DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

[0028] Referring now to one embodiment of the present invention as depicted in FIG. 1 ( a ), a flexible optoelectronic circuit 100 is deposited on a substrate 110 by way of a release layer 112 . The release layer 112 permits releasing the circuit 100 from the substrate 110 . It will be understood by those having ordinary skill in the art that when a layer or element is “deposited on” another layer or element, it may be formed directly on top, bottom or side surface area, or one or more intervening layers may be provided between the layers.

[0029] The optoelectronic circuit 100 comprises a first insulating layer 116 , a second insulating layer 118 including an optical element 120 formed therein, and a third insulating layer 122 deposited on the optical element 120 and second insulating layer 118 . In this embodiment, insulating layers 116 , 118 , 122 comprise one or more organic dielectric materials, selected for their compatibility to manufacturing processes and for their optical properties, discussed in more detail below. The optoelectronic circuit 100 is deposited upon a substrate 110 by way of the release layer 112 . According to one embodiment, the substrate 110 comprises a semiconductor and the release layer 112 comprises a semiconductor oxide layer. Alternatively, the flexible optoelectronic circuit may be formed on an adequate surface, such as ceramic, quartz, or glass, and a corresponding release layer provided matching the material characteristics of the substrate and permitting fabrication and release.

[0030] FIG. 1 ( b ) represents the flexible optoelectronic circuit 100 having been released from the substrate 110 and therefore independent of a substrate. The release layer has been removed from the first insulating layer 116 and the substrate 110 . Methods and techniques for removing release layers commensurate with particular materials may be used, and one example is described more fully below. As the layers and components have been released from the substrate, a flexible optoelectronic circuit 100 independent of a substrate 110 is thereby provided.

[0031] As is also depicted in FIGS. 1 ( a ) and 1 ( b ), one embodiment of the flexible optoelectronic circuit 100 includes at least one conductive layer 124 deposited on an insulating layer 116 . The conductive layer 124 is typically formed of conductive materials generally used in flexible circuits, preferably metal, such as copper, platinum, gold, aluminum, etc. As is known to one of ordinary skill in the art, the conductive layer 124 may be employed in electronic circuits and electronic elements within the flexible circuit 100 . Accordingly, the conductive layer 124 is selected according to desired electronic circuit elements and components requirements.

[0032] Typically, it is desirable to provide a conductive layer 124 in communication with back contacts 130 , 132 on the flexible circuit 100 formed within the first insulating layer 116 . As such, these contacts 130 , 132 are in electrical connectivity with conducting elements deposited on the first insulating layer 116 of the optoelectronic circuit 100 . In the one embodiment shown in FIGS. 1 ( a ) and 1 ( b ), electrical connectivity between the contacts 130 , 132 and the conductive elements are achieved by depositing electrical vias 126 , 128 within the first insulating layer 116 . In this embodiment, conductive patterns within the first insulating layer 116 , and any similarly desired patterns within the second or third insulating layers 118 , 122 are deposited according to desired via routing and generally deposited according to the specific application requirements of the flexible circuit.

[0033] In one advantageous embodiment, the flexible insulating layers 116 , 118 , 122 comprise dielectric organic material deposited in layers. The organic materials used in this embodiment are chosen according to a relatively lower refractive index in comparison to the optical elements 120 , discussed in more detail below. Some specific materials that are used in this embodiment include organic materials from the families of benzocyclobutenes (BCB), polyimides, or polyfluorinatedcyclobutenes and other aryl ether polymers containing perfluorocyclobutyl linkages, hereinafter referred to as PFCB.

[0034] The one or more optical elements 120 , generally waveguides, are also typically organic materials and include materials from the families of BCBs, polyimides, or PFCBs. As such, the optical element material is selected according to its index of refraction in relationship to the indices of refraction of the material forming the insulating layers 116 . When the index of refraction of the optical element 120 is higher than that of the insulating layers 116 , 118 , 122 , an optical ray propagating through the optical element 120 will be internally reflected when at an angle of incidence greater than the critical angle determined by the respective indices of refraction, thereby forming a waveguide. For example, a transparent material may be chosen to form the waveguide. The insulating layers 116 , 118 , 122 , which are deposited on the optical elements 120 , are chosen to have correspondingly lower indices of refraction in order to act as a cladding for the waveguide.

[0035] Additionally, the insulating layers and optical elements may include photoimagable organic material, selected from the above groups, which permits imaging. Such materials may be used, as required, in order to define additional structures, optical and electrical, deposited on layers of the flexible optoelectronic circuit. Typically, these structures are defined by monolithic fabrication techniques, such as photolithography. As such, the resulting elements generally have a feature size of about 5 μm to about 50 μm. Therefore, the feature size of the elements permits a higher density optoelectronic circuit (i.e., a greater number of elements deposited within a single layer), and provides for multiple layers, while maintaining desired physical properties, such as flexibility, size, etc.

