JP2006196496A - Photosensor and image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photosensor where luminescence of an optical source can easily be controlled, a reading image can be made highly minute and an object image can sufficiently be read as a color image, and to provide an image reader to which the photosensor is applied. <P>SOLUTION: In the photosensor, a first double-gate photosensor PSA becoming a light receiving part of the uppermost layer, a second double-gate photosensor PSB becoming a light receiver of an intermediate layer, and a third double-gate photosensor PSC becoming a light receiving part of the lowermost layer, are laminated and formed on one face side of a transparent insulating substrate SUB. Film thickness of the semiconductor layer 11a of the first double-gate photosensor PSA is set to 50 nm, that of a semiconductor layer 11b of the second double-gate photosensor PSB to 150 nm, and that of a semiconductor layer 11c of the third double-gate photosensor PSC to 300 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photosensor and an image reading apparatus, and more particularly to a photosensor that can read a subject image as a color image and an image reading apparatus to which the photosensor is applied.

  2. Description of the Related Art Conventionally, as an image reading apparatus that reads a subject image such as a printed matter or a photograph, for example, a photosensor array configured by arranging photoelectric conversion elements (photosensors) such as a CCD (Charge Coupled Device) in a line shape or a matrix shape. The one with is known. In such an image reading device, by irradiating the subject placed on the detection surface on the photosensor array with light, reading the reflected light by each photosensor, and converting it into an electrical signal, A subject image can be read.

  Here, as a technique for reading (capturing) a subject image as a color image, in general, a photosensor array including a monochrome photosensor that detects only light and dark components (lightness gradation) of the subject image, and the photosensor array A light source capable of emitting light of the three primary colors of red (R), green (G), and blue (B) disposed on the back side (opposite side of the detection surface) of The monochrome photosensor array, the detection surface side of the photosensor array, the red, green, and blue color filters arranged corresponding to each photosensor, and the backside of the photosensor array, etc. A configuration including a light source capable of emitting monochromatic (for example, white) light is known.

  In the former configuration, the light sources are sequentially switched in red, green, and blue colors to emit light, and the reflected red light, green light, and blue light emitted to the subject are each monochrome type that constitutes the photosensor array. Based on the signal level obtained when entering the photosensor, the image data for each color of red, green, and blue is read in time series, and the image data is combined to generate a color image of the subject. . An image reading apparatus having such a configuration is described in, for example, Patent Document 1 and the like.

  In the latter configuration, the monochromatic light (white light) reflected from the light source to the subject passes through the red, green, and blue color filters disposed on the photosensor array, and each monochrome type is reflected. Based on the signal level obtained when entering the photo sensor, the image data for each color of red, green, and blue is read simultaneously and synthesized to generate a color image of the subject. . An image reading apparatus having such a configuration is described in, for example, Patent Document 2.

Japanese Patent Laid-Open No. 10-32681 (2nd page, FIG. 5) JP 2000-324298 A (page 3 to page 4, FIG. 2)

However, the conventional image reading apparatus as described above has the following problems.
That is, in the method (the former configuration) in which the light source is sequentially switched between red, green, and blue to emit light, and the reflected light of each color is detected in time series by a monochrome photosensor, the light emission control of the light source is performed. In addition to being complicated, there is a problem that reading time becomes long.

  In addition, in a method of detecting reflected light of monochromatic light emitted from a light source through a color filter (the latter configuration), it is necessary to provide a filter for each color of red, green, and blue corresponding to each photosensor. In addition, since the subject image is read with a set of three photosensors (one reading pixel) corresponding to each color of red, green, and blue, in order to read the read image as a high-definition color image There has been a problem that the photosensor array has to be miniaturized to make the photosensor array highly precise.

  Therefore, in view of the above problems, the present invention provides a photosensor that can easily read a subject image as a color image with a configuration in which light emission control of a light source is simple and a high-definition read image is possible. An object of the present invention is to provide an image reading apparatus to which the photosensor is applied.

  According to the first aspect of the present invention, a light sensor provided on a transparent insulating substrate detects light of a plurality of color components corresponding to a color image of a subject, converts the light into an electric signal, and outputs the signal. The light receiving means includes a plurality of light receiving portions having light receiving sensitivities corresponding to each of the light of the plurality of color components, and the plurality of light receiving portions have a thin film transistor structure, and on the insulating substrate, It is characterized in that it is formed by laminating so that planar spreads overlap each other.

According to a second aspect of the present invention, in the photosensor according to the first aspect, in the plurality of light receiving portions, a light receiving sensitivity to the light of each color component is set according to a film thickness of a semiconductor layer constituting a channel region of the thin film transistor. It is characterized by.
According to a third aspect of the present invention, in the photosensor according to the second aspect, the semiconductor layer constituting the channel region of the thin film transistor is formed of an amorphous silicon film.

  According to a fourth aspect of the present invention, in the photosensor according to the first aspect, at least the plurality of light receiving units are set to have a high light receiving sensitivity with respect to light of a color component having a first wavelength band in the light of each color component. The first light-receiving unit, the second light-receiving unit set with high light-receiving sensitivity with respect to light of the color component having the second wavelength band, and the light-receiving sensitivity with respect to light of color component having the third wavelength band are high. It is characterized by having a configuration in which the set third light receiving section is laminated.

  According to a fifth aspect of the present invention, in the photosensor according to the fourth aspect, each of the first and second light receiving portions includes a drain electrode and a source electrode formed with the semiconductor layer sandwiched therebetween, and the semiconductor layer. An upper gate electrode made of a transparent electrode material formed through an insulating film having transparency above, and a transparent electrode formed through a transparent insulating film below the channel region A third gate light-receiving portion, a drain electrode and a source electrode formed on both sides of the semiconductor layer; and a third gate electrode formed above the semiconductor layer. An upper gate electrode made of a transparent electrode material formed through a transparent insulating film and a transparent insulating film formed under the channel region. Characterized in that it has a lower gate electrode made of the electrode material having a light shielding property, a double gate thin film transistor structure having.

