DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] The aforementioned problem results from the presence of an interface between the sensor substrate and the air. Therefore, the above-mentioned problem can be solved by eliminating such interface, because the reflection at the interface is eliminated. The present inventors have therefore investigated various configurations and have found a configuration which allows to substantially eliminate such interface. More specifically, if the light entering the sensor substrate can vanish by absorption before reaching the interface, the interface becomes substantially absent for such entering light, so that the reflection does not take place and the above-mentioned problem can be solved.

[0058] In the following, the present invention for realizing the above principle will be explained in detail, with reference to the attached drawings. The image reading device of the present invention is advantageously applied to the image reading device for an X-ray image pick-up apparatus. However, the application of the image reading device of the present invention is not limited to the X-ray image pick-up apparatus, and it is possible to also apply the image reading device of the present invention to the radiation image pick-up apparatus utilizing α-ray, β-ray or γ-ray other than X-ray.

[EXAMPLE 1]

[0059] FIG. 1 is a cross-sectional view of an image reading device of the present invention, for use in an X-ray image pick-up apparatus.

[0060] The image reading device for X-ray image pick-up apparats as shown in FIG. 1 is an image reading device including a sensor substrate having a photosensor S, a thin film transistor T and the like. Reference numeral 101 indicates the sensor substrate; 102 , a gate electrode; 103 , a first electrode; 104 , a gate insulating film; 105 , a semiconductor layer; 106 , an impurity layer; 107 , a drain electrode; 108 , a source electrode; 109 , a passivation layer; 110 , a fluorescent plate; X, X-ray.

[0061] A radiation X (X-ray in this case) is detected by the combination of a fluorescent plate 110 and a photosensor S. The X-ray X entered from the exterior to the fluorescent plate is converted therein into the light of a wavelength region (visible light in this case) detectable with the photosensor. The light reaches the photosensor in the size of 1×magnification and is converted by the photosensor into a photocurrent. In the present example, the sensor substrate 101 is composed of a colored glass. The fluorescent plate 110 in the present example was mainly composed of Gd ₂ 0 ₂ S:Tl ³⁺ , and the emitted light included the light with the largest intensity which was the green light of a wavelength λ=550 nm. In the present example, therefore, the image reading device was produced by employing a red-colored glass substrate and forming photosensors, thin film transistors, capacitance elements and the like. thereon. The method of producing the image reading device is basically same as that in the conventional method as explained in the foregoing.

[0062] The glass was composed of an ordinary glass material colored with Au, Cu, Se or Cd (S, Se), but such coloring elements did not have any adverse effect on the elements formed on the colored glass.

[0063] FIGS. 2A and 2B schematically show the experiments conducted for confirming the effect of the present invention, wherein FIG. 2A shows a case of employing an ordinary glass plate while FIG. 2B shows a case of employing a red-colored glass plate as in the present example. The refractive index of the glass substrate was set as 1.5 in both cases. The effect was confirmed by measuring the spectral sensitivity of the magnitude of the normal reflectance of light on the red-colored glass 202 and the ordinary glass 201 with respect to the incident light. In case of the ordinary glass, the light reflection takes place at the first interface K 1 and the second interface K 2 as shown in FIG. 2A . More specifically, the incident light L is at first reflected at the first interface K 1 , and a part of the incident light is further reflected at the second interface K 2 .

[0064] FIG. 3 is a reflectance-wavelength characteristic graph, in which black circles (a) show the characteristics in use of the ordinary glass. As shown by black circles (a), the reflectance remains almost flat from about 700 nm to 350 nm, but decreases to about a half starting from about 350 nm. This is because the glass substrate starts to absorb light from about 350 nm and is almost opaque at about 300 nm.

[0065] Therefore, the light in this wavelength region does not reach the second interface K 2 , so that the reflection does not take place at the second interface but only at the first interface.

[0066] On the other hand, in use of the red-colored glass substrate opaque to the green light, the reflection at the second interface K 2 is substantially suppressed from about 600 nm, as shown by open circles (b) in FIG. 3 .

[0067] As be apparent from the foregoing experiments, in case of employing the red-colored glass substrate, the green light having the peak at 550 nm is absorbed in the substrate before reaching the second interface K 2 .

[0068] Therefore, in the present example employing the red-colored glass substrate for the sensor substrate, the green light having the peak at 550 nm and entering the sensor substrate is absorbed within the substrate before reaching the second interface K 2 , so that the reflection at the second interface K 2 does not take place.