[0036] FIGS. 2 ( a ) and 2 ( b ) illustrate a cross sectional view of such an alternate embodiment of the flexible optoelectronic circuit 200 , also deposited on and independent of a substrate 210 . In this embodiment, an optical element 220 is deposited on the first insulating layer 216 independently of the second insulating layer 216 . The second insulating layer 218 is deposited on the optical element encompassing the portion not contacting the first insulating layer 216 . Therefore, the requirement of an additional insulating layer is obviated. An advantageous material for the insulating layers 216 , 218 in this embodiment also includes photoimagable BCBs, polyimides, and PFCBs. The optical material is selected such that the corresponding index of refraction is higher than that of the index of refraction of the insulating layers 216 .

[0037] FIGS. 2 ( a ) and 2 ( b ) also depict a conductive layer 224 , back contacts 230 , 232 , and electrical vias 226 , 228 . The conductive layer 224 is typically formed of conductive materials generally used in flexible circuits, as in the previously described embodiment. Similarly, the conductive layer 224 may be employed in electronic circuits and electronic elements within the flexible circuit 200 . Accordingly, the conductive layer 224 is selected according to desired electronic circuit elements and components requirements.

[0038] The optoelectronic circuit 200 is deposited upon a substrate 210 having a release layer 212 . The release layer 212 permits releasing the circuit 200 from the substrate 210 . According to one embodiment, the substrate and release layer comprise a semiconductor and semiconductor oxide layer, respectively. In FIG. 2 ( b ) the flexible optoelectronic circuit 200 has been released from the substrate 210 and is therefore independent of a substrate. According to another embodiment, the substrate and release layer comprise a ultraviolet light transparent substrate, such as glass or quartz, and an ultraviolet light sensitive adhesive. The release layer has been removed from the first insulating layer 216 and the substrate 210 . Methods and techniques for removing release layers commensurate with particular materials are used, and one example is described more fully below. As the layers and components have been released from a substrate, a flexible optoelectronic circuit independent of a substrate is thereby provided.

[0039] Desired circuit elements, including electronic, optical, and optoelectronic elements may be deposited with the flexible optoelectronic circuits of the present invention. The optical elements typically comprise waveguides. As is known to those skilled in the art, waveguides are therefore deposited in spatial relationships with other waveguides and/or other devices to form passive or active optoelectronic elements, such as directional couplers, Y-splitters, diffraction gratings, optical filters, Bragg gratings, modulators, etc. Therefore, optical patterns and conductor patterns defined on insulating layers throughout the flexible optoelectronic circuit are specifically designed to obtain certain desired elements.

[0040] For example, FIG. 3 illustrates an orthographic cross section view of an optoelectronic circuit 300 having a waveguide and a conductive layer 324 . In this regard, FIG. 3 is a relatively simplistic layout for illustration purposes. The optical pattern defines a Y-splitter 320 , in which the optical material forms a waveguide and permits splitting an optical signal to two separate paths. As such, the optical pattern for a splitter 320 is necessarily defined within the second insulating layer 316 . Additionally, simple electronic interconnection circuit is also depicted. A microstrip line 320 is provided comprising a conductive layer. The microstrip 324 is in communication with each of the back contacts 330 , 332 by way of the vias 326 , 328 .

[0041] Similarly, FIGS. 1 through 3 are examples of relatively simplistic configurations and related optic and electrical connectivities. It should be noted that other fabrication configurations and electrical connectives are also feasible and are within the inventive concepts disclosed herein. The specific configuration and connectivity will be chosen to best match the performance requirements of a particular application. The flexible optoelectronic circuit of the present invention is generally fabricated using standard semiconductor manufacturing techniques. The flexible optoelectronic circuit is deposited on a substrate by way of a release layer and subsequently released from the substrate, thus the flexible circuit is independent of a substrate.

[0042] Having described embodiments of the flexible optoelectronic circuit, it is appropriate to now turn to an advantageous method for forming the flexible optoelectronic circuit. Therefore, as described herein, the manufacturing of the flexible optoelectronic circuit is demonstrated by example with respect to standard monolithic semiconductor manufacturing techniques, including chemical vapor phase deposition (CVD) techniques, physical vapor deposition or sputtering techniques, metal evaporation techniques, metal plating techniques (electroplating and electroless plating), spin-on deposition techniques, photolithography, and wet or dry etching techniques. The specific deposition technique is often chosen with respect to manufacturing equipment and materials used in the deposition. As such, the inventive principles discussed herein may be used in conjunction with many techniques and materials, as will be recognized by one of ordinary skill in the art. Some specific materials compatible with these techniques have been identified and include materials related to the families of semiconductors, semiconductor oxides, BCBs, polyimides, PFCBs, conductive films, and resistive films.

