200 nozzle apertures per square millimetre.

16. An inkjet printhead according to claim 1 wherein the array has a nozzle aperture density of more than 300 nozzle apertures per square millimetre.

17. An inkjet printhead according to claim 1 wherein the actuator in each of the droplet ejectors is configured to generate a pressure pulse in a quantity of ink adjacent the nozzle aperture, the pressure pulse being directed towards the nozzles aperture such that the droplet of ink is ejected through the nozzle aperture, the actuator being positioned in the droplet ejector such that it is less than 30 microns from an exterior surface of the printhead surface layer.

18. An inkjet printhead according to claim 17 wherein the actuator is positioned in the droplet ejector such that it is less than 20 microns from an exterior surface of the printhead surface layer.

19. An inkjet printhead according to claim 18 wherein the actuator being positioned in the droplet ejector such that it is less than 15 microns from an exterior surface of the printhead surface layer.

20. An inkjet printhead according to claim 1 wherein the nozzle apertures each have an area less than 600 microns squared.

Description:

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation in part of U.S. application Ser. No. 11/525,857 filed 25 Sep. 2006, which is in turn a continuation of U.S. application Ser. No. 11/064,011 filed on Feb. 24, 2005, now issued as U.S. Pat. No. 717,8903 which is a continuation of U.S. application Ser. No. 10/893,380 filed on Jul. 19, 2004, now issued U.S. Pat. No. 6,938,992, which is a continuation of U.S. application Ser. No. 10/307,348 filed on Dec. 2, 2002, now issued as U.S. Pat. No. 6,764,166, which is a continuation of U.S. application Ser. No. 09/113,122 filed on Jul. 10, 1998, now issued as U.S. Pat. No. 6,557,977, the entire contents of which are herein incorporated by reference.

The following Australian provisional patent applications are hereby incorporated by reference. For the purposes of location and identification, US patents/patent applications identified by their US patent/patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patents/patent applications claim the right of priority.

US PATENT/
PATENT APPLICATION
CROSS-REFERENCED(CLAIMING RIGHT
AUSTRALIANOF PRIORITY FROM
PROVISIONAL PATENTAUSTRALIAN PROVISIONALDOCKET
APPLICATION NO.APPLICATION)NO.
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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to ink jet printing and in particular discloses a shape memory alloy ink jet printer.

The present invention further relates to the field of drop on demand ink jet printing.

CO-PENDING APPLICATIONS

The following applications have been filed by the Applicant simultaneously with the present application: The disclosures of these co-pending applications are incorporated herein by reference.

IJ96USIJ97USIJ98USIJ99USIJ100USIJ101USIJ102US
IJ103USIJ104USIJ105USIJ106USIJ108USIJ109USIJ110US
IJ111US

The above applications have been identified by their filing docket number, which will be substituted with the corresponding application number, once assigned.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number of which are presently in use. The known forms of print have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and inkjet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.

In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.

Many different techniques on ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, “Non-Impact Printing: Introduction and Historical Perspective”, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Inkjet printers themselves come in many different types. The utilization of a continuous stream ink in inkjet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous inkjet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)

Piezoelectric inkjet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.

Recently, thermal inkjet printing has become an extremely popular form of inkjet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed inkjet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.

These printheads have nozzle arrays that share a common basic construction. The electrothermal actuators are fabricated on one supporting substrate and the nozzles through which the ink is ejected are formed in a separate substrate or plate. The nozzle plate and thermal actuators are then aligned and assembled. The nozzle plate and the thermal actuator substrate can be sealed together in a variety of different ways, for example, epoxy adhesive, anodic bonding or sealing glass.

Accurate registration between the thermal actuators and the nozzles can be problematic. These problems effectively restrict the size of the nozzle array in any one monolithic plate and corresponding actuator substrate. Any misalignment between the nozzles and the underlying actuators will compound as the dimensions of the array increase. Furthermore, differential thermal expansion between the nozzle plate and the actuator substrate create greater misalignments as the array sizes increase. In light of these registration issues, printhead nozzle arrays have a nozzle densities of the order of 10 to 20 nozzles per square mm and less than about 300 nozzles in any one monolithic plate and corresponding actuator substrate.

Given these limits on nozzle array size, pagewidth printheads using this two-part design are impractical. A stationary printhead extending the printing width of the media substrate would require many separate printhead arrays mounted in precise alignment with each other. The complexity of this arrangement makes such printers commercially unrealistic.

As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high speed operation, safe and continuous long term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides an inkjet printhead comprising:

an array of droplet ejectors supported on a printhead integrated circuit (IC), each of the droplet ejectors has a nozzle aperture and an actuator for ejecting a droplet of ink through the nozzle aperture and, each of the droplet ejectors has a chamber in which the actuator is positioned, the chamber having an inlet for fluid communication with an ink supply, and a filter structure in the inlet to inhibit ingress of contaminants into the chamber.

A filter structure at the inlet to each ink chamber is more likely to remove contaminants than a filter positioned further upstream in the in the ink supply flow. Contaminants, including air bubbles, can originate at all points along the ink supply line, so there is less chance of nozzle clogging or other detrimental effects if the ink flow is filtered at each of the chamber inlets.

In a particularly preferred form, the filter structure is a plurality of spaced columns. In some embodiments, the spaced columns each extend generally parallel to the droplet ejection direction.

Preferably, the printhead IC has drive circuitry for providing the actuators with power, the drive circuitry having patterned layers of metal separated by interleaved layers of dielectric material, the layers of metal being interconnected by conductive vias, wherein the drive circuitry has more than two of the metal layers and each of the metal layers are less than 2 microns thick.

Incorporating the drive circuitry and the droplet ejectors onto the same supporting substrate reduces the number of electrical connections needed on the printhead IC and the resistive losses when transmitting power to the actuators. The circuitry on the printhead IC needs to have more than just power and ground metal layers in order to provide the necessary drive FETs, shift registers and so on. However, each metal layer can be thinner and fabricated using well known and efficient techniques employed in standard semiconductor fabrication. Overall, this yields production efficiencies in time and cost.

Preferably, the metal layers are each less than 1 micron thick. In a still further preferred form, the metal layers are 0.5 microns thick. Half micron CMOS is often used in semiconductor fabrication and is thick enough to ensure that the connections at the bond pads are reliable.

Preferably, the array has a nozzle aperture density of more than 100 nozzle apertures per square millimetre. Preferably, the array has a nozzle aperture density of more than 200 nozzle apertures per square millimetre. In a further preferred form, the array has a nozzle aperture density of more than 300 nozzle apertures per square millimetre.

Forming the nozzle apertures within a layer on one side of the underlying wafer instead of laser ablating nozzles in a separated plate that is subsequently mounted to the printhead integrated circuit significantly improves the accuracy of registration between an actuator and its corresponding nozzle. With more precise registration between the nozzle aperture and the actuator, a greater nozzle density is possible. Nozzle density has a direct bearing on the print resolution and or print speeds. A high density array of nozzles can print to all the addressable locations (the grid of locations on the media substrate at which the printer can print a dot) with less passes of the printhead or ideally, a single pass.

In some embodiments, the array has more than 2000 droplet ejectors. Preferably, the array has more than 10,000 droplet ejectors. In a further preferred form, the array has more than 15,000 droplet ejectors. Increasing the number of nozzles fabricated on a printhead IC allows larger arrays, faster print speeds and ultimately pagewidth printheads.

Preferably, the printhead surface layer is less than 10 microns thick. In a further preferred form, the printhead surface layer is less than 8 microns thick. In a still further preferred form, the printhead surface layer is less than 5 microns thick. In particular embodiments, the printhead surface layer is between 1.5 microns and 3.0 microns.

Forming the nozzle apertures in a thin surface layer reduces stresses caused by differential thermal expansion. Thin surface layers mean that the ‘barrel’ of the nozzle aperture is short and has less fluidic drag on the droplets as they are ejected. This reduces the ejection energy that the actuator needs to impart to the ink which in turn reduces the energy needed to be input into the actuator. With the actuators operating at lower power, they can be placed closer together on the printhead IC because there is less cross talk between nozzles and less excess heat generated. The close spacing increases the density of droplet ejectors within the array.

Preferably, each of the droplet ejectors in the array is configured to eject droplets with a volume less than 3 pico-litres each. In a further preferred form, each of the droplet ejectors in the array is configured to eject droplets with a volume less than 2 pico-litres each. In a particularly preferred form, the droplets ejected have a volume between 1 pico-litre and 2 pico-litres.

Configuring the ejector so that it ejects small volume drops reduces the energy needed to eject drops.

Preferably, the actuator in each of the droplet ejectors is configured to generate a pressure pulse in a quantity of ink adjacent the nozzle aperture, the pressure pulse being directed towards the nozzles aperture such that the droplet of ink is ejected through the nozzle aperture, the actuator being positioned in the droplet ejector such that it is less than 30 microns from an exterior surface of the printhead surface layer. Preferably, the actuator is positioned in the droplet ejector such that it is less than 20 microns from an exterior surface of the printhead surface layer. In a further preferred form, the actuator being positioned in the droplet ejector such that it is less than 15 microns from an exterior surface of the printhead surface layer.

In some preferred embodiments, the nozzle apertures each have an area less than 600 microns squared. In a further preferred form, the nozzle apertures each have an area less than 400 microns squared. In a particularly preferred form, the nozzle apertures each have an area between 150 microns squared and 200 microns squared.

Preferably, during printing 100% coverage at full print rate, each of the actuators has an average power consumption less than 1.5 mW. In a further preferred form, the average power consumption is between 0.5 mW and 1.0 mW. In a still further preferred form, the array has more than 15,000 of the droplet ejectors and operates at less than 10 Watts during printing 100% coverage at full print rate. Configuring the actuators for low power ejection causes less cross talk between nozzles and less, if any, excess heat generation. As a result, the density of the droplet ejectors on the printhead IC can increase. Droplet ejector density has a direct bearing on the print resolution and or print speeds. A high density array of nozzles can print to all the addressable locations (the grid of locations on the media substrate at which the printer can print a dot) with less passes of the printhead or ideally, a single pass, as is the case with a pagewidth printhead.

Preferably, each of the actuators is configured to consume less than 1 Watt during activation. In a further preferred form, each of the actuators is configured to consume less than 500 mW during activation. In some embodiments, each of the actuators is configured to consume between 100 mW and 500 mW during activation.

Preferably, the array of droplet ejectors is arranged as a plurality of rows of the droplet ejectors, the inkjet printhead further comprising an ink supply channel extending parallel to the plurality of rows, and an inlet conduit extending from the supply channel to an opposing surface of the printhead IC. Preferably, the supply channel extends between at least two of the plurality of rows. Feeding ink to the rows of droplet ejectors via a parallel supply channel that has a supply conduit to the ‘back’ of the IC, reduces the number of deep anisotropic back etches. Less back etching preserves the structural integrity of the printhead IC which is more robust and less likely to be damaged by die handling equipment.

Preferably, the droplet ejectors are configured to eject ink droplets at a velocity less than 4.5 m/s. In a further preferred form, the velocity is less than 4.0 m/s. The Applicant's work has found drop ejection velocities greater than 4.5 m/s have significantly more satellite drops. Furthermore, tests show a velocity less than 4.0 m/s have negligible satellite drops.

Preferably, each of the droplet ejectors has a chamber in which the actuator is positioned, the chamber having a volume less than 30,000 microns cubed. In a further preferred form, the volume is less than 25,000 microns cubed. Low energy ejection of ink droplets generates little, if any, excess heat in the printhead. A build up of excess heat in the printhead imposes a limit on the nozzle firing frequency and thereby limits the print speed. The IJ30 printhead is self cooling (the heat generated by the thermal actuator is removed from the printhead with the ejected drop). In this case, the print speed is only limited by the rate at which the ink can be supplied to the printhead or the speed that the media substrate can be fed past the printhead. Reducing the volume of the ink chambers reduces the volume of ink in which the heat can dissipate. However, a reduced volume ink chamber has a fast refill time and relies solely on capillary action. As the actuator is configured for low energy input, the reduced volume of ink does not cause problems for heat dissipation.

Preferably, the printhead IC has a back face that is opposite said one face on which the printhead surface layer is formed, and at least one supply conduit extending from the back face to the array of droplet ejectors such that the at least one supply conduit is in fluid communication with a plurality of the droplet ejectors in the array. In a further preferred form, the printhead IC has a plurality of the supply conduits and drive circuitry for providing the actuators with power, the drive circuitry having patterned layers of metal separated by interleaved layers of dielectric material, the layers of metal being interconnected by conductive vias, wherein the drive circuitry extends between the plurality of supply conduits. Supplying the array of droplet ejectors with ink from the back face of the printhead IC instead of along the front face provides more room to the electrical contacts and drive circuitry. This in turn, provides the scope to increase the density of droplet ejectors per unit area on the printhead IC.