According to a sixth aspect of the present invention, in the photosensor according to the fifth aspect, each of the drain electrode and the source electrode constituting the first to third light receiving portions is made of an amorphous silicon film, It is formed integrally.
According to a seventh aspect of the present invention, in the photosensor according to any one of the fourth to sixth aspects, a center wavelength of the first wavelength band is 450 nm, and a center wavelength of the second wavelength band is 550 nm. The center wavelength of the third wavelength band is 600 nm.

According to an eighth aspect of the present invention, in the photosensor according to the seventh aspect, in the photosensor, a film thickness of the semiconductor layer constituting the first light receiving portion is set to 50 nm, and the second light receiving portion The thickness of the semiconductor layer constituting the channel region is set to 150 nm, the thickness of the semiconductor layer constituting the channel region of the third light receiving portion is set to 300 nm, and the light is transmitted from the first to the first The semiconductor layers constituting the three light receiving portions are sequentially transmitted.
According to a ninth aspect of the present invention, in the photosensor according to any one of the fourth to seventh aspects, the photosensor includes at least the first and second light receiving units, and the second and third. An adjustment layer made of an amorphous silicon film is provided between the light receiving portions.

According to a tenth aspect of the present invention, in the photosensor according to the ninth aspect, the photosensor includes a total film thickness of the amorphous silicon film through which the light from the subject is transmitted, in the first light receiving unit. Including the semiconductor layer constituting one light receiving portion, the thickness is set to 50 nm, and in the second light receiving portion, the semiconductor layer, the adjustment layer, and the second light receiving portion constituting the first light receiving portion. Including the semiconductor layer that constitutes the portion, and is set to 200 nm, and the third light receiving portion constitutes the semiconductor layer, the adjustment layer, and the second light receiving portion that constitute the first light receiving portion. Including the semiconductor layer and the semiconductor layer constituting the third light receiving portion, the thickness is set to 500 nm.
The invention described in claim 11 is the photosensor according to claim 9 or 10, wherein the thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be the same. To do.

  The invention according to claim 12 includes a photosensor array in which a plurality of photosensors are arranged, and includes a plurality of color components corresponding to a color image of the subject out of light reflected by irradiating the desired subject with light. In the image reading device that detects light by the photosensor and reads it as an electrical signal corresponding to the color image, the photosensor has a plurality of light receiving sensitivities corresponding to each of the light of the plurality of color components. The light receiving portion is provided, and the plurality of light receiving portions have a thin film transistor structure and are stacked and formed on the insulating substrate so that the planar spreads overlap each other.

  According to a thirteenth aspect of the present invention, in the image reading device according to the twelfth aspect, in the plurality of light receiving portions, a semiconductor layer constituting a channel region of the thin film transistor is formed of an amorphous silicon film, and the film thickness of the amorphous silicon film Thus, the light receiving sensitivity for the light of each color component is set.

  According to a fourteenth aspect of the present invention, in the image reading device according to the twelfth aspect, the image reading device simultaneously resets at least the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array. Upper gate driving means for outputting a control signal for setting the state, and a lower gate for outputting a control signal for simultaneously setting the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array to a reading state Drive means, precharge means for outputting a control signal for simultaneously setting the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array to a precharge state, and arranged in the photosensor array The light of each color component corresponding to the color image of the subject is detected from the plurality of light receiving portions of the plurality of photosensors. The electrical signals generated Te and characterized by comprising a reading means for reading separately the each color component.

  According to a fifteenth aspect of the present invention, in the image reading device according to the twelfth aspect, the plurality of light receiving units are set to have a high light receiving sensitivity with respect to light of a color component having a first wavelength band in the light of each color component. The first light receiving unit, the second light receiving unit set to have a high light receiving sensitivity with respect to the light of the color component having the second wavelength band, and the light receiving sensitivity with respect to the light of the color component having the third wavelength band. It is characterized by having a configuration in which a third light receiving portion set high is stacked.

  According to a sixteenth aspect of the present invention, in the image reading device according to the fifteenth aspect, each of the first to third light receiving portions includes at least a drain electrode and a source electrode formed with the semiconductor layer interposed therebetween, and A double gate type having an upper gate electrode formed through a transmissive insulating film above a semiconductor layer and a lower gate electrode formed through a transmissive insulating film below the channel region It has a thin film transistor structure.

The invention according to claim 17 is the image reading apparatus according to claim 15 or 16, wherein a center wavelength of the first wavelength band is 450 nm, and a center wavelength of the second wavelength band is 550 nm, The center wavelength of the third wavelength band is 600 nm.
The invention according to claim 18 is the image reading device according to any one of claims 15 to 17, wherein the photosensor has a total film thickness of the amorphous silicon film through which the light reflected by the subject is transmitted. The first light receiving part is set to 50 nm including the semiconductor layer constituting the first light receiving part, and the second light receiving part constitutes the first and second light receiving parts. It is set to be 200 nm including the semiconductor layer, and is set to be 500 nm including the semiconductor layers constituting the first to third light receiving portions in the third light receiving portion. Features.

According to a nineteenth aspect of the present invention, in the image reading device according to the eighteenth aspect, the film thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be different from each other. To do.
According to a twentieth aspect of the present invention, in the image reading device according to the eighteenth aspect, the film thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be the same. .

  The photosensor and the image reading apparatus according to the present invention have light of color components (for example, red, green, and blue color components) corresponding to the color image of the subject among the light reflected by irradiating the desired subject with light. Is detected by a plurality of photosensors arranged in a photosensor array, and a color image of a subject is generated based on the detection signal (reading data signal), and each photosensor has a thin film transistor structure. The light receiving units (for example, first to third light receiving units) are stacked on each other, and each light receiving unit is configured to absorb and detect light of color components having different wavelength bands. ing.