[0043] FIGS. 4 ( a ) through 4 ( h ) illustrate one advantageous method of forming a flexible optoelectronic circuit. Starting with FIG. 4 ( a ), the flexible optoelectronic circuit is formed on a substrate 410 having a release layer 412 . Typically, the substrate 410 comprises a semiconductor material. The release layer is generally an oxide layer on the semiconductor material. An oxide layer may be grown by methods of wet or dry oxide reaction with the semiconductor substrate. Alternatively, an oxide layer may be deposited via CVD techniques. An oxide release layer is particularly well suited for providing a release layer due to the availability of commercially accepted etching methods for removing the release layer. Alternative substrates and release layers particularly suited to etching techniques will also be recognized by one of ordinary skill in the art and can be substituted accordingly.

[0044] As shown in FIG. 4 ( b ), deposited on the release layer 412 are back contacts 430 , 432 for the flexible optoelectronic circuit. Typically, it is desirable to provide back contacts 430 , 432 on the flexible circuit formed within the first insulating layer 416 . Therefore, the contacts 430 , 432 are typically conductive thin films deposited and patterned by standard monolithic deposition and etching techniques. Such techniques are known to one of ordinary skill in the art and include using one or more photoresists, and a series of imaging, curing, and etching steps as is appropriate for the particular conductive material being used to form the contacts 430 , 432 .

[0045] The first insulating layer 416 is deposited on the release layer 412 . The first insulating layer advantageously comprises a BCB, polyimide, or PFCB, and more advantageously a photoimagable BCB, polyimide, or PFCB. As such, these exemplary photoimagable organic materials permit image curing and etching specific optical and electrical patterns for use in depositing subsequent layers. In this regard, the first insulating layer 416 is also deposited using a common deposition technique, such as spin-on deposition, stencil, and screen print techniques, as are known to those skilled in the art.

[0046] Generally, the contacts 430 , 432 are in electrical connectivity with conductive elements deposited on the first insulating layer 416 or subsequent insulating layers of the optoelectronic circuit. A conductive layer may be deposited directly on the contacts 430 , 432 or, as is more often the case, deposited in electrical connectivity through electrical vias. FIG. 4 ( c ) illustrates vias 426 , 428 deposited through the first insulating layer 416 . Again, one or more photoresists are deposited imaged, cured, and etched as is appropriate for the particular insulating layer material and the conductive material deposited for the vias 426 , 428 .

[0047] Subsequently, FIG. 4 ( d ) illustrates a conductive layer 424 deposited on the vias and first insulating layer 416 and patterned as desired using same monolithic manufacturing techniques. The conductive layer 424 material is selected according to the desired electronic elements and components that may be incorporated into the flexible optoelectronic circuit. These may include films that are commonly used in flexible circuit electronic elements and components, such as conductive thin films and resistive thin films.

[0048] FIG. 4 ( d ) also depicts a second insulating layer 418 deposited on the conductive layer 424 and the first insulating layer 416 . In this example, the second insulating layer 418 is a photoimagable organic material, such as a photoimagable BCB or polyimide. As such, the techniques used to deposit the second insulating layer 418 are substantially the same as those used to deposit the first insulating layer 416 .

[0049] Referring now to FIG. 4 ( e ), a pattern may be defined within the second insulating layer 418 by means of photolithography and etching. This is represented in FIG. 4 ( e ) by the recess within the second insulating layer 418 . In this regard, the patterns are etched in order to define optical patterns subsequently filled with an optical waveguiding material, discussed in more detail below.

[0050] As illustrated in FIG. 4 ( f ), optical material, typically a transparent organic material, such as BCB, polyimide, or PFCB, is then chosen to fill the optical pattern forming the optical element 420 , a waveguide. As with previous layers of BCB, polyimide, or PFCB, similar deposition techniques compatible with the desired optical material may be used, as in the above steps. The specific material selected for the optical elements, however, must be carefully selected to ensure that the optical element 420 operates as a waveguide. The optical element material is selected according to its index of refraction in relationship to the indices of refraction of the material forming the insulating layers 416 , 418 , 422 . When the index of refraction of the optical element 420 is higher than that of the insulating layers 416 , 418 , 422 , an optical ray propagating through the optical element 420 will be internally reflected when at an angle of incidence greater than the critical angle determined by the respective indices of refraction, thereby forming a waveguide.