Preferably, the array of droplet ejectors is arranged as a plurality of rows of the droplet ejectors, the printhead IC further comprises an ink supply channel extending parallel to the plurality of rows, such that the ink supply channel connects to the plurality of supply conduits extending from the back face of the printhead IC. Preferably, the supply channel extends between at least two of the plurality of rows. In a particularly preferred form, the printhead IC has an elongate configuration with its longitudinal extent parallel to the rows of droplet ejectors, the printhead IC further comprising a series of electrical contacts along of its longitudinal sides for receiving power and print data for all the droplet ejectors in the array.

According to a second aspect, the present invention provides a method of fabricating an inkjet printhead comprising the steps of:

forming a plurality of actuators on a monolithic substrate;

covering the actuators with a sacrificial material;

covering the sacrificial material with a printhead surface layer;

defining a plurality of nozzle apertures in the printhead surface layer such that each of the actuators corresponds to one of the nozzle apertures; and,

removing at least some of the sacrificial material on each of the actuators through the nozzle aperture corresponding to each of the actuators.

By forming the nozzle apertures in a printhead surface layer that is a lithographically deposited structure on the monolithic substrate, the alignment with the actuators is within tolerances while fabrication remains cost effective. Greater precision allows the printhead to have a higher nozzle density and the array can be larger before CTE mismatch causes the nozzle to actuator alignment to exceed the required tolerances.

Preferably, the method further comprises the step of supporting the actuators on the monolithic substrate by CMOS drive circuitry positioned between the monolithic substrate and the actuators and the monolithic substrate. Preferably, the method further comprises the step of depositing a protective layer over the CMOS drive circuitry and etching the protective layer to expose areas of the CMOS drive circuitry configured to be electrical contacts for the actuators. Preferably, the protective layer is a nitride material. Silicon nitride is particularly suitable.

Preferably, the method further comprises the step of forming etchant holes in the printhead surface layer for exposing the sacrificial material beneath the printhead surface layer to etchant, the etchant holes being smaller than the nozzle apertures such that during printer operation, ink is not ejected through the etchant holes.

Preferably, the printhead surface layer is a nitride material deposited over a sacrificial layer. In a further preferred form, the printhead surface layer is silicon nitride. Preferably, the monolithic substrate has an ink ejection side providing a planar support surface for the CMOS drive circuitry and the plurality of actuators, the monolithic substrate also having an ink supply surface opposing the ink ejection side, the printhead surface layer has a roof layer extending in a plane parallel to the planar support surface, and side wall structures formed integrally with the roof layer and extending toward the planar support surface. Preferably, the printhead surface layer has a plurality of filter structures formed integrally with the roof layer and positioned to filter ink flow to each of the actuators respectively. Preferably, the method further comprises the step of etching ink supply channels from the ink supply surface of the monolithic substrate to the planar support surface of the ink ejection side. In a further preferred form, the step of removing at least some of the sacrificial material on each of the actuators through the nozzle apertures is performed after the ink supply channels are etched from the ink supply surface.

According to a third aspect, the present invention provides an inkjet printer comprising:

a printhead mounted adjacent a media feed path;

an array of droplet ejectors for ejecting ink droplets on to a media substrate, each of the droplet ejectors having an electro-thermal actuator; and,

a media feed drive for moving the media substrate relative to the array of droplet ejectors at a speed greater than 0.1 m/s.

Increasing the speed of the media substrate relative to the printhead, whether the printhead is a scanning or pagewidth type, reduces the time needed to complete printjobs.

Preferably, the media feed drive is configured for moving the media substrate relative to the array of droplet ejectors at a speed greater than 0.15 m/s.

The nozzle chamber structure may be defined by the substrate as a result of an etching process carried out on the substrate, such that one of the layers of the substrate defines the ejection port on one side of the substrate and the actuator is positioned on an opposite side of the substrate.

According to a fourth aspect of the present invention there is provided a method of ejecting ink from a chamber comprising the steps of: a) providing a cantilevered beam actuator incorporating a shape memory alloy; and b) transforming said shape memory alloy from its martensitic phase to its austenitic phase or vice versa to cause the ink to eject from said chamber. Further, the actuator comprises a conductive shape memory alloy panel in a quiescent state and which transfers to an ink ejection state upon heating thereby causing said ink ejection from the chamber. Preferably, the heating occurs by means of passing a current through the shape memory alloy. The chamber is formed from a crystallographic etch of a silicon wafer so as to have one surface of the chamber substantially formed by the actuator. Advantageously, the actuator is formed from a conductive shape memory alloy arranged in a serpentine form and is attached to one wall of the chamber opposite a nozzle port from which ink is ejected. Further, the nozzle port is formed by the back etching of a silicon wafer to the epitaxial layer and etching a nozzle port hole in the epitaxial layer. The crystallographic etch includes providing side wall slots of non-etched layers of a processed silicon wafer so as to extend the dimensions of the chamber as a result of the crystallographic etch process. Preferably, the shape memory alloy comprises nickel titanium alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings which:

FIG. 1 is an exploded perspective view of a single ink jet nozzle as constructed in accordance with one embodiment;

FIG. 2 is a top cross sectional view of a single ink jet nozzle in its quiescent state taken along line A-A in FIG. 1;

FIG. 3 is a top cross sectional view of a single ink jet nozzle in its actuated state taken along line A-A in FIG. 1;

FIG. 4 provides a legend of the materials indicated in FIGS. 5 to 15;

FIG. 5 to FIG. 15 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle;

FIG. 16 is a schematic cross-sectional view of a single ink jet nozzle constructed in accordance with another embodiment;

FIG. 17 is a schematic cross-sectional view of a single ink jet nozzle constructed in accordance with a preferred embodiment, with the thermal actuator in its activated state;

FIG. 18 is a schematic diagram of the conductive layer utilized in the thermal actuator of the ink jet nozzle constructed in accordance with a preferred embodiment;

FIG. 19 is a close-up perspective view of portion A of FIG. 18;

FIG. 20 is a cross-sectional schematic diagram illustrating the construction of a corrugated conductive layer in accordance with a preferred embodiment of the present invention;

FIG. 21 is a schematic cross-sectional diagram illustrating the development of a resist material through a half-toned mask utilized in the fabrication of a single ink jet nozzle in accordance with a preferred embodiment;

FIG. 22 is an exploded perspective view illustrating the construction of a single ink jet nozzle in accordance with a preferred embodiment;

FIG. 23 is a perspective view of a section of an ink jet printhead configuration utilizing ink jet nozzles constructed in accordance with a preferred embodiment.

FIG. 24 provides a legend of the materials indicated in FIGS. 25 to 38; and,

FIG. 25 to FIG. 38 illustrate sectional views of the manufacturing steps in one form of construction of an ink jet printhead nozzle.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

IJ26

The embodiment shown in FIGS. 1 to 15 is referred to by the Applicant and within the Assignee company, as the IJ26 printhead. In this printhead, shape memory materials are utilized to construct an actuator suitable for injecting ink from the nozzle of an ink chamber.

FIG. 1 illustrates an exploded perspective view 10 of a single ink jet nozzle as constructed in accordance with the preferred embodiment. The ink jet nozzle 10 is constructed from a silicon wafer base utilizing back etching of the wafer to a boron doped epitaxial layer. Hence, the ink jet nozzle 10 comprises a lower layer 11 which is constructed from boron doped silicon. The boron doped silicon layer is also utilized a crystallographic etch stop layer. The next layer comprises the silicon layer 12 that includes a crystallographic pit 13 having side walls etched at the usual angle of 54.74 degrees. The layer 12 also includes the various required circuitry and transistors for example, CMOS layer (not shown). After this, a 0.5 micron thick thermal silicon oxide layer 15 is grown on top of the silicon wafer 12.

After this comes various layers which can comprise a two level metal CMOS process layers which provide the metal interconnect for the CMOS transistors formed within the layer 12. The various metal pathways etc. are not shown in FIG. 1 but for two metal interconnects 18, 19 which provide interconnection between a shape memory alloy layer 20 and the CMOS metal layers 16. The shape memory metal layer is next and is shaped in the form of a serpentine coil to be heated by end interconnect/via portions 21, 23. A top nitride layer 22 is provided for overall passivation and protection of lower layers in addition to providing a means of inducing tensile stress to curl upwards the shape memory alloy layer 20 in its quiescent state.

The preferred embodiment relies upon the thermal transition of a shape memory alloy 20 (SMA) from its martensitic phase to its austenitic phase. The basis of a shape memory effect is a martensitic transformation which creates a polydemane phase upon cooling. This polydemane phase accommodates finite reversible mechanical deformations without significant changes in the mechanical self energy of the system. Hence, upon re-transformation to the austenitic state the system returns to its former macroscopic state to displaying the well known mechanical memory. The thermal transition is achieved by passing an electrical current through the SMA. The actuator layer 20 is suspended at the entrance to a nozzle chamber connected via leads 18, 19 to the lower layers.

In FIG. 2, there is shown a cross-section of a single nozzle 10 when in its quiescent state, the section basically being taken through the line A-A of FIG. 1. The actuator 30 is bent away from the nozzle when in its quiescent state. In FIG. 3, there is shown a corresponding cross-section for a single nozzle 10 when in an actuated state. When energized, the actuator 30 straightens, with the corresponding result that the ink is pushed out of the nozzle. The process of energizing the actuator 30 requires supplying enough energy to raise the SMA above its transition temperature, and to provide the latent heat of transformation to the SMA 20.

Obviously, the SMA martensitic phase must be pre-stressed to achieve a different shape from the austenitic phase. For printheads with many thousands of nozzles, it is important to achieve this pre-stressing in a bulk manner. This is achieved by depositing the layer of silicon nitride 22 using Plasma Enhanced Chemical Vapour Deposition (PECVD) at around 300° C. over the SMA layer. The deposition occurs while the SMA is in the austenitic shape. After the printhead cools to room temperature the substrate under the SMA bend actuator is removed by chemical etching of a sacrificial substance. The silicon nitride layer 22 is under tensile stress, and causes the actuator to curl upwards. The weak martensitic phase of the SMA provides little resistance to this curl. When the SMA is heated to its austenitic phase, it returns to the flat shape into which it was annealed during the nitride deposition. The transformation being rapid enough to result in the ejection of ink from the nozzle chamber.

There is one SMA bend actuator 30 for each nozzle. One end 31 of the SMA bend actuator is mechanically connected to the substrate. The other end is free to move under the stresses inherent in the layers.

Returning to FIG. 1 the actuator layer is therefore composed of three layers:

1. An SiO2 lower layer 15. This layer acts as a stress ‘reference’ for the nitride tensile layer. It also protects the SMA from the crystallographic silicon etch that forms the nozzle chamber. This layer can be formed as part of the standard CMOS process for the active electronics of the printhead.

2. A SMA heater layer 20. A SMA such as nickel titanium (NiTi) alloy is deposited and etched into a serpentine form to increase the electrical resistance.

3. A silicon nitride top layer 22. This is a thin layer of high stiffness which is deposited using PECVD. The nitride stoichiometry is adjusted to achieve a layer with significant tensile stress at room temperature relative to the SiO2 lower layer. Its purpose is to bend the actuator at the low temperature martensitic phase.

As noted previously the ink jet nozzle of FIG. 1 can be constructed by utilizing a silicon wafer having a buried boron epitaxial layer. The 0.5 micron thick dioxide layer 15 is then formed having side slots 45 which are utilized in a subsequent crystallographic etch. Next, the various CMOS layers 16 are formed including drive and control circuitry (not shown). The SMA layer 20 is then created on top of layers 15/16 and being interconnected with the drive circuitry. Subsequently, a silicon nitride layer 22 is formed on top. Each of the layers 15, 16, 22 include the various slots e.g. 45 which are utilized in a subsequent crystallographic etch. The silicon wafer is subsequently thinned by means of back etching with the etch stop being the boron layer 11. Subsequent boron etching forms the nozzle hole e.g. 47 and rim 46 (FIG. 3). Subsequently, the chamber proper is formed by means of a crystallographic etch with the slots 45 defining the extent of the etch within the silicon oxide layer 12.

A large array of nozzles can be formed on the same wafer which in turn is attached to an ink chamber for filling the nozzle chambers.