  Here, in the plurality of light receiving portions, the semiconductor layer constituting the channel region is formed of an amorphous silicon film, and by appropriately setting the film thickness of the amorphous silicon film, the plurality of light receiving portions can detect light in the wavelength bands corresponding to the color components. Therefore, it is possible to realize a spectral sensitivity characteristic equivalent to that when a color filter is applied.

  In particular, by setting the total thickness of the amorphous silicon film through which the light reflected by the subject is transmitted to be 50 nm in the first light receiving portion, the blue light having a wavelength band with a center wavelength of 450 nm in the first light receiving portion. The component light can be absorbed well, and by setting the second light receiving unit to be 200 nm, the second light receiving unit can absorb green component light having a central wavelength band of 550 nm. By setting the third light receiving portion to be 500 nm, the third light receiving portion can absorb the red component light having the wavelength band of the center wavelength of 600 nm satisfactorily.

  In addition, according to the present invention, a reading pixel region (pixel area) for one pixel is applied by applying an element structure in which three layers of light receiving portions using the amorphous silicon film set to the above thickness as a semiconductor layer are stacked. ), The blue component, green component, and red component contained in the incident light (reflected light from the subject) can be detected simultaneously, so that the subject image can be read as a high-definition color image. It is not necessary to control the emission color of the light source as applied to the prior art, and without using a color filter, a detection signal corresponding to the color of the subject is read in a short time, and an appropriate color image is quickly obtained. Can be generated.

  In addition, by applying a double gate type photosensor to each light receiving part, it is possible to provide a selection function and a photo sensing function with a single element structure, so that each photosensor is in a selected state like a well-known CCD. Therefore, it is not necessary to provide a selection transistor for each read pixel individually, and it is possible to easily reduce the size of the system and increase the density of the read pixels.

Hereinafter, a photosensor according to the present invention and an image reading apparatus to which the photosensor is applied will be described in detail with reference to embodiments.
First, a configuration and control operation of a photo sensor that is favorable to the present invention and a photo sensor system to which the photo sensor is applied will be described.

  Here, as a photosensor applicable to the present invention, a photosensor having a so-called double gate type thin film transistor structure in which the photosensor itself has a photosense function and a select transistor function (hereinafter referred to as “double gate type”). (Referred to as “photosensor”) can be applied satisfactorily.

<Double gate type photo sensor>
FIG. 1 is a schematic sectional view showing an element structure of a double gate type photosensor applicable to the image reading apparatus according to the present invention.
As shown in FIG. 1A, a double-gate photosensor PS generally includes a semiconductor layer (channel region) such as amorphous silicon in which electron-hole pairs are generated by the incidence of excitation light (here, visible light). ) 11 and both ends of the semiconductor layer 11 through n ⁺ silicon impurity layers (ohmic contact layers) 17 and 18, respectively, and selected from chromium, chromium alloy, aluminum, aluminum alloy, etc. A drain electrode 12 (drain terminal D) and a source electrode 13 (source terminal S) which are made of a material and are opaque to visible light, a block insulating film (stopper film) 14 and an upper portion above the semiconductor layer 11 (upward in the drawing) A transparent electrode layer such as a tin oxide film or an ITO film (indium-tin oxide film) formed through the gate insulating film 15 and having transparency to visible light. A gate electrode TGx (upper gate electrode; top gate terminal TG) and a lower gate insulating film 16 below the semiconductor layer 11 (downward in the drawing) and selected from chromium, chromium alloy, aluminum, aluminum alloy, etc. A bottom gate electrode BGx (lower gate electrode; bottom gate terminal BG) made of a conductive material and opaque to visible light is configured.

  The double-gate photosensor PS having such a configuration is formed on a transparent insulating substrate SUB such as a glass substrate as shown in FIG. In addition, a protective insulating film 19 is formed on the entire surface of the insulating substrate SUB including the double-gate photosensor PS, so that electrical, physical, and chemical damage and erosion of the double-gate photosensor PS are performed. Is configured to prevent.

  Here, in the double gate type photosensor PS shown in FIG. 1A, as a basic element structure, an insulating film constituting the top gate insulating film 15, the block insulating film 14, and the bottom gate insulating film 16, The protective insulating film 19 provided on the top gate electrode TGx is made of a material having a high transmittance for visible light that excites the semiconductor layer 11, for example, silicon nitride, silicon oxide, or the like. Thus, the radiated light from the light source (not shown) provided in the lower part of the drawing is transmitted to the upper side of the figure, and reflected to the subject placed on the detection surface DTC provided on the upper surface of the protective insulating film 19, It has a structure for detecting only light incident on the double gate type photosensor PS (specifically, the semiconductor layer 11) from the upper side of the drawing.

  Such a double-gate photosensor PS is generally represented by an equivalent circuit as shown in FIG. Here, TG is a top gate terminal electrically connected to the top gate electrode TGx, BG is a bottom gate terminal electrically connected to the bottom gate electrode BGx, and D is a drain electrically connected to the drain electrode 12. A terminal S is a source terminal electrically connected to the source electrode 13.

<Photo sensor system>
Next, a photo sensor system including a photo sensor array configured by two-dimensionally arranging the above-described double gate type photo sensors on an insulating substrate will be described.
FIG. 2 is a schematic configuration diagram of a photosensor system to which a double gate type photosensor is applied. Here, a photosensor array configured by two-dimensionally arranging a plurality of double-gate photosensors will be described and described. However, a plurality of double-gate photosensors are, for example, linearly (X direction) 1 A line sensor array may be configured by dimensionally arranging, and the line sensor array may be moved in a direction perpendicular to the extending direction (Y direction orthogonal to the X direction) to scan (scan) a two-dimensional region. .