[0069] Consequently there can be attained the object of the present invention of substantially eliminating the reflection at the second interface K 2 in the wavelength region sensitive to the photosensor.

[0070] The optical crosstalk was compared by employing the substrate of the present example in the actual image reading device. A light shielding mask was placed on a part of the image reading device, and the sensor outputs in the pixels receiving the light (“LIGHT” region in FIG. 4 ) and the pixels not receiving the light (“DARK” region in FIG. 4 ) were compared by taking the pixel position in the axis of abscissa in FIG. 4 . In FIG. 4 , sample No. 0 corresponds to the pixel under the end of the light shielding mask and sample Nos. 1 to 100 correspond to pixels under the light shielding mask. In FIG. 4 , open symbols (a) show the distribution of results (represented by open squares and open circles) of the conventional image reading device (employing the ordinary glass substrate). The results indicate that the light spreads over the region of 60 to 70 pixels with an output not larger than 1%. On the other hand, in the device of the present example, as indicated by the distribution of black symbols (b) (represented by black squares and black circles), the light spreading is reduced and the output is lowered to 1% or less within about 10 pixels.

[0071] As a result, the image reading device of excellent sharpness could be obtained by the present example.

[0072] Also in the present example, because all the light is absorbed in the sensor substrate, it is no longer necessary to consider, even in case of mounting the sensor substrate on a base member as described in the following examples, the optical influence of such base member or the adhesive material for adhering the sensor substrate and the base member, so that the freedom of designing can be increased.

[0073] The present example employs the red-colored glass substrate because the fluorescent plate emits green light, but such color is not restrictive. There can be employed any material for the substrate as long as it matches the process for forming the photosensors and the like and it has a color complementary to the color of the light emitted by the fluorescent plate. For example, the effect of the present invention can be sufficiently exhibited with black-colored heat-resistant plastic material.

[0074] Also in the manufacturing process, the substrate itself serves as a light absorbing material, so that there is not required a step of reducing the stray light and the image reading device of a large area can be obtained without reducing the production yield by properly managing the substrate.

[EXAMPLE 2]

[0075] FIG. 5A is a schematic plan view of an image reading device of the present invention for use in an X-ray image pick-up apparatus, and FIG. 5B is a cross-sectional view of the device of FIG. 5A .

[0076] As be apparent from FIGS. 5A and 5B , in the present example, the image reading device of a large area is produced by placing a plurality of sensor substrates 503 (four substrates in the present case) on the same base member 501 , which is composed of a low-alkali colored glass. The sensor substrate 503 has almost the same structure as that of the image reading device for X-ray image pick-up apparatus as described in Example 1 referring to FIG. 1 and corresponds to the sensor substrate 101 in FIG. 1 .

[0077] Similarly to Example 1, radiation (X-ray in the present case) is detected by the combination of a fluorescent plate and a photosensor. The X-ray entered from the exterior to the fluorescent plate is converted therein into light of a wavelength region (visible light in the present case) detectable by the photosensor. This light reaches the photosensor in the size of 1×magnification and is converted in the photosensor into a photocurrent.

[0078] The sensor substrate 503 was composed of low-alkali glass with a refractive index of 1.5. The sensor substrate 503 and the base member 501 were adhered with an epoxy-based adhesive 502 . The epoxy resin after curing had a refractive index of 1.4 to 1.6, which is almost the same as that of the sensor substrate. The base member 501 was composed of colored low-alkali glass having the same refractive index as that of the sensor substrate 503 .

[0079] The fluorescent plate P provided on the sensor substrate was mainly composed of Gd ₂ O ₂ S:Tl ³⁺ which emitted the green light of a wavelength λ=550 nm. In the present example, the image reading device was produced by employing a red-colored glass plate as the base member and by adhering glass plates having photosensors, thin film transistors, capacitance elements and the like, that is, the sensor substrate 503 on the base member with the above-mentioned adhesive.

[0080] The same colored glass as that used in Example 1 was used as the base member, and also in the present example the coloring elements employed in the glass as the base did not show any adverse effects on the elements provided on the sensor substrates.