One form of detailed manufacturing process which can be used to fabricate monolithic ink jet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

1. Using a double-sided polished wafer deposit 3 microns of epitaxial silicon heavily doped with boron.

2. Deposit 10 microns of epitaxial silicon, either p-type or n-type, depending upon the CMOS process used.

3. Complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, 2 metal CMOS process. This step is shown in FIG. 5. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 4 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

4. Etch the CMOS oxide layers down to silicon or aluminum using Mask 1. This mask defines the nozzle chamber, and the edges of the printheads chips. This step is shown in FIG. 6.

5. Crystallographically etch the exposed silicon using, for example, KOH or EDP (ethylenediamine pyrocatechol). This etch stops on <111> crystallographic planes, and on the boron doped silicon buried layer. This step is shown in FIG. 7.

6. Deposit 12 microns of sacrificial material. Planarize down to oxide using CMP. The sacrificial material temporarily fills the nozzle cavity. This step is shown in FIG. 8.

7. Deposit 0.1 microns of high stress silicon nitride (Si3N4).

8. Etch the nitride layer using Mask 2. This mask defines the contact vias from the shape memory heater to the second-level metal contacts.

9. Deposit a seed layer.

10. Spin on 2 microns of resist, expose with Mask 3, and develop. This mask defines the shape memory wire embedded in the paddle. The resist acts as an electroplating mold. This step is shown in FIG. 9.

11. Electroplate 1 micron of Nitinol. Nitinol is a ‘shape memory’ alloy of nickel and titanium, developed at the Naval Ordnance Laboratory in the US (hence Ni—Ti-NOL). A shape memory alloy can be thermally switched between its weak martensitic state and its high stiffness austenitic state.

12. Strip the resist and etch the exposed seed layer. This step is shown in FIG. 10.

13. Wafer probe. All electrical connections are complete at this point, bond pads are accessible, and the chips are not yet separated.

14. Deposit 0.1 microns of high stress silicon nitride. High stress nitride is used so that once the sacrificial material is etched, and the paddle is released, the stress in the nitride layer will bend the relatively weak martensitic phase of the shape memory alloy. As the shape memory alloy—in its austenitic phase—is flat when it is annealed by the relatively high temperature deposition of this silicon nitride layer, it will return to this flat state when electrothermally heated.

15. Mount the wafer on a glass blank and back-etch the wafer using KOH with no mask. This etch thins the wafer and stops at the buried boron doped silicon layer. This step is shown in FIG. 11.

16. Plasma back-etch the boron doped silicon layer to a depth of 1 micron using Mask 4. This mask defines the nozzle rim. This step is shown in FIG. 12.

17. Plasma back-etch through the boron doped layer using Mask 5. This mask defines the nozzle, and the edge of the chips. At this stage, the chips are still mounted on the glass blank. This step is shown in FIG. 13.

18. Strip the adhesive layer to detach the chips from the glass blank. Etch the sacrificial layer. This process completely separates the chips. This step is shown in FIG. 14.

19. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply different colors of ink to the appropriate regions of the front surface of the wafer.

20. Connect the printheads to their interconnect systems.

21. Hydrophobize the front surface of the printheads.

22. Fill with ink and test the completed printheads. A filled nozzle is shown in FIG. 15.

IJ30

Another embodiment is shown in FIGS. 16 to 38. The Assignee refers to this embodiment as the IJ30 printhead. This printhead has ink ejection nozzles actuated by means of a thermal actuator which includes a “corrugated” copper heating element encased in a polytetrafluoroethylene (PTFE) layer.

Turning now to FIG. 16, there is illustrated a cross-sectional view of a single inkjet nozzle 110 as constructed in accordance with the present embodiment. The inkjet nozzle 110 includes an ink ejection port 111 for the ejection of ink from a chamber 112 by means of actuation of a thermal paddle actuator 113. The thermal paddle actuator 113 comprises an inner copper heating portion 114 and paddle 115 which are encased in an outer PTFE layer 116. The outer PTFE layer 116 has an extremely high coefficient of thermal expansion (approximately 770×10−6, or around 380 times that of silicon). The PTFE layer 116 is also highly hydrophobic which results in an air bubble 117 being formed under the actuator 113 due to out-gassing etc. The top PTFE layer 61 is treated so as to make it hydrophilic. The heater 114 is also formed within the lower portion 60 of the actuator 113.

The heater 114 is connected at ends 120, 121 (see also FIG. 22) to a lower CMOS drive layer 118 containing drive circuitry (not shown). For the purposes of actuation of actuator 113, a current is passed through the copper heater element 114 which heats the bottom surface of actuator 113. Turning now to FIG. 17, the bottom surface of actuator 113, in contact with air bubble 117 remains heated while any top surface heating is carried away by the exposure of the top surface of actuator 113 to the ink within chamber 112. Hence, the bottom PTFE layer expands more rapidly resulting in a general rapid bending upwards of actuator 113 (as illustrated in FIG. 17) which consequentially causes the ejection of ink from ink ejection port 111. FIG. 17 also shows an air inlet channel 128 formed between two nitride layers 142, 126 such that air is free to flow 129 along channel 128 and through holes, e.g. 125, in accordance with any fluctuating pressure influences. The air flow 129 acts to reduce the vacuum on the back surface of actuator 113 during operation. As a result less energy is required for the movement of the actuator 113.

The actuator 113 can be deactivated by turning off the current to heater element 114. This will result in a return of the actuator 113 to its rest position.

The actuator 113 includes a number of significant features. In FIG. 18 there is illustrated a schematic diagram of the conductive layer of the thermal actuator 113. The conductive layer includes paddle 115, which can be constructed from the same material as heater 114, i.e. copper, and which contains a series of holes e.g. 123. The holes are provided for interconnecting layers of PTFE both above and below panel 115 so as to resist any movement of the PTFE layers past the panel 115 and thereby reducing any opportunities for the delamination of the PTFE and copper layers.

Turning to FIG. 19, there is illustrated a close up view of a portion of the panel 115 indicated as A is FIG. 18 illustrating the corrugated nature 122 of the heater element 114 within the PTFE layers of actuator 113 of FIG. 16. The corrugated nature 122 of the heater 114 allows for a more rapid heating of the portions of the bottom layer surrounding the corrugated heater. Any resistive heater which is based upon applying a current to heat an object will result in a rapid, substantially uniform elevation in temperature of the outer surface of the current carrying conductor. The surrounding PTFE volume is therefore heated by means of thermal conduction from the resistive element. This thermal conduction is known to proceed, to a first approximation, at a substantially linear rate with respect to distance from a resistive element. By utilizing a corrugated resistive element the bottom surface of actuator 113 is more rapidly heated as, on average, a greater volume of the bottom PTFE surface is closer to a portion of the resistive element. Therefore, the utilisation of a corrugated resistive element results in a more rapid heating of the bottom surface layer and therefore a more rapid actuation of the actuator 113. Further, a corrugated heater also assists in resisting any delamination of the copper and PTFE layer.

Turning now to FIG. 20, the corrugated resistive element can be formed by depositing a resist layer 150 on top of the first PTFE layer 151. The resist layer 150 is exposed utilizing a mask 152 having a half-tone pattern delineating the corrugations. After development the resist 150 contains the corrugation pattern. The resist layer 150 and the PTFE layer 151 are then etched utilizing an etchant that erodes the resist layer 150 at substantially the same rate as the PTFE layer 151. This transfers the corrugated pattern into the PTFE layer 151. Turning to FIG. 21, on top of the corrugated PTFE layer 151 is deposited the copper heater layer 114 which takes on a corrugated form in accordance with its under layer. The copper heater layer 114 is then etched in a serpentine or concertina form. Subsequently, a further PTFE layer 153 is deposited on top of layer 114 so as to form the top layer of the thermal actuator 113. Finally, the second PTFE layer 152 is planarized to form the top surface 61 of the thermal actuator 113 (FIG. 16).

Returning again now to FIG. 16, it is noted that an ink supply can be supplied through a throughway for channel 138 which can be constructed by means of deep anisotropic silicon trench etching such as that available from STS Limited (“Advanced Silicon Etching Using High Density Plasmas” by J. K. Bhardwaj, H. Ashraf, page 224 of Volume 2639 of the SPIE Proceedings in Micro Machining and Micro Fabrication Process Technology). The ink supply flows from channel 138 through a grill formed by a series of columns 140 (see also FIG. 22) into chamber 112. The grill columns 140, which can comprise silicon nitride or similar insulating material, act to remove foreign bodies from the ink flow. The grill of columns 140 also helps to pinch the PTFE actuator 113 to a base CMOS layer 118, the pinching providing an important assistance for the thermal actuator 113 so as to ensure a substantially decreased likelihood of the thermal actuator layer 113 separating from a base CMOS layer 118. It will be appreciated that a filter structure at the inlet to each ink chamber is more likely to remove contaminants than a filter positioned further upstream in the in the ink supply flow. Contaminants, including air bubbles, can originate at all points along the ink supply line, so there is less chance of nozzle clogging or other detrimental effects if the ink flow is filtered at each of the chamber inlets.

A series of sacrificial etchant holes, e.g. 119, are provided in the top wall 148 of the chamber 112 to allow sacrificial etchant to enter the chamber 112 during fabrication so as to increase the rate of etching. The small size of the holes, e.g. 119, does not affect the operation of the device 110 substantially as the surface tension across holes, e.g. 119, stops ink being ejected from these holes, whereas, the larger size hole 111 allows for the ejection of ink.

Turning now to FIG. 22, there is illustrated an exploded perspective view of a single nozzle 110. The nozzles 110 can be formed in layers starting with a silicon wafer device 141 having a CMOS layer 118 on top thereof as required. The CMOS layer 118 provides the various drive circuitry for driving the copper heater elements 114.

On top of the CMOS layer 118 a nitride layer 142 is deposited, providing primarily protection for lower layers from corrosion or etching. Next a nitride layer 126 is constructed having the aforementioned holes, e.g. 125, and posts, e.g. 127. The structure of the nitride layer 126 can be formed by first laying down a sacrificial glass layer (not shown) onto which the nitride layer 126 is deposited. The nitride layer 126 includes various features, for example, a lower ridge portion 111 in addition to vias for the subsequent material layers.

In construction of the actuator 113 (FIG. 16), the process of creating a first PTFE layer proceeds by laying down a sacrificial layer on top of layer 126 in which the air bubble underneath actuator 113 subsequently forms. On top of this is formed a first PTFE layer utilizing the relevant mask. Preferably, the PTFE layer includes vias for the subsequent copper interconnections. Next, a copper layer 143 is deposited on top of the first PTFE layer 151 and a subsequent PTFE layer is deposited on top of the copper layer 143, in each case, utilizing the required mask.

The nitride layer 146 can be formed by the utilisation of a sacrificial glass layer which is masked and etched as required to form the side walls and the grill 140. Subsequently, the top nitride layer 148 is deposited again utilizing the appropriate mask having considerable holes as required. Subsequently, the various sacrificial layers can be etched away so as to release the structure of the thermal actuator.

In FIG. 23 there is illustrated a section of an ink jet printhead configuration 190 utilizing ink jet nozzles constructed in accordance with a preferred embodiment, e.g. 191. The configuration 190 can be utilized in a three color process 1600 dpi printhead utilizing 3 sets of 2 rows of nozzle chambers, e.g. 192, 193, which are interconnected to one ink supply channel, e.g. 194, for each set. The three supply channels 194, 195, 196 are interconnected to cyan, magenta and yellow ink reservoirs respectively.

As shown in FIG. 23, nozzle rows 192 and 193 are supplied by the same supply channel 194 and offset from each other in the paper feed direction. As discussed above, the printhead resolution is 1600 dpi and hence the nozzle pitch perpendicular to the paper feed direction is one 1600th of an inch, or 15.875 microns. Accordingly, the nozzles in each row on the printhead are spaced at 31.75 micron centres such that the spacing normal to paper feed between any nozzle and its neighbour in the offset row is the required 15.875 microns.

Fabricating the printhead chips (integrated circuits) using VLSI lithographic etching and deposition techniques is fundamental to the high nozzle densities that provide the 1600 dpi nozzle arrays that extend only 0.35 mm to 0.5 mm in the paper feed direction. As discussed below, prior art printheads have about 300 nozzles formed on a single monolithic substrate. The VLSI fabrication techniques and nozzle structures developed by the Applicant provide printheads with more than 2000 nozzles on a monolithic substrate with a high nozzle density. In the case of the IJ30 printhead shown in FIG. 23, the nozzle pitch along each row e.g. 192 and 193 is 32 microns. As FIG. 23 is to scale, it can be seen that the nozzle chambers are each 72 microns long and the ink supply channel 194 between each nozzle row is 48 microns wide. The eleven nozzles shown in rows 192 and 193 occupy 33,792 square microns of the wafer. Hence the overall nozzle density for the IJ30 is about 325 nozzles per square mm.