  As shown in FIG. 2, the photosensor system is roughly divided into a photosensor array in which a plurality of double-gate photosensors PS are arranged in a matrix of, for example, n rows × m columns (n and m are arbitrary natural numbers). 100, a top gate line Lt extending by connecting the top gate terminal TG (top gate electrode TGx) of each double-gate photosensor PS in the row direction, and a bottom gate terminal BG (bottom) of each double-gate photosensor PS The bottom gate line Lb extending by connecting the gate electrode BGx) in the row direction, and the drain line (data line) extending by connecting the drain terminal D (drain electrode 12) of each double-gate photosensor PS in the column direction A source line (common line) for commonly connecting Ld and the source terminal S (source electrode 13) to the ground potential s, a top gate driver (upper gate driving means) 110 connected to the top gate line Lt, a bottom gate driver (lower gate driving means) 120 connected to the bottom gate line Lb, and a drain line Ld And a drain driver (precharge means, read means) 130.

  In FIG. 2, the top gate control signal is a signal φT1, φT2,... Selectively output to the top gate line Lt as either a reset voltage (reset pulse) or a carrier storage voltage in the top gate driver 110. φTi,..., φTn, and the bottom gate control signal is a signal φB1 selectively output to the bottom gate line Lb as either a read voltage or a non-read voltage in the bottom gate driver 120. , ΦB2,... ΦBi,... ΦBn are precharge signals for controlling the timing at which the drain driver 130 applies the precharge voltage Vpg to the drain line Ld. Details will be described in the drive control method.

(Drive control method)
Next, a driving control method of the above-described photosensor array system (double gate type photosensor) will be briefly described with reference to the drawings.
FIG. 3 is a timing chart showing an example of a drive control method of a photo sensor system to which a double gate type photo sensor is applied.

For example, as shown in FIG. 3, the drive control method for the sensor array 100 described above includes a reset period Trst, a charge accumulation period Ta, a precharge period Tprch, and a readout period Tread in a predetermined processing operation period (one processing cycle). This is realized by setting.
First, in the reset period Trst, the top gate driver 110 passes the top gate line Lt to the top gate terminal TG of the i-th row (i is an arbitrary integer of 1 ≦ i ≦ n) double gate photosensor PS. Applying a reset pulse (for example, high level of top gate voltage Vtg = + 15V; reset control signal) φTi to reset carriers (here, holes) accumulated in the semiconductor layer 11 (initializing operation) ).

  Next, in the charge accumulation period Ta, the top gate driver 110 applies a low level (for example, top gate voltage Vtg = −15V) bias voltage φTi to the top gate terminal TG, thereby terminating the reset operation. The accumulation operation (carrier accumulation operation) is started.

  Here, in the charge accumulation period Ta, for example, a light source (not shown) provided on the back side (lower side in FIG. 1) of the transparent insulating substrate SUB on which the double-gate photosensor PS shown in FIG. 1 is formed. ), The reflected light of the light irradiated to the subject placed on the detection surface DTC on the upper surface of the sensor array 100 passes through the top gate electrode TGx made of a transparent electrode layer and enters the semiconductor layer 11. Thus, electron-hole pairs are generated in the incident effective region (carrier generation region) of the semiconductor layer 11 according to the amount of light incident on the semiconductor layer 11 during the charge accumulation period Ta, and the semiconductor layer 11 and the block insulating film 14 Holes are accumulated in the vicinity of the interface (around the channel region).

  In the precharge period Tprch, the drain driver 130 precharges the drain terminal D via the drain line Ld based on the precharge signal φpg supplied as a drain control signal in parallel with the charge accumulation period Ta. A charge pulse (for example, drain voltage VD (= precharge voltage Vpg) = + 5 V; precharge control signal) is applied, and a precharge operation for holding the charge in the drain electrode 12 is executed.

  Next, in the read period Tread, after the precharge period Tprch has elapsed, a read pulse (for example, a bottom gate voltage (= read pulse voltage)) is applied to the bottom gate terminal BG by the bottom gate driver 120 via the bottom gate line Lb. By applying Vbg = + 10V high level; read control signal) φBi, a drain voltage VD (= data voltage Vrd; electrical signal) corresponding to carriers (holes) accumulated in the channel region during the charge accumulation period Ta is applied. The read operation is performed by the drain driver 130 via the drain line Ld.

  Here, the change tendency of the drain voltage VD (data voltage Vrd) during the application period (readout period) of the read pulse φBi indicates that the voltage is steep when there are many carriers accumulated in the charge accumulation period Ta (bright state). On the other hand, when the accumulated carriers are small (dark state), the data tends to decrease gradually. For example, the data voltage Vrd after the elapse of a predetermined time from the start of the read period Tread is detected. Thus, it is possible to detect the amount of light incident on the double gate type photosensor PS, that is, brightness data (brightness information) corresponding to the brightness pattern of the subject.

  Then, a series of brightness data detection operations for such a specific row (i-th row) is regarded as one cycle, and each row (i = 1, 2,... N) of the sensor array 100 described above is equivalent. By repeating the operation process, the sensor array 100 to which the double-gate photosensor PS is applied can be operated as a photosensor system that reads a two-dimensional image of a subject as lightness data.

Next, the photosensor according to the present invention will be specifically described. Here, an embodiment of a photosensor to which the element structure of the double gate photosensor described above is applied will be described.
<First Embodiment of Photosensor>
FIG. 4 is a schematic cross-sectional view showing the first embodiment of the element structure of the photosensor according to the present invention, and FIG. 5 is a concept showing the light absorption state of each light receiving unit in the photosensor according to this embodiment. FIG. Here, for the sake of illustration, the element structure of the double-gate photosensor shown in FIG. 1 is simplified and corresponding components will be described with the same or equivalent reference numerals. In FIG. 5, hatching is omitted for convenience of illustration.