[0081] Similarly to Example 1, FIG. 8A schematically shows the experiment conducted for confirming the effect of the present invention. The glass substrate 803 also had a refractive index of 1.5. The total reflection at the light incident side was measured on a red-colored glass substrate 801 and an ordinary glass 803 mutually adhered with epoxy resin 802 , and on an ordinary glass substrate 801 ′ (not shown) and an ordinary glass 803 mutually adhered with the epoxy resin 802 , and the effect was confirmed by measuring the spectral sensitivity of a magnitude of the normal reflectance of light with respect to the incident light.

[0082] The sensor substrate 803 , adhesive 802 and base member 801 (or 801 ′) which have almost the same refractive index are optically substantially uniform, so that the light entering in the sensor substrate is transmitted through the adhesive and enters the base member 801 (or 801 ′).

[0083] In the conventional configuration (with the ordinary glass), the reflected light takes place at the first interface on the surface of the sensor substrate 803 and at the second interface on the back surface of the base member 801 ′. Therefore, when the light enters, it is reflected at the first interface, and a part of the incident light is further reflected at the second interface. In FIG. 9 , black circles (a) indicate the reflectance-wavelength characteristics in case the ordinary glass is employed as the base member.

[0084] On the other hand, in case the base member 801 is colored red for absorbing the green light, the light entering the base member 801 is absorbed therein before reaching the back surface thereof. As a result, as indicated by open circles (b) in FIG. 9 , the reflectance at the back interface is substantially lowered from about 600 nm to a low wavelength region side, particularly around 550 nm.

[0085] In the present example, because the base member is composed of red-colored glass plate, the green light having the peak at 550 nm and entering in the sensor substrate is absorbed within the base member before reaching the second interface of the base member, so that the reflection does not take place at the second interface.

[0086] Consequently there can be attained the object of the present invention of substantially eliminating the reflection at the second interface in the wavelength region sensitive to the photosensor.

[0087] The optical crosstalk was compared similarly to Example 1 by employing the substrate of the present example in the actual image reading device. In FIG. 12 , open circles (a) show the result of the present example, while black circles (b) show the result of Example 1. In the device of the present example, the light spreading is reduced and the output is lowered to 1% or less within about 10 pixels, similarly to Example 1.

[0088] As a result, the image reading device of excellent sharpness could be obtained in the present example.

[0089] Because all the light is absorbed in the base member, it is no longer necessary to consider the optical influence of the sensor substrate or the adhesive material for adhering the sensor substrate and the base member, so that the freedom of designing can be increased.

[0090] Also the present example allows to reduce the stray light in ideal manner without adopting a special light absorbing layer.

[0091] Also in the manufacturing process, the substrate itself serves as a light absorbing material, so that there is not required a step of reducing the stray light and the image reading device of a large area can be obtained without reducing the production yield by properly managing the substrate.

[0092] The present example employed the red-colored glass substrate because the fluorescent plate emitted green light. However, there can be employed any material for the substrate as long as it can fix the sensor substrate and it has a color complementary to the color of the light emitted by the fluorescent plate.

[0093] The present example is more effective in preventing the reflection, particularly by employing a base member having almost the same refractive index (including the same refractive index) as that of the sensor substrate or the adhesive material, thereby reducing (or completely eliminating) the reflection at the interface between the sensor substrate and the adhesive layer and the interface between the adhesive layer and the base member, in addition to the effect of the present example for preventing the reflection from the back surface of the base member. The glass substrate of a large area is expensive, but for example a black-colored heat-resistant plastic material can sufficiently exhibit the effect of the present invention and is also advantageous as a low-cost material. Additionally, the sensor substrate 503 used in the present example can be colored to obtain more effective antireflection effect.

[EXAMPLE 3]

[0094] FIG. 6 is a cross-sectional view of an image reading device of the present invention for use in an X-ray image pick-up apparatus. As be apparent from FIG. 6 , the present example provides the image reading device of a larger area by placing a plurality of colorless transparent sensor substrates 603 on the same base member 601 similarly to Example 2, and the present example is to realize the effect of the present invention by the surface treatment of the base member 601 .

[0095] The photosensors, thin film transistors and the like formed on the sensor substrate 603 are the same as in Example 1. The detection of radiation is achieved by the combination of a fluorescent plate and a photosensor. The X-ray entered from the exterior into the fluorescent plate P is converted into light therein and the light is detected by the photosensor.

[0096] The sensor substrate 603 was composed of low-alkali glass with a refractive index of 1.5.

[0097] The sensor substrate 603 and the base member 601 were mutually adhered with an epoxy based adhesive 602 . The cured epoxy showed a refractive index of 1.4 to 1.6.