Currently, nozzle densities on scanning printhead chips are of the order of 10 to 20 nozzles per square mm. It will be appreciated that the combination of VLSI CMOS fabrication and subsequent MEMS fabrication allow nozzle densities to easily exceed 100 nozzles per square mm and comfortably exceed 200 nozzles per square mm using lithographic techniques employed in the semiconductor industry. Design elements such as ink supply conduits extending through the wafer to the nozzles (instead along the ejection side of the wafer) can further increase the nozzle densities above 300 nozzles per square mm. The Applicant's IJ38 chip design (discussed below) is the thinnest of the 100 mm long chips at just 0.35 mm wide and has a nozzle density of about 548 nozzles per square mm.

One form of detailed manufacturing process which can be used to fabricate monolithic inkjet printheads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

1. Using a double sided polished wafer 141, complete drive transistors, data distribution, and timing circuits using a 0.5 micron, one poly, two metal CMOS process 118. Relevant features of the wafer at this step are shown in FIG. 25. For clarity, these diagrams may not be to scale, and may not represent a cross section though any single plane of the nozzle. FIG. 24 is a key to representations of various materials in these manufacturing diagrams, and those of other cross referenced ink jet configurations.

2. Deposit 1 micron of low stress nitride 142. This acts as a barrier to prevent ink diffusion through the silicon dioxide of the chip surface.

3. Deposit 2 microns of sacrificial material 160 (e.g. polyimide).

4. Etch the sacrificial layer to define the PTFE venting layer support pillars e.g. 127 and anchor point. This step is shown in FIG. 26.

5. Deposit 2 microns of PTFE 126.

6. Etch the PTFE using Mask 2. This mask defines the edges of the PTFE venting layer, and the holes in this layer. This step is shown in FIG. 27.

7. Deposit 3 micron of sacrificial material 161 (e.g. polyimide).

8. Etch the sacrificial layer using Mask 3. This mask defines the actuator anchor point. This step is shown in FIG. 28.

9. Deposit 1 micron of PTFE.

10. Deposit, expose and develop 1 micron of resist using Mask 4. This mask is a gray-scale mask which defines the heater vias as well as the corrugated PTFE surface 162 that the heater is subsequently deposited on.

11. Etch the PTFE and resist at substantially the same rate. The corrugated resist thickness is transferred to the PTFE, and the PTFE is completely etched in the heater via positions. In the corrugated regions, the resultant PTFE thickness nominally varies between 0.25 micron and 0.75 micron, though exact values are not critical. This step is shown in FIG. 29.

12. Deposit and pattern resist using Mask 5. This mask defines the heater.

13. Deposit 0.5 microns of gold 163 (or other heater material with a low Young's modulus) and strip the resist. Steps 12 and 13 form a lift-off process. This step is shown in FIG. 30.

14. Deposit 1.5 microns of PTFE 116.

15. Etch the PTFE down to the sacrificial layer to define the actuator paddle and the bond pads.

This step is shown in FIG. 31.

16. Wafer probe. All electrical connections are complete at this point, and the chips are not yet separated.

17. Plasma process the PTFE to make the top and side surfaces of the paddle hydrophilic. This allows the nozzle chamber to fill by capillarity.

18. Deposit 10 microns of sacrificial material 164.

19. Etch the sacrificial material down to nitride to define the nozzle chamber. This step is shown in FIG. 32.

20. Deposit 3 microns of PECVD glass 146. This step is shown in FIG. 33.

21. Etch to a depth of 1 micron to define the nozzle rim 165. This step is shown in FIG. 34.

22. Etch down to the sacrificial layer to define the nozzle and the sacrificial etch access holes e.g. 119. This step is shown in FIG. 35.

23. Back-etch completely through the silicon wafer (with, for example, an ASE Advanced Silicon Etcher from Surface Technology Systems). This mask defines the ink inlets 138 which are etched through the wafer. The wafer is also diced by this etch. This step is shown in FIG. 36.

24. Back-etch the CMOS oxide layers and subsequently deposited nitride layers and sacrificial layer through to PTFE using the back-etched silicon as a mask.

25. Etch the sacrificial material. The nozzle chambers are cleared, the actuators freed, and the chips are separated by this etch. This step is shown in FIG. 37.

26. Mount the printheads in their packaging, which may be a molded plastic former incorporating ink channels which supply the appropriate color ink to the ink inlets at the back of the wafer.

27. Connect the printheads to their interconnect systems. For a low profile connection with minimum disruption of airflow, TAB may be used. Wire bonding may also be used if the printer is to be operated with sufficient clearance to the paper.

28. Hydrophobize the front surface of the printheads.

29. Fill the completed printheads with ink 166 and test them. A filled nozzle is shown in FIG. 38.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. Some possible variations are disclosed in the cross referenced documents listed above and incorporated herein. These disclosures provide an indication of the scope of possible and highlight that the embodiments described above are merely illustrative and in no way restrictive.

The presently disclosed ink jet printing technology is potentially suited to a wide range of printing systems including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers, high speed pagewidth printers, notebook computers with inbuilt pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic ‘minilabs’, video printers, PHOTO CD (PHOTO CD is a registered trademark of the Eastman Kodak Company) printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

Inkjet Technologies

The embodiments of the invention use an inkjet printer type device. Of course many different devices could be used. However presently popular inkjet printing technologies are unlikely to be suitable.

The most significant problem with vapor bubble forming thermal inkjet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per printhead, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts average consumption for 100% coverage printing from pagewidth printhead)

high resolution capability (1,600 dpi or more)

photographic quality output low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the inkjet systems described in the tables set out below with differing levels of difficulty. Forty-five different ink jet technologies (Assignee's Docket Numbers IJ01 to IJ45) have been developed by the Assignee to give a wide range of choices for high volume manufacture. The droplet ejector mechanisms in each of IJ01 to IJ45 offer substantial advantages over existing printheads, primarily by reducing the energy required to eject a droplet of ink. As discussed in the Actuator Mechanism Table below, the IJ30 actuator uses only 15 mW to move the free end of the actuator 113 (see FIG. 16) 10 microns with a force of 180 micro-Newtons. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.

The inkjet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.

For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry such that the monolithic silicon substrate supports and array of nozzles with a nozzle density of 548 nozzles per square mm. The printhead uses less than 10 Watts and so the average power consumption of each nozzle is less than 0.502 mW. It will be appreciated that this is a huge improvement over the power consumption of existing electro-thermally actuated printheads. For example, the device shown in U.S. Pat. No. 4,490,728 to Vaught et al uses about 0.3 W to 0.5 W per nozzle (given a nozzle fire rate of 10 Hz and a pulse width of 5 micro-seconds is not unreasonable for this type of printhead). Accordingly, even if the electro-thermal actuator of IJ30 were modified to eject larger droplets (say, 5 μl or 10 μl) or fabricated using material with a marginally lower CTE, the power consumption per nozzle during activation of the would be easily less than 1.5 mW, more likely less than 1.0 mW and typically in the range of 0.5 mW to 1.0 mW. It will be appreciated that these power consumption values are average values taken when the printhead is printing 100% coverage at full print rate.

The peak power consumption during activation of the IJ30 actuator is much higher than the time averaged power. However, it is still far lower than that of existing electro-thermal actuators. The Vaught et al printhead discussed above has a peak actuator power of 3 W. Using the principles of the IJ30 electro-thermal actuator, the peak power consumption is less than 100 mW even if 5 μl drops are ejected and actuator material has a CTE marginally less than PTFE. Using the IJ30 design principles and as the VLSI fabrication techniques described herein, an activation power of less than 50 mW is easily attainable. As discussed below in the Table of Actuator Types, the activation power for the IJ30 actuator is 15 mW. However, with variation of design parameters such as the droplet volume and nozzle to actuator spacing, the activation power will typically vary between 10 mW and 30 mW.

With low energy ejection of ink droplets, little, if any, excess heat is generated in the printhead. A build up of excess heat in the printhead imposes a limit on the nozzle firing frequency and thereby limits the print speed. The IJ30 printhead is self cooling (the heat generated by the thermal actuator is removed from the printhead with the ejected drop. In this case, the print speed is only limited by the rate at which the ink can be supplied to the printhead or the speed that the media substrate can be fed past the printhead. Printers using the IJ30 printhead will accommodate a media substrate feed speed relative to the printhead in excess of 0.1 m/s. Indeed, when used in a printer such as that shown in the Assignee's U.S. Pat. No. 7,011,128 (the contents of which are incorporated herein by reference), the media feed speed is greater than 0.15 m/s.

An A4 sheet printed at 1600 dpi has about 18,600 dots rows across the page. Accordingly, the IJ30 printhead in a pagewidth form prints at least 6300 rows/sec or less than 0.00016 secs per dot row. Typically, the row printing frequency is more than 9450 rows/sec or less than 0.000106 secs per dot row.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micro-machined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain inkjet types have been investigated in detail. These are designated IJ01 to IJ45 which match the docket numbers in the table under the heading Cross Referenced to Related Application.