  As shown in FIG. 4, the photosensor according to the present embodiment has a first double-gate photosensor (first photosensor) serving as the uppermost light receiving portion on one surface side of a transparent insulating substrate SUB such as a glass substrate. (Light receiving portion) PSA, second double gate photosensor (second light receiving portion) PSB serving as the light receiving portion of the intermediate layer, and third double gate photosensor (third light receiving portion) serving as the lowermost light receiving portion. Light receiving part) PSC. Although not shown, white light is emitted to the subject placed on the detection surface DTC provided on the upper surface of the first double-gate photosensor PSA on the back side (lower side of the drawing) of the insulating substrate SUB. It may have a configuration in which a light source (surface light source) for irradiating is disposed.

  The first double-gate photosensor PSA is roughly composed of a drain electrode 12a and a source electrode 13a connected to both ends of a semiconductor layer 11a made of amorphous silicon, and an upper gate insulating film 15a above the semiconductor layer 11a. On the top gate electrode TGa formed of the formed transparent electrode layer, the bottom gate electrode BGa formed below the semiconductor layer 11a via the lower gate insulating film 16a, and the upper gate insulating film 15a including the top gate electrode TGa And a protective insulating film 19a having a coating formed thereon. The impurity layers (ohmic contact layers) 17 and 18 and the block insulating film (stopper film) 14 shown in FIG.

  Here, similarly to the element structure shown in FIG. 1, the upper gate insulating film 15a, the lower gate insulating film 16a, and the protective insulating film 19a are made of an insulating film having a high transmittance such as silicon nitride or silicon oxide. Unlike the element structure shown in FIG. 1, at least the bottom gate electrode BGa is composed of an electrode layer (transparent electrode layer) having a high transmittance such as a tin oxide film or an ITO film.

  Thereby, light incident from above the first double-gate photosensor PSA enters the semiconductor layer 11a via the protective insulating film 19a, the top gate electrode TGa, and the upper gate insulating film 15a, and further, the semiconductor The light passes through the layer 11a, passes through the lower gate insulating film 16a and the bottom gate electrode BGa, and enters the second double-gate photosensor PSB formed in the lower layer.

  The second double-gate photosensor PSB is roughly similar to the first double-gate photosensor PSA, and includes a semiconductor layer 11b made of amorphous silicon, a drain electrode 12b and a source electrode 13b, and an upper gate insulation. Interlayer insulating film 19b coated on film 15b, top gate electrode TGb made of a transparent electrode layer, lower gate insulating film 16b, bottom gate electrode BGb, and upper gate insulating film 15b including top gate electrode TGb And is configured.

  Here, the upper gate insulating film 15b, the lower gate insulating film 16b, and the interlayer insulating film 19b are made of an insulating film having a high transmittance such as silicon nitride or silicon oxide, and at least the bottom gate electrode BGb is also a tin oxide film. And a transparent electrode layer having a high transmittance such as an ITO film.

  As a result, light that passes through the first double-gate photosensor PSA and enters from above the second double-gate photosensor PSB passes through the interlayer insulating film 19b, the top gate electrode TGb, and the upper gate insulating film 15b. A third double-gate photosensor PSC that is transmitted through and incident on the semiconductor layer 11b and further transmitted through the semiconductor layer 11b and formed in the lower layer through the lower gate insulating film 16b and the bottom gate electrode BGb. Is incident on.

  The third double-gate photosensor PSC has a drain electrode 12c and a source electrode 13c connected to both ends of a semiconductor layer 11c made of amorphous silicon, as in the element structure shown in FIG. A top gate electrode TGc made of a transparent electrode layer formed above the semiconductor layer 11c via an upper gate insulating film 15c, and an opaque bottom gate electrode formed below the semiconductor layer 11c via a lower gate insulating film 16c. The interlayer insulating film 19c is formed on the upper gate insulating film 15c including the BGc and the top gate electrode TGc.

  Here, similarly to the element structure shown in FIG. 1, the upper gate insulating film 15c, the lower gate insulating film 16c, and the interlayer insulating film 19c are composed of an insulating film having a high transmittance such as silicon nitride or silicon oxide. The bottom gate electrode BGc is composed of an opaque electrode layer selected from chromium, a chromium alloy, aluminum, an aluminum alloy, or the like.

  As a result, the light that passes through the first double gate photosensor PSA and the second double gate photosensor PSB and enters from above the third double gate photosensor PSC is transmitted through the interlayer insulating film 19c and the top. The light passes through the gate electrode TGc and the upper gate insulating film 15c and enters the semiconductor layer 11c. The light transmitted through the semiconductor layer 11c is blocked by the opaque bottom gate electrode BGb through the lower gate insulating film 16c, and is prevented from entering the insulating substrate SUB formed in the lower layer.

Furthermore, in the photosensor according to the present embodiment, the film thickness of the amorphous silicon film constituting the semiconductor layer of the double-gate photosensor of each light receiving unit is set as follows, for example.
(1) Semiconductor layer 11a of first double-gate photosensor PSA: film thickness 50 nm
(2) Semiconductor layer 11b of second double-gate photosensor PSB: film thickness 150 nm
(3) Semiconductor layer 11c of third double gate type photosensor PSC: film thickness of 300 nm

  The light absorption characteristics of the photosensor (each double-gate photosensor) having such an element structure are as follows. First, in the first double-gate photosensor PSA of the uppermost layer, the amorphous silicon film constituting the semiconductor layer 11a By setting the thickness to 50 nm, as indicated by an arrow LYa in FIG. 5, among the light incident on the semiconductor layer 11 a (amorphous silicon film), a wavelength of 450 nm and its nearby wavelength band (first wavelength band) Only the blue light having s is absorbed by the semiconductor layer (channel region) 11a.