[0051] As depicted in FIG. 4 ( g ), deposited on the optical element 420 and the second insulating layer 418 is a third insulating layer 422 , which is also selected from the families of BCBs, polyimides, and PFCBs. As such, the third insulating layer 422 is deposited in substantially the same manner as the first and second insulating layer.

[0052] Subsequently, additional conductive layers and conductive elements, optical elements and insulating layers may be similarly deposited on the previously described layers. Additionally, the disclosure herein illustrates a relatively simple layer depicting minimal conductive elements and optical elements, however, it is expected that multiple optical and conductive elements will be deposited within a single layer, and multiple layers optical and conductive elements will be repeatedly designed and deposited upon other layers. The number of elements within a layer and the number of layers themselves are only constrained by the available manufacturing parameters, such as size requirements for the imaging and etching techniques, the area of the semiconductor substrate, and by the physical dimension limitations set for the circuit by the intended application of the circuit.

[0053] Referring to FIG. 4 ( h ), upon completing formation of the optoelectronic circuit elements and layers, the layers and circuit elements are released from the substrate 410 . One embodiment of releasing the circuit comprises etching the release layer 412 , such as when the release layer is an oxide layer. Etching comprises any etching technique from the families of wet and dry etching techniques appropriate for etching compatible with the release layer and ease of manufacture. These etching techniques are known to one of ordinary skill in the art and will become apparent with respect to the selection of a desired material for the substrate and corresponding release layer. The resulting circuit is therefore a flexible optoelectronic circuit 400 .

[0054] Another embodiment of releasing the optoelectronic circuit comprises exposing the release layer 412 to ultraviolet light, such as when the release layer is an ultraviolet sensitive adhesive. In this case, the release layer is formed on a substrate 410 , which is transparent to ultraviolet light, such as glass or quartz. The flexible optoelectronic circuit 400 is formed on the adhesive release layer in accordance with the foregoing discussion. After forming the flexible optoelectronic circuit, the adhesive is exposed to ultraviolet light through the transparent substrate. Once the release layer is exposed to ultraviolet light, the adhesiveness is deactivated and the optoelectronic circuit 400 is released from and independent of the substrate.

[0055] It should be noted that while the embodiments described herein appears to provide for specific layering, i.e., constructing an insulating layer prior to a conductive layer or an insulating layer prior to an optical element, it is possible to process the layering of the device in any order that makes for efficient and reliable manufacturing. In other words, it is possible and within the inventive concepts herein disclosed to fabricate the device with either the conductive layers being deposited and patterned, and then insulating layers deposited thereon, or vice versa, or combinations of each.

[0056] For example, FIGS. 5 ( a ) through 5 ( f ) illustrate such an alternate method of forming an optical element independent of any pattering and etching of a recess in an insulating layer. In this embodiment, the release layer 512 , the first insulating layer 516 back contacts 530 , 532 , and vias 526 , 528 , are all formed substantially similar to the steps described above, as shown in FIGS. 5 ( a ) through 5 ( c ). However, referring to FIG. 5 ( d ), the optical element 520 is formed without respect to defining an image in the first insulating layer. Rather, the optical element 520 is deposited in a layer and subsequently imaged and etched to define the element deposited upon the first insulating layer. The second insulating 518 layer is likewise deposited over the conductive layer 524 and the optical element 520 forming an optoelectronic flexible circuit 500 . Therefore, the need for a third insulating layer has been obviated.

[0057] As will be recognized by one of ordinary skill in the art, the steps described herein are of general reference to one or more steps and substeps required to achieve desired layering and circuit configurations, particularly with respect to photolithography, deposition of material, and etching. These additional steps vary depending on the specific methods selected to achieve the foregoing steps, however, one of ordinary skill in the art will recognize the required steps and substeps upon choosing the best techniques which are efficient and available for manufacturing the flexible optoelectronic circuit disclosed herein. Therefore, additional steps will generally be required with respect any one of these methods, and will be easily recognized by one of ordinary skill in the art.

[0058] These specific examples address advantageous embodiments of the present invention. In this regard, FIGS. 4 and 5 are examples of relatively simplistic configurations and related optic and electrical connectivities for illustration purposes. It is expected that more complex electrical and optical connectivities and elements will be desired when implementing the concepts of this invention, and these complex structures are known and will become apparent to one of ordinary skill in the art. Although not specifically addressed herein, other fabrication techniques such as inkjet deposition, screen printing, and roll-to-roll processing may also be implemented in accordance with the present invention with compatible materials without departing from the scope or spirit of the present invention.

[0059] Many modifications and other embodiments of the invention will come to mind to one of ordinary skill in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.