Other inkjet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available inkjet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix is set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS)
DescriptionAdvantagesDisadvantagesExamples
ThermalAn electrothermalLarge forceHigh powerCanon Bubblejet
bubbleheater heats the ink togeneratedInk carrier1979 Endo et al GB
above boiling point,Simplelimited to waterpatent 2,007,162
transferring significantconstructionLow efficiencyXerox heater-in-
heat to the aqueousNo moving partsHighpit 1990 Hawkins et
ink. A bubbleFast operationtemperaturesal U.S. Pat. No. 4,899,181
nucleates and quicklySmall chip arearequiredHewlett-Packard
forms, expelling therequired for actuatorHigh mechanicalTIJ 1982 Vaught et
ink.stressal U.S. Pat. No. 4,490,728
The efficiency of theUnusual
process is low, withmaterials required
typically less thanLarge drive
0.05% of the electricaltransistors
energy beingCavitation causes
transformed intoactuator failure
kinetic energy of theKogation reduces
drop.bubble formation
Large print heads
are difficult to
fabricate
PiezoelectricA piezoelectric crystalLow powerVery large areaKyser et al U.S. Pat. No.
such as leadconsumptionrequired for actuator3,946,398
lanthanum zirconateMany ink typesDifficult toZoltan U.S. Pat. No.
(PZT) is electricallycan be usedintegrate with3,683,212
activated, and eitherFast operationelectronics1973 Stemme
expands, shears, orHigh efficiencyHigh voltageU.S. Pat. No. 3,747,120
bends to applydrive transistorsEpson Stylus
pressure to the ink,requiredTektronix
ejecting drops.Full pagewidthIJ04
print heads
impractical due to
actuator size
Requires
electrical poling in
high field strengths
during manufacture
Electro-An electric field isLow powerLow maximumSeiko Epson,
strictiveused to activateconsumptionstrain (approx.Usui et all JP
electrostriction inMany ink types0.01%)253401/96
relaxor materials suchcan be usedLarge areaIJ04
as lead lanthanumLow thermalrequired for actuator
zirconate titanateexpansiondue to low strain
(PLZT) or leadElectric fieldResponse speed
magnesium niobatestrength requiredis marginal (~ 10 μs)
(PMN).(approx. 3.5 V/μm)High voltage
can be generateddrive transistors
without difficultyrequired
Does not requireFull pagewidth
electrical polingprint heads
impractical due to
actuator size
FerroelectricAn electric field isLow powerDifficult toIJ04
used to induce a phaseconsumptionintegrate with
transition between theMany ink typeselectronics
antiferroelectric (AFE)can be usedUnusual
and ferroelectric (FE)Fast operationmaterials such as
phase. Perovskite(<1 μs)PLZSnT are
materials such as tinRelatively highrequired
modified leadlongitudinal strainActuators require
lanthanum zirconateHigh efficiencya large area
titanate (PLZSnT)Electric field
exhibit large strains ofstrength of around 3 V/μm
up to 1% associatedcan be readily
with the AFE to FEprovided
phase transition.
ElectrostaticConductive plates areLow powerDifficult toIJ02, IJ04
platesseparated by aconsumptionoperate electrostatic
compressible or fluidMany ink typesdevices in an
dielectric (usually air).can be usedaqueous
Upon application of aFast operationenvironment
voltage, the platesThe electrostatic
attract each other andactuator will
displace ink, causingnormally need to be
drop ejection. Theseparated from the
conductive plates mayink
be in a comb orVery large area
honeycomb structure,required to achieve
or stacked to increasehigh forces
the surface area andHigh voltage
therefore the force.drive transistors
may be required
Full pagewidth
print heads are not
competitive due to
actuator size
ElectrostaticA strong electric fieldLow currentHigh voltage1989 Saito et al,
pullis applied to the ink,consumptionrequiredU.S. Pat. No. 4,799,068
on inkwhereuponLow temperatureMay be damaged1989 Miura et al,
electrostatic attractionby sparks due to airU.S. Pat. No. 4,810,954
accelerates the inkbreakdownTone-jet
towards the printRequired field
medium.strength increases as
the drop size
decreases
High voltage
drive transistors
required
Electrostatic field
attracts dust
PermanentAn electromagnetLow powerComplexIJ07, IJ10
magnetdirectly attracts aconsumptionfabrication
electro-permanent magnet,Many ink typesPermanent
magneticdisplacing ink andcan be usedmagnetic material
causing drop ejection.Fast operationsuch as Neodymium
Rare earth magnetsHigh efficiencyIron Boron (NdFeB)
with a field strengthEasy extensionrequired.
around 1 Tesla can befrom single nozzlesHigh local
used. Examples are:to pagewidth printcurrents required
Samarium CobaltheadsCopper
(SaCo) and magneticmetalization should
materials in thebe used for long
neodymium iron boronelectromigration
family (NdFeB,lifetime and low
NdDyFeBNb,resistivity
NdDyFeB, etc)Pigmented inks
are usually
infeasible
Operating
temperature limited
to the Curie
temperature (around
540 K)
SoftA solenoid induced aLow powerComplexIJ01, IJ05, IJ08,
magneticmagnetic field in a softconsumptionfabricationIJ10, IJ12, IJ14,
core electro-magnetic core or yokeMany ink typesMaterials notIJ15, IJ17
magneticfabricated from acan be usedusually present in a
ferrous material suchFast operationCMOS fab such as
as electroplated ironHigh efficiencyNiFe, CoNiFe, or
alloys such as CoNiFeEasy extensionCoFe are required
[1], CoFe, or NiFefrom single nozzlesHigh local
alloys. Typically, theto pagewidth printcurrents required
soft magnetic materialheadsCopper
is in two parts, whichmetalization should
are normally heldbe used for long
apart by a spring.electromigration
When the solenoid islifetime and low
actuated, the two partsresistivity
attract, displacing theElectroplating is
ink.required
High saturation
flux density is
required (2.0-2.1 T
is achievable with
CoNiFe [1])
LorenzThe Lorenz forceLow powerForce acts as aIJ06, IJ11, IJ13,
forceacting on a currentconsumptiontwisting motionIJ16
carrying wire in aMany ink typesTypically, only a
magnetic field iscan be usedquarter of the
utilized.Fast operationsolenoid length
This allows theHigh efficiencyprovides force in a
magnetic field to beEasy extensionuseful direction
supplied externally tofrom single nozzlesHigh local
the print head, forto pagewidth printcurrents required
example with rareheadsCopper
earth permanentmetalization should
magnets.be used for long
Only the currentelectromigration
carrying wire need belifetime and low
fabricated on the print-resistivity
head, simplifyingPigmented inks
materialsare usually
requirements.infeasible
Magneto-The actuator uses theMany ink typesForce acts as aFischenbeck,
strictiongiant magnetostrictivecan be usedtwisting motionU.S. Pat. No. 4,032,929
effect of materialsFast operationUnusualIJ25
such as Terfenol-D (anEasy extensionmaterials such as
alloy of terbium,from single nozzlesTerfenol-D are
dysprosium and ironto pagewidth printrequired
developed at the NavalheadsHigh local
Ordnance Laboratory,High force iscurrents required
hence Ter-Fe-NOL).availableCopper
For best efficiency, themetalization should
actuator should be pre-be used for long
stressed to approx. 8 MPa.electromigration
lifetime and low
resistivity
Pre-stressing
may be required
SurfaceInk under positiveLow powerRequiresSilverbrook, EP
tensionpressure is held in aconsumptionsupplementary force0771 658 A2 and
reductionnozzle by surfaceSimpleto effect droprelated patent
tension. The surfaceconstructionseparationapplications
tension of the ink isNo unusualRequires special
reduced below thematerials required inink surfactants
bubble threshold,fabricationSpeed may be
causing the ink toHigh efficiencylimited by surfactant
egress from theEasy extensionproperties
nozzle.from single nozzles
to pagewidth print
heads
ViscosityThe ink viscosity isSimpleRequiresSilverbrook, EP
reductionlocally reduced toconstructionsupplementary force0771 658 A2 and
select which drops areNo unusualto effect droprelated patent
to be ejected. Amaterials required inseparationapplications
viscosity reduction canfabricationRequires special
be achievedEasy extensionink viscosity
electrothermally withfrom single nozzlesproperties
most inks, but specialto pagewidth printHigh speed is
inks can be engineeredheadsdifficult to achieve
for a 100:1 viscosityRequires
reduction.oscillating ink
pressure
A high
temperature
difference (typically
80 degrees) is
required
AcousticAn acoustic wave isCan operateComplex drive1993 Hadimioglu
generated andwithout a nozzlecircuitryet al, EUP 550,192
focussed upon theplateComplex1993 Elrod et al,
drop ejection region.fabricationEUP 572,220
Low efficiency
Poor control of
drop position
Poor control of
drop volume
Thermo-An actuator whichLow powerEfficient aqueousIJ03, IJ09, IJ17,
elastic bendrelies upon differentialconsumptionoperation requires aIJ18, IJ19, IJ20,
actuatorthermal expansionMany ink typesthermal insulator onIJ21, IJ22, IJ23,
upon Joule heating iscan be usedthe hot sideIJ24, IJ27, IJ28,
used.Simple planarCorrosionIJ29, IJ30, IJ31,
fabricationprevention can beIJ32, IJ33, IJ34,
Small chip areadifficultIJ35, IJ36, IJ37,
required for eachPigmented inksIJ38, IJ39, IJ40,
actuatormay be infeasible,IJ41
Fast operationas pigment particles
High efficiencymay jam the bend
CMOSactuator
compatible voltages
and currents
Standard MEMS
processes can be
used
Easy extension
from single nozzles
to pagewidth print
heads
High CTEA material with a veryHigh force canRequires specialIJ09, IJ17, IJ18,
thermo-high coefficient ofbe generatedmaterial (e.g. PTFE)IJ20, IJ21, IJ22,
elasticthermal expansionThree methods ofRequires a PTFEIJ23, IJ24, IJ27,
actuator(CTE) such asPTFE deposition aredeposition process,IJ28, IJ29, IJ30,
polytetrafluoroethyleneunder development:which is not yetIJ31, IJ42, IJ43,
(PTFE) is used. Aschemical vaporstandard in ULSIIJ44
high CTE materialsdeposition (CVD),fabs
are usually non-spin coating, andPTFE deposition
conductive, a heaterevaporationcannot be followed
fabricated from aPTFE is awith high
conductive material iscandidate for lowtemperature (above
incorporated. A 50 μmdielectric constant350° C.) processing
long PTFE bendinsulation in ULSIPigmented inks
actuator withVery low powermay be infeasible,
polysilicon heater andconsumptionas pigment particles
15 mW power inputMany ink typesmay jam the bend
can provide 180 μNcan be usedactuator
force and 10 μmSimple planar
deflection. Actuatorfabrication
motions include:Small chip area
Bendrequired for each
Pushactuator
BuckleFast operation
RotateHigh efficiency
CMOS
compatible voltages
and currents
Easy extension
from single nozzles
to pagewidth print
heads
ConductiveA polymer with a highHigh force canRequires specialIJ24
polymercoefficient of thermalbe generatedmaterials
thermo-expansion (such asVery low powerdevelopment (High
elasticPTFE) is doped withconsumptionCTE conductive
actuatorconducting substancesMany ink typespolymer)
to increase itscan be usedRequires a PTFE
conductivity to about 3Simple planardeposition process,
orders of magnitudefabricationwhich is not yet
below that of copper.Small chip areastandard in ULSI
The conductingrequired for eachfabs
polymer expandsactuatorPTFE deposition
when resistivelyFast operationcannot be followed
heated.High efficiencywith high
Examples ofCMOStemperature (above
conducting dopantscompatible voltages350° C.) processing
include:and currentsEvaporation and
Carbon nanotubesEasy extensionCVD deposition
Metal fibersfrom single nozzlestechniques cannot
Conductive polymersto pagewidth printbe used
such as dopedheadsPigmented inks
polythiophenemay be infeasible,
Carbon granulesas pigment particles
may jam the bend
actuator
ShapeA shape memory alloyHigh force isFatigue limitsIJ26
memorysuch as TiNi (alsoavailable (stressesmaximum number
alloyknown as Nitinol -of hundreds of MPa)of cycles
Nickel Titanium alloyLarge strain isLow strain (1%)
developed at the Navalavailable (more thanis required to extend
Ordnance Laboratory)3%)fatigue resistance
is thermally switchedHigh corrosionCycle rate
between its weakresistancelimited by heat
martensitic state andSimpleremoval
its high stiffnessconstructionRequires unusual
austenic state. TheEasy extensionmaterials (TiNi)
shape of the actuatorfrom single nozzlesThe latent heat of
in its martensitic stateto pagewidth printtransformation must
is deformed relative toheadsbe provided
the austenic shape.Low voltageHigh current
The shape changeoperationoperation
causes ejection of aRequires pre-
drop.stressing to distort
the martensitic state
LinearLinear magneticLinear MagneticRequires unusualIJ12
Magneticactuators include theactuators can besemiconductor
ActuatorLinear Inductionconstructed withmaterials such as
Actuator (LIA), Linearhigh thrust, longsoft magnetic alloys
Permanent Magnettravel, and high(e.g. CoNiFe)
Synchronous Actuatorefficiency usingSome varieties
(LPMSA), Linearplanaralso require
Reluctancesemiconductorpermanent magnetic
Synchronous Actuatorfabricationmaterials such as
(LRSA), LineartechniquesNeodymium iron
Switched ReluctanceLong actuatorboron (NdFeB)
Actuator (LSRA), andtravel is availableRequires
the Linear StepperMedium force iscomplex multi-
Actuator (LSA).availablephase drive circuitry
Low voltageHigh current
operationoperation