  In the double-gate photosensor PSB of the intermediate layer, by setting the thickness of the amorphous silicon film constituting the semiconductor layer 11b to 150 nm, the thickness of the semiconductor layer 11b (150 nm) is substantially reduced. An amorphous silicon film having a total film thickness of 200 nm including the film thickness (50 nm) of the layer 11a is formed. Of the light transmitted through the semiconductor layer 11a of the first double-gate photosensor PSA, FIG. In the middle, as indicated by an arrow LYb, only green light having a wavelength of 550 nm and a wavelength region near it (second wavelength band) is absorbed by the semiconductor layer (channel region) 11b.

  Furthermore, in the double-gate photosensor PSC at the lowest layer, by setting the film thickness of the amorphous silicon film constituting the semiconductor layer 11c to 300 nm, the semiconductor layer 11c is substantially reduced in thickness (300 nm). An amorphous silicon film having a total film thickness of 500 nm is formed by adding the film thickness of the layer 11a (50 nm) and the film thickness of the semiconductor layer 11b (150 nm), and the semiconductor layer of the first double-gate photosensor PSA is formed. 11a and red light having a wavelength of 550 nm and its nearby wavelength band (third wavelength band) as shown by an arrow LYc in FIG. 5 among the light transmitted through the semiconductor layer 11b of the second double-gate photosensor PSB. Only light is absorbed by the semiconductor layer (channel region) 11c.

Here, in the present embodiment, the double gate type photosensors PSA, PSB, and PSC of each light receiving unit each have a configuration as an individual double gate type photosensor, similarly to the element structure shown in FIG. However, by executing the drive control method shown in FIG. 3 simultaneously (in parallel) on each of the double gate photosensors PSA, PSB, and PSC, the semiconductor layers 11a, 11b, and 11c Light having specific wavelengths (color components) absorbed individually can be detected simultaneously.
In addition, it is also possible to detect only light of an arbitrary wavelength (color component) by driving or controlling the double gate type photosensors PSA, PSB, and PSC of each light receiving unit individually or independently.

Here, the light absorption characteristics of the amorphous silicon film according to the present invention will be described in detail.
FIG. 6 is a diagram for explaining the relationship between the film thickness of the amorphous silicon film applied to the photosensor according to this embodiment and the absorption wavelength. Here, FIG. 6A is a diagram showing general spectral sensitivity characteristics (spectral characteristics) in red, green, and blue colors in the NTSC video signal standard, and FIG. It is a figure which shows the absorption wavelength characteristic (light absorption characteristic) with respect to the film thickness of the amorphous silicon film (semiconductor layer) applied to the photosensor which concerns on embodiment. In FIG. 6B, in order to clarify the difference from the spectral sensitivity characteristic shown in FIG. 6A, a characteristic curve is superimposed on the same graph.

  As shown in FIG. 6A, the general spectral sensitivity characteristics (color matching functions) of red, green, and blue in the NTSC video signal standard are such that blue light has a wavelength of 450 nm and a wavelength region in the vicinity thereof. It has a relatively steep peak, green light has a relatively steep peak at a wavelength of 550 nm and its nearby wavelength region, and red light has a relatively steep peak at a wavelength of 600 nm and its nearby wavelength region. .

  On the other hand, as shown in this embodiment, the absorption wavelength characteristic when the total film thickness of the amorphous silicon film is set is as shown in FIG. 6B when the total film thickness is 50 nm. When the total film thickness is 200 nm, the total film thickness is approximately 540 to 560 nm. When the total film thickness is 500 nm, the wavelength is approximately 590. It has a gentle peak at ˜610 nm.

That is, as shown in FIG. 6B, it is found that an absorption wavelength characteristic having a peak substantially equal to the peak in the NTSC RGB spectral sensitivity characteristic can be obtained by appropriately setting the film thickness of the amorphous silicon film. did.
Therefore, by appropriately setting the substantial film thickness (that is, the total film thickness) of the semiconductor layers constituting each light receiving unit (double gate type photosensor) corresponding to each color of red, green, and blue, red, Spectral sensitivity characteristics similar to the case where a color filter that absorbs only light of wavelengths of green and blue are applied can be realized.

When the absorption wavelength characteristic in such an amorphous silicon film is further verified based on an optical theory, first, in general, light absorption in a transparent film having a specific film quality is expressed by the following differential equation (11). Can do.
dI (λ) / dx = −α (λ) · I (λ) (11)
Here, I (λ) is the light intensity, x is the depth (corresponding to the film thickness) from the surface of the transparent film, and α is the light absorption coefficient in the transparent film.

When the light intensity I (λ) on the surface (x = 0) of the transparent film is I0, the above equation (11) can be expressed by the following equation (12).
I = I0 · exp {−α (λ) · x} (12)
Substituting this result into equation (11) again yields the following equation (13).
dI (λ) / dx = −I0 · α (λ) · exp {−α (λ) · x} (13)

From the above equation (13), the absorption spectrum at the depth x is equivalent to the case where the color filter having the spectral spectrum characteristic of the following equation (14) is applied.
S (λ) = α (λ) · exp {−α (λ) · x} (14)
If S (λ) in the above equation (14) approximates the color matching function of the RGB color system (spectral sensitivity characteristics shown in FIG. 6A), the transparent film (that is, the semiconductor layer) is formed. (Amorphous silicon film) itself can be applied as a structure having a function equivalent to an RGB color filter.

Therefore, the following equation (15) can be obtained by differentiating the above equation (14) by λ in order to verify the wavelength dependence of S (λ).
dS (λ) / dλ = {1−α (λ) · x} · dα / dλ · exp {−α (λ) · x} (15)
Here, if α is monotonic (dα / dλ is positive or negative and does not become 0), a maximum peak is shown at λ satisfying the following expression (16).
1-α (λ) · x = 0 (16)

  On the other hand, the peak wavelength of the color matching function of the RGB color system is approximately 450 nm in the blue system (B), approximately 550 nm in the green system (G), and approximately 600 nm in the red system (R), as described above. If light absorption at a depth x such that the above equation (16) holds is detected at these peak wavelengths, it can be regarded approximately as light components of blue, green, and red colors.