[0098] The base member 601 was composed of low-alkali glass of the same refractive index as that of the sensor substrate 603 . The surface of the base member 601 was treated with acrylic-resin-based black paint 604 .

[0099] At first a large-sized low-alkali glass plate was prepared and the surface thereof was sprayed with acrylic resin based black paint to form a coating thickness of about 30 μm. The coating film was dried for 24 hours, and glass substrates on which the photosensors, thin film transistors and the like were produced in advance were adhered on the glass. The process was simple and did not degrade the production yield of the sensor substrates themselves because the base member could be prepared separately from the sensor substrates.

[0100] Similarly to the foregoing examples, there was conducted an experiment for confirming the effect of the present invention in the present example. FIG. 8B schematically shows the configuration employed for the experiment. The configuration consists of a glass substrate 807 serving as the sensor substrate, an adhesive layer 806 , and a glass substrate serving as the base member 804 which has a black paint layer 805 on the surface thereof.

[0101] The fluorescent plate P in the present example was mainly composed of Gd ₂ O ₂ S:Tl ³⁺ , which emitted the green light of a wavelength λ=550 nm. In the present example, the surface treatment was executed with a black paint containing a coloring material absorbing at least green light (having complementary color of green).

[0102] The base member was composed of glass having a surface experimentally coated with the black paint or ordinary glass, and the effect was confirmed by measuring the spectral sensitivity of a magnitude of the normal reflectance of light at the side of the sensor substrate with respect to the incident light. FIG. 10 is a reflectance-wavelength characteristic graph, in which black circles (a) show the case of using the ordinary glass, while open circles (b) show the case of using the glass with a surface coated with the black paint.

[0103] In the case with the black paint, the light of 700 nm or less is almost absorbed, so that there is almost no reflection on the back surface of the glass substrate 804 .

[0104] In the present example, use of the base member composed of the glass substrate coated with the black paint causes the black paint provided on the surface of the base member to absorb the green light entering in the sensor substrate which has the peak at 550 nm, thereby suppressing the reflection on the back surface (second interface) of the base member.

[0105] The substrate of the present example could be utilized in the actual image reading device to obtain an image reading device of excellent sharpness without optical crosstalk.

[0106] Because the black paint coated on the base member absorbs all the incoming light, the designing can be achieved without considering the optical influence of the base member or the adhesive material adhering the sensor substrate and the base member, so that the freedom of designing can be increased.

[0107] Also in the manufacturing process, by providing the base member with a function of preventing the stray light, there is not required a step of reducing the stray light on the sensor substrate, thereby not making the process of sensor formation complicate and not reducing the production yield. The image reading device of a high performance and a large area can be produced at a low cost by properly managing the base member.

[0108] The present example employs the base member with the black-colored surface treating material in order to absorb the green light emitted from the fluorescent plate, but there can be employed any material for the base member as long as it can fix the sensor substrate and it has a surface treating material with a color complementary to at least the color of the light emitted by the fluorescent plate.

[0109] The present example is more effective in preventing the reflection, particularly by employing the sensor substrate, adhesive material and surface treatment layer of almost the same refractive index (including the same refractive index), thereby reducing (or completely eliminating) the reflection at the interface between the sensor substrate and the adhesive layer or the interface between the adhesive layer and the surface treatment layer, in addition to the effect of the present example for preventing the reflection from the back surface of the base member. The glass substrate of a large area is expensive, but for example when a heat-resistant plastic material is used as the base member and the surface is treated with red or black acrylic-resin-based paint, the effect of the present invention can be sufficiently exhibited and the coated base member is therefore advantageous as a low-cost material. Additionally, the sensor substrate 603 used in the present example can be colored to obtain more effective antireflection effect.

[EXAMPLE 4]

[0110] FIG. 7 is a cross-sectional view of an image reading device of the present invention for use in an X-ray image pick-up apparatus. As be apparent from FIG. 7 , the present example provides the image reading device of a larger area by placing a plurality of colorless transparent sensor substrates 703 on the same base member 701 basically in the same manner as in Example 2. The present example is to realize the effect of the present invention by treating the back surface of the base member 701 .

[0111] The photosensors, thin film transistors and the like formed on the sensor substrate 703 are the same as in Example 1. The detection of radiation is achieved by the combination of a fluorescent plate and a photosensor. The X-ray entering from the exterior into the fluorescent plate P is converted into light therein and the light is detected by the photosensor.