BASIC OPERATION MODE
DescriptionAdvantagesDisadvantagesExamples
ActuatorThis is the simplestSimple operationDrop repetitionThermal ink jet
directlymode of operation: theNo externalrate is usuallyPiezoelectric ink
pushes inkactuator directlyfields requiredlimited to around 10 kHz.jet
supplies sufficientSatellite dropsHowever, thisIJ01, IJ02, IJ03,
kinetic energy to expelcan be avoided ifis not fundamentalIJ04, IJ05, IJ06,
the drop. The dropdrop velocity is lessto the method, but isIJ07, IJ09, IJ11,
must have a sufficientthan 4 m/srelated to the refillIJ12, IJ14, IJ16,
velocity to overcomeCan be efficient,method normallyIJ20, IJ22, IJ23,
the surface tension.depending upon theusedIJ24, IJ25, IJ26,
actuator usedAll of the dropIJ27, IJ28, IJ29,
kinetic energy mustIJ30, IJ31, IJ32,
be provided by theIJ33, IJ34, IJ35,
actuatorIJ36, IJ37, IJ38,
Satellite dropsIJ39, IJ40, IJ41,
usually form if dropIJ42, IJ43, IJ44
velocity is greater
than 4.5 m/s
ProximityThe drops to beVery simple printRequires closeSilverbrook, EP
printed are selected byhead fabrication canproximity between0771 658 A2 and
some manner (e.g.be usedthe print head andrelated patent
thermally inducedThe dropthe print media orapplications
surface tensionselection meanstransfer roller
reduction ofdoes not need toMay require two
pressurized ink).provide the energyprint heads printing
Selected drops arerequired to separatealternate rows of the
separated from the inkthe drop from theimage
in the nozzle bynozzleMonolithic color
contact with the printprint heads are
medium or a transferdifficult
roller.
ElectrostaticThe drops to beVery simple printRequires verySilverbrook, EP
pullprinted are selected byhead fabrication canhigh electrostatic0771 658 A2 and
on inksome manner (e.g.be usedfieldrelated patent
thermally inducedThe dropElectrostatic fieldapplications
surface tensionselection meansfor small nozzleTone-Jet
reduction ofdoes not need tosizes is above air
pressurized ink).provide the energybreakdown
Selected drops arerequired to separateElectrostatic field
separated from the inkthe drop from themay attract dust
in the nozzle by anozzle
strong electric field.
MagneticThe drops to beVery simple printRequiresSilverbrook, EP
pull on inkprinted are selected byhead fabrication canmagnetic ink0771 658 A2 and
some manner (e.g.be usedInk colors otherrelated patent
thermally inducedThe dropthan black areapplications
surface tensionselection meansdifficult
reduction ofdoes not need toRequires very
pressurized ink).provide the energyhigh magnetic fields
Selected drops arerequired to separate
separated from the inkthe drop from the
in the nozzle by anozzle
strong magnetic field
acting on the magnetic
ink.
ShutterThe actuator moves aHigh speed (>50 kHz)Moving parts areIJ13, IJ17, IJ21
shutter to block inkoperation canrequired
flow to the nozzle. Thebe achieved due toRequires ink
ink pressure is pulsedreduced refill timepressure modulator
at a multiple of theDrop timing canFriction and wear
drop ejectionbe very accuratemust be considered
frequency.The actuatorStiction is
energy can be verypossible
low
ShutteredThe actuator moves aActuators withMoving parts areIJ08, IJ15, IJ18,
grillshutter to block inksmall travel can berequiredIJ19
flow through a grill tousedRequires ink
the nozzle. The shutterActuators withpressure modulator
movement need onlysmall force can beFriction and wear
be equal to the widthusedmust be considered
of the grill holes.High speed (>50 kHz)Stiction is
operation canpossible
be achieved
PulsedA pulsed magneticExtremely lowRequires anIJ10
magneticfield attracts an ‘inkenergy operation isexternal pulsed
pull on inkpusher’ at the droppossiblemagnetic field
pusherejection frequency. AnNo heatRequires special
actuator controls adissipationmaterials for both
catch, which preventsproblemsthe actuator and the
the ink pusher fromink pusher
moving when a drop isComplex
not to be ejected.construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES)
DescriptionAdvantagesDisadvantagesExamples
NoneThe actuator directlySimplicity ofDrop ejectionMost ink jets,
fires the ink drop, andconstructionenergy must beincluding
there is no externalSimplicity ofsupplied bypiezoelectric and
field or otheroperationindividual nozzlethermal bubble.
mechanism required.Small physicalactuatorIJ01, IJ02, IJ03,
sizeIJ04, IJ05, IJ07,
IJ09, IJ11, IJ12,
IJ14, IJ20, IJ22,
IJ23, IJ24, IJ25,
IJ26, IJ27, IJ28,
IJ29, IJ30, IJ31,
IJ32, IJ33, IJ34,
IJ35, IJ36, IJ37,
IJ38, IJ39, IJ40,
IJ41, IJ42, IJ43,
IJ44
OscillatingThe ink pressureOscillating inkRequires externalSilverbrook, EP
ink pressureoscillates, providingpressure can provideink pressure0771 658 A2 and
(includingmuch of the dropa refill pulse,oscillatorrelated patent
acousticejection energy. Theallowing higherInk pressureapplications
stimulation)actuator selects whichoperating speedphase and amplitudeIJ08, IJ13, IJ15,
drops are to be firedThe actuatorsmust be carefullyIJ17, IJ18, IJ19,
by selectivelymay operate withcontrolledIJ21
blocking or enablingmuch lower energyAcoustic
nozzles. The inkAcoustic lensesreflections in the ink
pressure oscillationcan be used to focuschamber must be
may be achieved bythe sound on thedesigned for
vibrating the printnozzles
head, or preferably by
an actuator in the ink
supply.
MediaThe print head isLow powerPrecisionSilverbrook, EP
proximityplaced in closeHigh accuracyassembly required0771 658 A2 and
proximity to the printSimple print headPaper fibers mayrelated patent
medium. Selectedconstructioncause problemsapplications
drops protrude fromCannot print on
the print head furtherrough substrates
than unselected drops,
and contact the print
medium. The drop
soaks into the medium
fast enough to cause
drop separation.
TransferDrops are printed to aHigh accuracyBulkySilverbrook, EP
rollertransfer roller insteadWide range ofExpensive0771 658 A2 and
of straight to the printprint substrates canComplexrelated patent
medium. A transferbe usedconstructionapplications
roller can also be usedInk can be driedTektronix hot
for proximity dropon the transfer rollermelt piezoelectric
separation.ink jet
Any of the IJ
series
ElectrostaticAn electric field isLow powerField strengthSilverbrook, EP
used to accelerateSimple print headrequired for0771 658 A2 and
selected drops towardsconstructionseparation of smallrelated patent
the print medium.drops is near orapplications
above airTone-Jet
breakdown
DirectA magnetic field isLow powerRequiresSilverbrook, EP
magneticused to accelerateSimple print headmagnetic ink0771 658 A2 and
fieldselected drops ofconstructionRequires strongrelated patent
magnetic ink towardsmagnetic fieldapplications
the print medium.
CrossThe print head isDoes not requireRequires externalIJ06, IJ16
magneticplaced in a constantmagnetic materialsmagnet
fieldmagnetic field. Theto be integrated inCurrent densities
Lorenz force in athe print headmay be high,
current carrying wiremanufacturingresulting in
is used to move theprocesselectromigration
actuator.problems
PulsedA pulsed magneticVery low powerComplex printIJ10
magneticfield is used tooperation is possiblehead construction
fieldcyclically attract aSmall print headMagnetic
paddle, which pushessizematerials required in
on the ink. A smallprint head
actuator moves a
catch, which
selectively prevents
the paddle from
moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD
DescriptionAdvantagesDisadvantagesExamples
NoneNo actuatorOperationalMany actuatorThermal Bubble
mechanicalsimplicitymechanisms haveInk jet
amplification is used.insufficient travel,IJ01, IJ02, IJ06,
The actuator directlyor insufficient force,IJ07, IJ16, IJ25,
drives the dropto efficiently driveIJ26
ejection process.the drop ejection
process
DifferentialAn actuator materialProvides greaterHigh stresses arePiezoelectric
expansionexpands more on onetravel in a reducedinvolvedIJ03, IJ09, IJ17,
bendside than on the other.print head areaCare must beIJ18, IJ19, IJ20,
actuatorThe expansion may betaken that theIJ21, IJ22, IJ23,
thermal, piezoelectric,materials do notIJ24, IJ27, IJ29,
magnetostrictive, ordelaminateIJ30, IJ31, IJ32,
other mechanism. TheResidual bendIJ33, IJ34, IJ35,
bend actuator convertsresulting from highIJ36, IJ37, IJ38,
a high force low traveltemperature or highIJ39, IJ42, IJ43,
actuator mechanism tostress duringIJ44
high travel, lowerformation
force mechanism.
TransientA trilayer bendVery goodHigh stresses areIJ40, IJ41
bendactuator where the twotemperature stabilityinvolved
actuatoroutside layers areHigh speed, as aCare must be
identical. This cancelsnew drop can betaken that the
bend due to ambientfired before heatmaterials do not
temperature anddissipatesdelaminate
residual stress. TheCancels residual
actuator only respondsstress of formation
to transient heating of
one side or the other.
ReverseThe actuator loads aBetter couplingFabricationIJ05, IJ11
springspring. When theto the inkcomplexity
actuator is turned off,High stress in the
the spring releases.spring
This can reverse the
force/distance curve of
the actuator to make it
compatible with the
force/time
requirements of the
drop ejection.
ActuatorA series of thinIncreased travelIncreasedSome
stackactuators are stacked.Reduced drivefabricationpiezoelectric ink jets
This can bevoltagecomplexityIJ04
appropriate whereIncreased
actuators require highpossibility of short
electric field strength,circuits due to
such as electrostaticpinholes
and piezoelectric
actuators.
MultipleMultiple smallerIncreases theActuator forcesIJ12, IJ13, IJ18,
actuatorsactuators are usedforce available frommay not addIJ20, IJ22, IJ28,
simultaneously toan actuatorlinearly, reducingIJ42, IJ43
move the ink. EachMultipleefficiency
actuator need provideactuators can be
only a portion of thepositioned to control
force required.ink flow accurately
LinearA linear spring is usedMatches lowRequires printIJ15
Springto transform a motiontravel actuator withhead area for the
with small travel andhigher travelspring
high force into arequirements
longer travel, lowerNon-contact
force motion.method of motion
transformation
CoiledA bend actuator isIncreases travelGenerallyIJ17, IJ21, IJ34,
actuatorcoiled to provideReduces chiprestricted to planarIJ35
greater travel in aareaimplementations
reduced chip area.Planardue to extreme
implementations arefabrication difficulty
relatively easy toin other orientations.
fabricate.
FlexureA bend actuator has aSimple means ofCare must beIJ10, IJ19, IJ33
bendsmall region near theincreasing travel oftaken not to exceed
actuatorfixture point, whicha bend actuatorthe elastic limit in
flexes much morethe flexure area
readily than theStress
remainder of thedistribution is very
actuator. The actuatoruneven
flexing is effectivelyDifficult to
converted from anaccurately model
even coiling to anwith finite element
angular bend, resultinganalysis
in greater travel of the
actuator tip.
CatchThe actuator controls aVery lowComplexIJ10
small catch. The catchactuator energyconstruction
either enables orVery smallRequires external
disables movement ofactuator sizeforce
an ink pusher that isUnsuitable for
controlled in a bulkpigmented inks
manner.
GearsGears can be used toLow force, lowMoving parts areIJ13
increase travel at thetravel actuators canrequired
expense of duration.be usedSeveral actuator
Circular gears, rackCan be fabricatedcycles are required
and pinion, ratchets,using standardMore complex
and other gearingsurface MEMSdrive electronics
methods can be used.processesComplex
construction
Friction, friction,
and wear are
possible
Buckle plateA buckle plate can beVery fastMust stay withinS. Hirata et al,
used to change a slowmovementelastic limits of the“An Ink-jet Head
actuator into a fastachievablematerials for longUsing Diaphragm
motion. It can alsodevice lifeMicroactuator”,
convert a high force,High stressesProc. IEEE MEMS,
low travel actuatorinvolvedFebruary 1996, pp 418-423.
into a high travel,Generally highIJ18, IJ27
medium force motion.power requirement
TaperedA tapered magneticLinearizes theComplexIJ14
magneticpole can increasemagneticconstruction
poletravel at the expenseforce/distance curve
of force.
LeverA lever and fulcrum isMatches lowHigh stressIJ32, IJ36, IJ37
used to transform atravel actuator witharound the fulcrum
motion with smallhigher travel
travel and high forcerequirements
into a motion withFulcrum area has
longer travel andno linear movement,
lower force. The leverand can be used for
can also reverse thea fluid seal
direction of travel.
RotaryThe actuator isHigh mechanicalComplexIJ28
impellerconnected to a rotaryadvantageconstruction
impeller. A smallThe ratio of forceUnsuitable for
angular deflection ofto travel of thepigmented inks
the actuator results inactuator can be
a rotation of thematched to the
impeller vanes, whichnozzle requirements
push the ink againstby varying the
stationary vanes andnumber of impeller
out of the nozzle.vanes
AcousticA refractive orNo moving partsLarge area1993 Hadimioglu
lensdiffractive (e.g. zonerequiredet al, EUP 550,192
plate) acoustic lens isOnly relevant for1993 Elrod et al,
used to concentrateacoustic ink jetsEUP 572,220
sound waves.
SharpA sharp point is usedSimpleDifficult toTone-jet
conductiveto concentrate anconstructionfabricate using
pointelectrostatic field.standard VLSI
processes for a
surface ejecting ink-
jet
Only relevant for
electrostatic ink jets