  Here, the light absorption spectrum of the amorphous silicon film applied to the light receiving portion of the photosensor according to the present embodiment (semiconductor layer of the double gate type photosensor) generally has a strong wavelength dependency and is in the visible light region. Since it is known that a monotonous change is exhibited, the above-described technical idea can be favorably applied.

Next, in the case where an amorphous silicon film is applied as the transparent film, a film thickness suitable for detecting light having the wavelength components of blue, green, and red described above is derived.
FIG. 7 is a characteristic diagram showing the relationship between the wavelength of light and the light absorption coefficient in an amorphous silicon film.

According to the characteristic diagram shown in FIG. 7, the light absorption coefficient α of the wavelengths of blue, green, and red in the amorphous silicon film is approximately α (450 nm) = 2.0E + 7 m ^{−1 in} the case of blue (in the figure, α (B) point), in the case of green, approximately α (550 nm) = 5.0E + 6 m ⁻¹ (in the figure, α (g) point), and in the case of red, generally α (600 nm) = 2.0 E + 6 m ^{Since it is} about ⁻¹ (α (r) point in the figure), when an optimum film thickness (depth x) is obtained based on the above equation (16), it is about 50 nm in the case of blue. In the case of green, the numerical value is approximately 200 nm, and in the case of red, a numerical value of approximately 500 nm is calculated.
That is, by setting the thickness of a single amorphous silicon film or the total thickness of a plurality of amorphous silicon films to 50 nm, 200 nm, and 500 nm, respectively, specific color components of blue, green, and red are set. Can absorb only light having

  Therefore, according to the photosensor according to the present embodiment, as described above, paying attention to the fact that the amorphous silicon film has different light absorption characteristics depending on the film thickness (absorption wavelength depends on the film thickness), the double gate serving as the light receiving unit In an element structure in which stacked photosensors are stacked so as to overlap each other, the amorphous silicon film constituting the semiconductor layer of each double-gate photosensor is set to a film thickness corresponding to each color of blue, green, and red By doing so, it is possible to realize a spectral sensitivity characteristic equivalent to that when a color filter is applied.

  In particular, by applying an element structure in which three layers of double gate type photosensors using an amorphous silicon film having a film thickness as shown in (1) to (3) described above as a semiconductor layer are applied, one pixel is obtained. The blue, green, and red components contained in the incident light (reflected light from the subject) can be detected simultaneously in a single read pixel area (pixel area), so that the element structure has a high density. The subject image can be read as a high-definition color image, and it is not necessary to control the light emission color of the light source as shown in the prior art, and it corresponds to the subject color without using a color filter The detected signal can be read in a short time, and an appropriate color image can be quickly generated.

  Further, in the well-known CCD, since it is necessary to provide a selection transistor for making each photosensor in a selected state for each photosensor, if the number of read pixels is increased in order to improve reading accuracy, In contrast to the problem that the system itself is increased in size, a single element structure can be obtained by applying a double gate type photosensor to each light receiving portion constituting the photosensor as in this embodiment. Thus, since the selection function and the photo sensing function can be provided, the system can be further miniaturized and the density of read pixels can be increased.

  As shown in FIG. 5B, in the configuration in which the film thickness of the amorphous silicon film is appropriately set, although the absorption wavelength peaks substantially coincide with the spectral sensitivity characteristics of the NTSC system, The curve has a relatively gentle spread in the wavelength range centered on the peak. In order to approximate such a characteristic curve with an ideal value (NTSC spectral sensitivity characteristic), for example, a method for mathematically correcting the characteristic curve (for example, matrix correction) or an optical element such as a filter is provided. Then, a method of correcting by an element structure, a method of applying a light source (backlight) that emits light having spectral characteristics for correcting distortion of a characteristic curve, etc., may be applied alone or in combination as appropriate. it can.

<Second Embodiment of Photosensor>
Next, a second embodiment of the photosensor according to the present invention will be described with reference to the drawings.
FIG. 8 is a schematic sectional view showing a second embodiment of the element structure of the photosensor according to the present invention. Here, about the structure equivalent to 1st Embodiment mentioned above, the same or equivalent code | symbol is attached | subjected and the description is simplified.

  As shown in FIG. 8, the photosensor according to the present embodiment has a first double-gate photosensor (first light receiving portion) PSD serving as the uppermost light receiving portion on one surface side of the insulating substrate SUB. A second double-gate photosensor (second light-receiving unit) PSE serving as a light-receiving unit in the intermediate layer; a third double-gate photosensor (third light-receiving unit) PSF serving as the light-receiving unit in the lowermost layer; Has a configuration in which the layers are stacked. Although not shown, the present embodiment also has a configuration in which a light source (surface light source) that irradiates a subject with white light is disposed on the back side (lower side of the drawing) of the insulating substrate SUB. There may be.

  In general, the first double-gate photosensor PSD includes a drain electrode 12d and a source electrode 13d integrally formed on both ends of an amorphous silicon semiconductor layer 11d, and an upper gate insulating film 15d above the semiconductor layer 11d. A top gate electrode TGd made of a transparent electrode layer formed via the upper gate electrode TGd, and a protective insulating film 19d formed on the upper gate insulating film 15d including the top gate electrode TGd.