[0112] The sensor substrate 703 was composed of low-alkali glass with a refractive index of 1.5.

[0113] The sensor substrate 703 and the base member 701 were mutually adhered with an epoxy-based adhesive 702 , which had a refractive index of 1.4 to 1.6 after curing.

[0114] The base member 701 was composed of low-alkali glass of the same refractive index as that of the sensor substrate 703 . The back surface of the base member 701 was spray coated with an acrylic-resin-based black paint to form a coating film with a thickness of about 30 μm. The coating film was dried for 24 hours, and glass substrates on which the photosensors, thin film transistors and the like were prepared in advance were adhered thereon. The process was simple and did not degrade the production yield of the sensor substrates themselves because the base member could be prepared separately from the sensor substrates.

[0115] Similarly to the foregoing examples, there was conducted an experiment for confirming the effect of the present invention in the present example. FIG. 8C schematically shows the configuration employed for the experiment. The configuration consists of a glass substrate 810 serving as the sensor substrate, an adhesive layer 809 , and a glass substrate 808 serving as the base member which has a black paint layer 811 as the back surface thereof.

[0116] The fluorescent plate P in the present example was mainly composed of Gd ₂ O ₂ S:Tl ³⁺ , which emitted the green light of a wavelength λ=550 nm. In the present example, the back surface treatment was executed with a black paint containing a coloring material absorbing at least green light (having Complementary color of green).

[0117] The base member was composed of glass having the back surface experimentally coated with the black paint or ordinary glass, and the effect was confirmed by measuring the spectral sensitivity of a magnitude of the normal reflectance of light at the side of the sensor substrate with respect to the incident light. FIG. 11 is a reflectance-wavelength characteristic graph, in which black circles (a) show the case of using the ordinary glass, while open circles (b) show the case of using the glass having the back surface coated with the black paint.

[0118] In the case of coating the back surface of the glass with the black paint, the light of 700 nm or less is almost absorbed, so that there is almost no reflection on the back surface of the glass substrate.

[0119] In the present example, use of the base member composed of the glass substrate having the back surface coated with the black paint causes the black paint on the back surface of the base member to absorb the green light entered in the sensor substrate which has the peak at 550 nm, thereby suppressing the reflection on the back surface (second interface) of the base member.

[0120] The substrate of the present example could be utilized in the actual image reading device to produce an image reading device of excellent sharpness without optical crosstalk.

[0121] Because the black paint applied onto the back surface of the base member absorbs all the incoming light, the designing can be achieved without considering the optical influence of the base member or the adhesive material adhering the sensor substrate and the base member, so that the freedom of designing can be increased.

[0122] Also in the manufacturing process, because the base member itself is provided with the absorbing member, there is not required a step of reducing the stray light on the sensor substrate, and the image reading device of a large area can be produced at a low cost by properly managing the base member.

[0123] The present example employs the base member with the black-colored back surface treating material in order to absorb the green light emitted from the fluorescent plate, but there can be employed any material for the base member as long as it can fix the sensor substrate and it has the back surface treating material with a color complementary to at least the color of the light emitted by the fluorescent plate. There can be employed a red-colored material for the green light similarly to Example 1 or 2.

[0124] The present example is more effective in preventing the reflection, particularly by employing the sensor substrate, adhesive material and surface treatment layer of almost the same refractive index (including the same refractive index), thereby reducing (or completely eliminating) the reflection at the interface between the sensor substrate and the adhesive layer, the interface between the adhesive layer and the base member or the interface between the base member and the back surface treatment layer, in addition to the effect of the present example for preventing the reflection from the back surface of the base member. The glass substrate of a large area is expensive, but for example a base member composed of heat-resistant plastic material and having the back surface treated with a red or black acrylic resin based paint can sufficiently exhibit the effect of the present invention and is therefore advantageous as a low-cost material. Additionally, at least one of the sensor substrate 703 and the base member 701 used in the present example can be colored to enhance the antireflection effect.

[0125] As explained in the foregoing, the present invention could solve the problem resulting from the presence of an interface between the sensor substrate and the air by substantially eliminating such interface, thereby avoiding the reflection at such interface. Also, according to the constitution of the present invention for substantially eliminating the interface, it is possible to obtain the image reading device of a high performance and a large area in a simple manufacturing process without reducing the production yield.