ACTUATOR MOTION
DescriptionAdvantagesDisadvantagesExamples
VolumeThe volume of theSimpleHigh energy isHewlett-Packard
expansionactuator changes,construction in thetypically required toThermal Ink jet
pushing the ink in allcase of thermal inkachieve volumeCanon Bubblejet
directions.jetexpansion. This
leads to thermal
stress, cavitation,
and kogation in
thermal ink jet
implementations
Linear,The actuator moves inEfficientHigh fabricationIJ01, IJ02, IJ04,
normal toa direction normal tocoupling to inkcomplexity may beIJ07, IJ11, IJ14
chip surfacethe print head surface.drops ejectedrequired to achieve
The nozzle is typicallynormal to theperpendicular
in the line ofsurfacemotion
movement.
Parallel toThe actuator movesSuitable forFabricationIJ12, IJ13, IJ15,
chip surfaceparallel to the printplanar fabricationcomplexityIJ33,, IJ34, IJ35,
head surface. DropFrictionIJ36
ejection may still beStiction
normal to the surface.
MembraneAn actuator with aThe effectiveFabrication1982 Howkins
pushhigh force but smallarea of the actuatorcomplexityU.S. Pat. No. 4,459,601
area is used to push abecomes theActuator size
stiff membrane that ismembrane areaDifficulty of
in contact with the ink.integration in a
VLSI process
RotaryThe actuator causesRotary leversDeviceIJ05, IJ08, IJ13,
the rotation of somemay be used tocomplexityIJ28
element, such a grill orincrease travelMay have
impellerSmall chip areafriction at a pivot
requirementspoint
BendThe actuator bendsA very smallRequires the1970 Kyser et al
when energized. Thischange inactuator to be madeU.S. Pat. No. 3,946,398
may be due todimensions can befrom at least two1973 Stemme
differential thermalconverted to a largedistinct layers, or toU.S. Pat. No. 3,747,120
expansion,motion.have a thermalIJ03, IJ09, IJ10,
piezoelectricdifference across theIJ19, IJ23, IJ24,
expansion,actuatorIJ25, IJ29, IJ30,
magnetostriction, orIJ31, IJ33, IJ34,
other form of relativeIJ35
dimensional change.
SwivelThe actuator swivelsAllows operationInefficientIJ06
around a central pivot.where the net linearcoupling to the ink
This motion is suitableforce on the paddlemotion
where there areis zero
opposite forcesSmall chip area
applied to oppositerequirements
sides of the paddle,
e.g. Lorenz force.
StraightenThe actuator isCan be used withRequires carefulIJ26, IJ32
normally bent, andshape memorybalance of stresses
straightens whenalloys where theto ensure that the
energized.austenic phase isquiescent bend is
planaraccurate
DoubleThe actuator bends inOne actuator canDifficult to makeIJ36, IJ37, IJ38
bendone direction whenbe used to powerthe drops ejected by
one element istwo nozzles.both bend directions
energized, and bendsReduced chipidentical.
the other way whensize.A small
another element isNot sensitive toefficiency loss
energized.ambient temperaturecompared to
equivalent single
bend actuators.
ShearEnergizing theCan increase theNot readily1985 Fishbeck
actuator causes a sheareffective travel ofapplicable to otherU.S. Pat. No. 4,584,590
motion in the actuatorpiezoelectricactuator
material.actuatorsmechanisms
Radial constrictionThe actuator squeezesRelatively easyHigh force1970 Zoltan U.S. Pat. No.
an ink reservoir,to fabricate singlerequired3,683,212
forcing ink from anozzles from glassInefficient
constricted nozzle.tubing asDifficult to
macroscopicintegrate with VLSI
structuresprocesses
Coil/uncoilA coiled actuatorEasy to fabricateDifficult toIJ17, IJ21, IJ34,
uncoils or coils moreas a planar VLSIfabricate for non-IJ35
tightly. The motion ofprocessplanar devices
the free end of theSmall areaPoor out-of-plane
actuator ejects the ink.required, thereforestiffness
low cost
BowThe actuator bows (orCan increase theMaximum travelIJ16, IJ18, IJ27
buckles) in the middlespeed of travelis constrained
when energized.MechanicallyHigh force
rigidrequired
Push-PullTwo actuators controlThe structure isNot readilyIJ18
a shutter. One actuatorpinned at both ends,suitable for ink jets
pulls the shutter, andso has a high out-of-which directly push
the other pushes it.plane rigiditythe ink
CurlA set of actuators curlGood fluid flowDesignIJ20, IJ42
inwardsinwards to reduce theto the region behindcomplexity
volume of ink thatthe actuator
they enclose.increases efficiency
CurlA set of actuators curlRelatively simpleRelatively largeIJ43
outwardsoutwards, pressurizingconstructionchip area
ink in a chamber
surrounding the
actuators, and
expelling ink from a
nozzle in the chamber.
IrisMultiple vanes encloseHigh efficiencyHigh fabricationIJ22
a volume of ink. TheseSmall chip areacomplexity
simultaneously rotate,Not suitable for
reducing the volumepigmented inks
between the vanes.
AcousticThe actuator vibratesThe actuator canLarge area1993 Hadimioglu
vibrationat a high frequency.be physically distantrequired foret al, EUP 550,192
from the inkefficient operation1993 Elrod et al,
at useful frequenciesEUP 572,220
Acoustic
coupling and
crosstalk
Complex drive
circuitry
Poor control of
drop volume and
position
NoneIn various ink jetNo moving partsVarious otherSilverbrook, EP
designs the actuatortradeoffs are0771 658 A2 and
does not move.required torelated patent
eliminate movingapplications
partsTone-jet

NOZZLE REFILL METHOD
DescriptionAdvantagesDisadvantagesExamples
SurfaceThis is the normal wayFabricationLow speedThermal ink jet
tensionthat ink jets aresimplicitySurface tensionPiezoelectric ink
refilled. After theOperationalforce relativelyjet
actuator is energized,simplicitysmall compared toIJ01-IJ07, IJ10-IJ14,
it typically returnsactuator forceIJ16, IJ20,
rapidly to its normalLong refill timeIJ22-IJ45
position. This rapidusually dominates
return sucks in airthe total repetition
through the nozzlerate
opening. The ink
surface tension at the
nozzle then exerts a
small force restoring
the meniscus to a
minimum area. This
force refills the nozzle.
ShutteredInk to the nozzleHigh speedRequiresIJ08, IJ13, IJ15,
oscillatingchamber is provided atLow actuatorcommon inkIJ17, IJ18, IJ19,
ink pressurea pressure thatenergy, as thepressure oscillatorIJ21
oscillates at twice theactuator need onlyMay not be
drop ejectionopen or close thesuitable for
frequency. When ashutter, instead ofpigmented inks
drop is to be ejected,ejecting the ink drop
the shutter is opened
for 3 half cycles: drop
ejection, actuator
return, and refill. The
shutter is then closed
to prevent the nozzle
chamber emptying
during the next
negative pressure
cycle.
RefillAfter the mainHigh speed, asRequires twoIJ09
actuatoractuator has ejected athe nozzle isindependent
drop a second (refill)actively refilledactuators per nozzle
actuator is energized.
The refill actuator
pushes ink into the
nozzle chamber. The
refill actuator returns
slowly, to prevent its
return from emptying
the chamber again.
Positive inkThe ink is held a slightHigh refill rate,Surface spillSilverbrook, EP
pressurepositive pressure.therefore a highmust be prevented0771 658 A2 and
After the ink drop isdrop repetition rateHighlyrelated patent
ejected, the nozzleis possiblehydrophobic printapplications
chamber fills quicklyhead surfaces areAlternative for:,
as surface tension andrequiredIJ01-IJ07, IJ10-IJ14,
ink pressure bothIJ16, IJ20, IJ22-IJ45
operate to refill the
nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET
DescriptionAdvantagesDisadvantagesExamples
Long inletThe ink inlet channelDesign simplicityRestricts refillThermal ink jet
channelto the nozzle chamberOperationalratePiezoelectric ink
is made long andsimplicityMay result in ajet
relatively narrow,Reducesrelatively large chipIJ42, IJ43
relying on viscouscrosstalkarea
drag to reduce inletOnly partially
back-flow.effective
Positive inkThe ink is under aDrop selectionRequires aSilverbrook, EP
pressurepositive pressure, soand separationmethod (such as a0771 658 A2 and
that in the quiescentforces can benozzle rim orrelated patent
state some of the inkreducedeffectiveapplications
drop already protrudesFast refill timehydrophobizing, orPossible
from the nozzle.both) to preventoperation of the
This reduces theflooding of thefollowing: IJ01-IJ07,
pressure in the nozzleejection surface ofIJ09-IJ12,
chamber which isthe print head.IJ14, IJ16, IJ20,
required to eject aIJ22,, IJ23-IJ34,
certain volume of ink.IJ36-IJ41, IJ44
The reduction in
chamber pressure
results in a reduction
in ink pushed out
through the inlet.
BaffleOne or more bafflesThe refill rate isDesignHP Thermal Ink
are placed in the inletnot as restricted ascomplexityJet
ink flow. When thethe long inletMay increaseTektronix
actuator is energized,method.fabricationpiezoelectric ink jet
the rapid inkReducescomplexity (e.g.
movement createscrosstalkTektronix hot melt
eddies which restrictPiezoelectric print
the flow through theheads).
inlet. The slower refill
process is unrestricted,
and does not result in
eddies.
Flexible flapIn this method recentlySignificantlyNot applicable toCanon
restrictsdisclosed by Canon,reduces back-flowmost ink jet
inletthe expanding actuatorfor edge-shooterconfigurations
(bubble) pushes on athermal ink jetIncreased
flexible flap thatdevicesfabrication
restricts the inlet.complexity
Inelastic
deformation of
polymer flap results
in creep over
extended use
Inlet filterA filter is locatedAdditionalRestricts refillIJ04, IJ12, IJ24,
between the ink inletadvantage of inkrateIJ27, IJ29, IJ30
and the nozzlefiltrationMay result in
chamber. The filterInk filter may becomplex
has a multitude offabricated with noconstruction
small holes or slots,additional process
restricting ink flow.steps
The filter also removes
particles which may
block the nozzle.
Small inletThe ink inlet channelDesign simplicityRestricts refillIJ02, IJ37, IJ44
comparedto the nozzle chamberrate
to nozzlehas a substantiallyMay result in a
smaller cross sectionrelatively large chip
than that of the nozzle,area
resulting in easier inkOnly partially
egress out of theeffective
nozzle than out of the
inlet.
Inlet shutterA secondary actuatorIncreases speedRequires separateIJ09
controls the position ofof the ink-jet printrefill actuator and
a shutter, closing offhead operationdrive circuit
the ink inlet when the
main actuator is
energized.
The inlet isThe method avoids theBack-flowRequires carefulIJ01, IJ03, IJ05,
locatedproblem of inlet back-problem isdesign to minimizeIJ06, IJ07, IJ10,
behind theflow by arranging theeliminatedthe negativeIJ11, IJ14, IJ16,
ink-pushingink-pushing surface ofpressure behind theIJ22, IJ23, IJ25,
surfacethe actuator betweenpaddleIJ28, IJ31, IJ32,
the inlet and theIJ33, IJ34, IJ35,
nozzle.IJ36, IJ39, IJ40,
IJ41
Part of theThe actuator and aSignificantSmall increase inIJ07, IJ20, IJ26,
actuatorwall of the inkreductions in back-fabricationIJ38
moves tochamber are arrangedflow can becomplexity
shut off theso that the motion ofachieved
inletthe actuator closes offCompact designs
the inlet.possible
NozzleIn some configurationsInk back-flowNone related toSilverbrook, EP
actuatorof ink jet, there is noproblem isink back-flow on0771 658 A2 and
does notexpansion oreliminatedactuationrelated patent
result in inkmovement of anapplications
back-flowactuator which mayValve-jet
cause ink back-flowTone-jet
through the inlet.

NOZZLE CLEARING METHOD
DescriptionAdvantagesDisadvantagesExamples
NormalAll of the nozzles areNo addedMay not beMost ink jet
nozzle firingfired periodically,complexity on thesufficient tosystems
before the ink has aprint headdisplace dried inkIJ01, IJ02, IJ03,
chance to dry. WhenIJ04, IJ05, IJ06,
not in use the nozzlesIJ07, IJ09, IJ10,
are sealed (capped)IJ11, IJ12, IJ14,
against air.IJ16, IJ20, IJ22,
The nozzle firing isIJ23, IJ24, IJ25,
usually performedIJ26, IJ27, IJ28,
during a specialIJ29, IJ30, IJ31,
clearing cycle, afterIJ32, IJ33, IJ34,
first moving the printIJ36, IJ37, IJ38,
head to a cleaningIJ39, IJ40,, IJ41,
station.IJ42, IJ43, IJ44,,
IJ45
ExtraIn systems which heatCan be highlyRequires higherSilverbrook, EP
power tothe ink, but do not boileffective if thedrive voltage for0771 658 A2 and
ink heaterit under normalheater is adjacent toclearingrelated patent
situations, nozzlethe nozzleMay requireapplications
clearing can belarger drive
achieved by over-transistors
powering the heater
and boiling ink at the
nozzle.
RapidThe actuator is fired inDoes not requireEffectivenessMay be used
successionrapid succession. Inextra drive circuitsdependswith: IJ01, IJ02,
of actuatorsome configurations,on the print headsubstantially uponIJ03, IJ04, IJ05,
pulsesthis may cause heatCan be readilythe configuration ofIJ06, IJ07, IJ09,
build-up at the nozzlecontrolled andthe ink jet nozzleIJ10, IJ11, IJ14,
which boils the ink,initiated by digitalIJ16, IJ20, IJ22,
clearing the nozzle. InlogicIJ23, IJ24, IJ25,
other situations, it mayIJ27, IJ28, IJ29,
cause sufficientIJ30, IJ31, IJ32,
vibrations to dislodgeIJ33, IJ34, IJ36,
clogged nozzles.IJ37, IJ38, IJ39,
IJ40, IJ41, IJ42,
IJ43, IJ44, IJ45
ExtraWhere an actuator isA simpleNot suitableMay be used
power tonot normally driven tosolution wherewhere there is awith: IJ03, IJ09,
ink pushingthe limit of its motion,applicablehard limit toIJ16, IJ20, IJ23,
actuatornozzle clearing may beactuator movementIJ24, IJ25, IJ27,
assisted by providingIJ29, IJ30, IJ31,
an enhanced driveIJ32, IJ39, IJ40,
signal to the actuator.IJ41, IJ42, IJ43,
IJ44, IJ45
AcousticAn ultrasonic wave isA high nozzleHighIJ08, IJ13, IJ15,
resonanceapplied to the inkclearing capabilityimplementation costIJ17, IJ18, IJ19,
chamber. This wave iscan be achievedif system does notIJ21
of an appropriateMay bealready include an
amplitude andimplemented at veryacoustic actuator
frequency to causelow cost in systems
sufficient force at thewhich already
nozzle to clearinclude acoustic
blockages. This isactuators
easiest to achieve if
the ultrasonic wave is
at a resonant
frequency of the ink
cavity.
NozzleA microfabricatedCan clearAccurateSilverbrook, EP
clearingplate is pushed againstseverely cloggedmechanical0771 658 A2 and
platethe nozzles. The platenozzlesalignment isrelated patent
has a post for everyrequiredapplications
nozzle. A post movesMoving parts are
through each nozzle,required
displacing dried ink.There is risk of
damage to the
nozzles
Accurate
fabrication is
required
InkThe pressure of the inkMay be effectiveRequiresMay be used
pressureis temporarilywhere otherpressure pump orwith all IJ series ink
pulseincreased so that inkmethods cannot beother pressurejets
streams from all of theusedactuator
nozzles. This may beExpensive
used in conjunctionWasteful of ink
with actuator
energizing.
Print headA flexible ‘blade’ isEffective forDifficult to use ifMany ink jet
wiperwiped across the printplanar print headprint head surface issystems
head surface. Thesurfacesnon-planar or very
blade is usuallyLow costfragile
fabricated from aRequires
flexible polymer, e.g.mechanical parts
rubber or syntheticBlade can wear
elastomer.out in high volume
print systems
SeparateA separate heater isCan be effectiveFabricationCan be used with
ink boilingprovided at the nozzlewhere other nozzlecomplexitymany IJ series ink
heateralthough the normalclearing methodsjets
drop e-ectioncannot be used
mechanism does notCan be
require it. The heatersimplemented at no
do not requireadditional cost in
individual drivesome ink jet
circuits, as manyconfigurations
nozzles can be cleared
simultaneously, and no
imaging is required.

NOZZLE PLATE CONSTRUCTION
DescriptionAdvantagesDisadvantagesExamples
ElectroformedA nozzle plate isFabricationHighHewlett Packard
nickelseparately fabricatedsimplicitytemperatures andThermal Ink jet
from electroformedpressures are
nickel, and bonded torequired to bond
the print head chip.nozzle plate
Minimum
thickness constraints
Differential
thermal expansion
LaserIndividual nozzleNo masksEach hole mustCanon Bubblejet
ablated orholes are ablated by anrequiredbe individually1988 Sercel et
drilledintense UV laser in aCan be quite fastformedal., SPIE, Vol. 998
polymernozzle plate, which isSome controlSpecialExcimer Beam
typically a polymerover nozzle profileequipment requiredApplications, pp.
such as polyimide oris possibleSlow where there76-83
polysulphoneEquipmentare many thousands1993 Watanabe
required is relativelyof nozzles per printet al., U.S. Pat. No.
low costhead5,208,604
May produce thin
burrs at exit holes
SiliconA separate nozzleHigh accuracy isTwo partK. Bean, IEEE
micromachinedplate isattainableconstructionTransactions on
micromachined fromHigh costElectron Devices,
single crystal silicon,RequiresVol. ED-25, No. 10,
and bonded to theprecision alignment1978, pp 1185-1195
print head wafer.Nozzles may beXerox 1990
clogged by adhesiveHawkins et al., U.S. Pat. No.
4,899,181
GlassFine glass capillariesNo expensiveVery small1970 Zoltan U.S. Pat. No.
capillariesare drawn from glassequipment requirednozzle sizes are3,683,212
tubing. This methodSimple to makedifficult to form
has been used forsingle nozzlesNot suited for
making individualmass production
nozzles, but is difficult
to use for bulk
manufacturing of print
heads with thousands
of nozzles.
Monolithic,The nozzle plate isHigh accuracyRequiresSilverbrook, EP
surfacedeposited as a layer(<1 μm)sacrificial layer0771 658 A2 and
micromachinedusing standard VLSIMonolithicunder the nozzlerelated patent
using VLSIdeposition techniques.Low costplate to form theapplications
litho-Nozzles are etched inExistingnozzle chamberIJ01, IJ02, IJ04,
graphicthe nozzle plate usingprocesses can beSurface may beIJ11, IJ12, IJ17,
processesVLSI lithography andusedfragile to the touchIJ18, IJ20, IJ22,
etching.IJ24, IJ27, IJ28,
IJ29, IJ30, IJ31,
IJ32, IJ33, IJ34,
IJ36, IJ37, IJ38,
IJ39, IJ40, IJ41,
IJ42, IJ43, IJ44
Monolithic,The nozzle plate is aHigh accuracyRequires longIJ03, IJ05, IJ06,
etchedburied etch stop in the(<1 μm)etch timesIJ07, IJ08, IJ09,
throughwafer. NozzleMonolithicRequires aIJ10, IJ13, IJ14,
substratechambers are etched inLow costsupport waferIJ15, IJ16, IJ19,
the front of the wafer,No differentialIJ21, IJ23, IJ25,
and the wafer isexpansionIJ26
thinned from the back
side. Nozzles are then
etched in the etch stop
layer.
No nozzleVarious methods haveNo nozzles toDifficult toRicoh 1995
platebeen tried to eliminatebecome cloggedcontrol dropSekiya et al U.S. Pat. No.
the nozzles entirely, toposition accurately5,412,413
prevent nozzleCrosstalk1993 Hadimioglu
clogging. Theseproblemset al EUP 550,192
include thermal bubble1993 Elrod et al
mechanisms andEUP 572,220
acoustic lens
mechanisms
TroughEach drop ejector hasReducedDrop firingIJ35
a trough throughmanufacturingdirection is sensitive
which a paddle moves.complexityto wicking.
There is no nozzleMonolithic
plate.
Nozzle slitThe elimination ofNo nozzles toDifficult to1989 Saito et al
instead ofnozzle holes andbecome cloggedcontrol dropU.S. Pat. No. 4,799,068
individualreplacement by a slitposition accurately
nozzlesencompassing manyCrosstalk
actuator positionsproblems
reduces nozzle
clogging, but increases
crosstalk due to ink
surface waves

DROP EJECTION DIRECTION
DescriptionAdvantagesDisadvantagesExamples
EdgeInk flow is along theSimpleNozzles limitedCanon Bubblejet
(‘edgesurface of the chip,constructionto edge1979 Endo et al GB
shooter’)and ink drops areNo siliconHigh resolutionpatent 2,007,162
ejected from the chipetching requiredis difficultXerox heater-in-
edge.Good heatFast colorpit 1990 Hawkins et
sinking via substrateprinting requiresal U.S. Pat. No. 4,899,181
Mechanicallyone print head perTone-jet
strongcolor
Ease of chip
handing
SurfaceInk flow is along theNo bulk siliconMaximum inkHewlett-Packard
(‘roofsurface of the chip,etching requiredflow is severelyTIJ 1982 Vaught et
shooter’)and ink drops areSilicon can makerestrictedal U.S. Pat. No. 4,490,728
ejected from the chipan effective heatIJ02, IJ11, IJ12,
surface, normal to thesinkIJ20, IJ22
plane of the chip.Mechanical
strength
ThroughInk flow is through theHigh ink flowRequires bulkSilverbrook, EP
chip,chip, and ink drops areSuitable forsilicon etching0771 658 A2 and
forwardejected from the frontpagewidth printrelated patent
(‘upsurface of the chip.headsapplications
shooter’)High nozzleIJ04, IJ17, IJ18,
packing densityIJ24, IJ27-IJ45
therefore low
manufacturing cost
ThroughInk flow is through theHigh ink flowRequires waferIJ01, IJ03, IJ05,
chip,chip, and ink drops areSuitable forthinningIJ06, IJ07, IJ08,
reverseejected from the rearpagewidth printRequires specialIJ09, IJ10, IJ13,
(‘downsurface of the chip.headshandling duringIJ14, IJ15, IJ16,
shooter’)High nozzlemanufactureIJ19, IJ21, IJ23,
packing densityIJ25, IJ26
therefore low
manufacturing cost
ThroughInk flow is through theSuitable forPagewidth printEpson Stylus
actuatoractuator, which is notpiezoelectric printheads requireTektronix hot
fabricated as part ofheadsseveral thousandmelt piezoelectric
the same substrate asconnections to driveink jets
the drive transistors.circuits
Cannot be
manufactured in
standard CMOS
fabs
Complex
assembly required

INK TYPE
DescriptionAdvantagesDisadvantagesExamples
Aqueous,Water based ink whichEnvironmentallySlow dryingMost existing ink
dyetypically contains:friendlyCorrosivejets
water, dye, surfactant,No odorBleeds on paperAll IJ series ink
humectant, andMayjets
biocide.strikethroughSilverbrook, EP
Modern ink dyes haveCockles paper0771 658 A2 and
high water-fastness,related patent
light fastnessapplications
Aqueous,Water based ink whichEnvironmentallySlow dryingIJ02, IJ04, IJ21,
pigmenttypically contains:friendlyCorrosiveIJ26, IJ27, IJ30
water, pigment,No odorPigment maySilverbrook, EP
surfactant, humectant,Reduced bleedclog nozzles0771 658 A2 and
and biocide.Reduced wickingPigment mayrelated patent
Pigments have anReducedclog actuatorapplications
advantage in reducedstrikethroughmechanismsPiezoelectric ink-
bleed, wicking andCockles paperjets
strikethrough.Thermal ink jets
(with significant
restrictions)
MethylMEK is a highlyVery fast dryingOdorousAll IJ series ink
Ethylvolatile solvent usedPrints on variousFlammablejets
Ketonefor industrial printingsubstrates such as
(MEK)on difficult surfacesmetals and plastics
such as aluminum
cans.
AlcoholAlcohol based inksFast dryingSlight odorAll IJ series ink
(ethanol, 2-can be used where theOperates at sub-Flammablejets
butanol,printer must operate atfreezing
and others)temperatures belowtemperatures
the freezing point ofReduced paper
water. An example ofcockle
this is in-cameraLow cost
consumer
photographic printing.
PhaseThe ink is solid atNo drying time-High viscosityTektronix hot
changeroom temperature, andink instantly freezesPrinted inkmelt piezoelectric
(hot melt)is melted in the printon the print mediumtypically has aink jets
head before jetting.Almost any print‘waxy’ feel1989 Nowak
Hot melt inks aremedium can be usedPrinted pagesU.S. Pat. No. 4,820,346
usually wax based,No paper cocklemay ‘block’All IJ series ink
with a melting pointoccursInk temperaturejets
around 80° C. AfterNo wickingmay be above the
jetting the ink freezesoccurscurie point of
almost instantly uponNo bleed occurspermanent magnets
contacting the printNo strikethroughInk heaters
medium or a transferoccursconsume power
roller.Long warm-up
time
OilOil based inks areHigh solubilityHigh viscosity:All IJ series ink
extensively used inmedium for somethis is a significantjets
offset printing. Theydyeslimitation for use in
have advantages inDoes not cockleink jets, which
improvedpaperusually require a
characteristics onDoes not wicklow viscosity. Some
paper (especially nothrough papershort chain and
wicking or cockle).multi-branched oils
Oil soluble dies andhave a sufficiently
pigments are required.low viscosity.
Slow drying
MicroemulsionA microemulsion is aStops ink bleedViscosity higherAll IJ series ink
stable, self formingHigh dyethan waterjets
emulsion of oil, water,solubilityCost is slightly
and surfactant. TheWater, oil, andhigher than water
characteristic drop sizeamphiphilic solublebased ink
is less than 100 nm,dies can be usedHigh surfactant
and is determined byCan stabilizeconcentration
the preferred curvaturepigmentrequired (around
of the surfactant.suspensions5%)