  Here, the semiconductor layer 11d, the drain electrode 12d, and the source electrode 13d are conductive by injecting impurities only into the formation region of the drain electrode 12d and the source electrode 13d into the integrally formed amorphous silicon film. The semiconductor layer 11d is formed by retaining the semiconductor characteristics so that impurities are not implanted into the formation region of the semiconductor layer 11d. Similarly to the element structure shown in FIG. 1, the upper gate insulating film 15d and the protective insulating film 19d are made of an insulating film having a high transmittance.

The second double-gate photosensor PSE is similar to the first double-gate photosensor PSD described above, generally, the semiconductor layer 11e, the drain electrode 12e, and the source electrode 13e that are integrally formed of amorphous silicon. And an upper gate insulating film 15e formed above the semiconductor layer 11e.
Here, the upper gate insulating film 15e is composed of an insulating film having a high transmittance, and also functions as an interlayer insulating film with the first double-gate photosensor PSD described above.

The third double-gate photosensor PSF is roughly similar to the first double-gate photosensor PSD, and includes a semiconductor layer 11f, a drain electrode 12f, and a source electrode 13f that are integrally formed of amorphous silicon. And an upper gate insulating film 15f formed above the semiconductor layer 11f, and an opaque bottom gate electrode BGf formed below the semiconductor layer 11f via the lower gate insulating film 16f. Yes.
Here, the upper gate insulating film 15f and the lower gate insulating film 16f are made of an insulating film having a high transmittance, and also have a function as an interlayer insulating film for the second double-gate photosensor PSE described above.

  Furthermore, in the photosensor according to the present embodiment, the semiconductor layer (amorphous silicon film) of the first double-gate photosensor PSD, as in (1) to (3) described in the first embodiment. The film thickness of 11d is set to 50 nm, the film thickness of the semiconductor layer 11e of the second double-gate photosensor PSE is set to 150 nm, and the film thickness of the semiconductor layer 11f of the third double-gate photosensor PSF is 300 nm. Is set to

  That is, in the photosensor according to the present embodiment, the semiconductor layers 11d, 11e, and 11f made of amorphous silicon films having different film thicknesses are laminated through only the interlayer insulating films 15e and 15f, and further, For the three semiconductor layers 11d, 11e, and 11f, a single top gate electrode TGd is provided on the uppermost portion (on the upper gate insulating film 15d) and a single upper gate electrode TGd is provided on the lowermost portion (below the lower gate insulating film 16f). The structure has a bottom gate electrode.

  Thereby, light incident from above the first double-gate photosensor PSD enters the semiconductor layer 11d via the protective insulating film 19d, the top gate electrode TGd, and the upper gate insulating film 15d, and further, the semiconductor The light passes through the layer 11d and enters the second double-gate photosensor PSE formed in the lower layer.

  In addition, light incident from above the second double-gate photosensor PSE via the first double-gate photosensor PSD enters the semiconductor layer 11e via the upper gate insulating film 15e. The light passes through the semiconductor layer 11e and enters the third double-gate photosensor PSF formed in the lower layer.

  In addition, light incident from above the third double-gate photosensor PSF via the first double-gate photosensor PSD and the second double-gate photosensor PSE passes through the upper gate insulating film 15f. The light enters the semiconductor layer 11f. The light transmitted through the semiconductor layer 11f is blocked by the opaque bottom gate electrode BGf through the lower gate insulating film 16f, and is prevented from entering the insulating substrate SUB formed in the lower layer.

  Also in the photosensor according to the present embodiment, the film thickness of the amorphous silicon films (semiconductor layers 11d, 11e, and 11f) constituting the double-gate photosensor of each light receiving unit, as in the first embodiment described above. Is set to 50 nm, 150 nm, and 300 nm, respectively, as shown in the above (1) to (3), and similarly to the case shown in FIG. 5, each light receiving portion (double gate type photosensor) , Each having a specific wavelength is absorbed and detected.

  Here, in the present embodiment, the double gate photosensors PSD, PSE, PSF of each light receiving unit have a configuration having a common (single) top gate electrode TGd and bottom gate electrode BGf. A specific wavelength (color component) absorbed individually in each of the semiconductor layers 11d, 11e, and 11f by executing the drive control method shown in FIG. 3 for each double-gate photosensor PSD, PSE, and PSF. Can be detected simultaneously.

  Therefore, according to the photosensor according to the present embodiment, similarly to the first embodiment described above, in the element structure in which three layers of double gate type photosensors are stacked, light absorption corresponding to each color of blue, green, and red is performed. By setting the thickness of each semiconductor layer (amorphous silicon film) to have characteristics, the device structure can be densified and the subject image can be read as a high-definition color image, and the complex light emission of the light source An appropriate color image can be quickly generated without applying control or a color filter.

  In particular, according to the present embodiment, a common (single) top gate electrode TGd and bottom gate are provided for the semiconductor layers 11d, 11e, and 11f constituting the double gate photosensors PSD, PSE, and PSF of each light receiving unit. Since the electrode BGf is provided, the device structure of the photosensor can be further reduced, and the number of top gate lines Lt and bottom gate lines Lb can be reduced. Can be simplified to improve design easiness and yield.

  In the first embodiment described above, a case will be described in which a double gate type photosensor is provided for each light receiving unit, and each double gate type photosensor has the basic structure shown in FIG. On the other hand, in the second embodiment, each light receiving portion has a semiconductor layer, a source electrode, and a drain electrode integrally formed of an amorphous silicon film, and the top gate electrode and the bottom gate electrode are connected to each light receiving portion. However, the present invention is not limited to this. In the first embodiment, the semiconductor layer, the source electrode, and the drain electrode are integrally formed of an amorphous silicon film. In the second embodiment, the semiconductor layer, the source electrode, and the drain electrode are formed by separate thin films. Form configuration may be configured to apply the (basic structure shown in FIG. 1).

<Third Embodiment of Photosensor>
Next, a third embodiment of the photosensor according to the present invention will be described with reference to the drawings.
FIG. 9 is a schematic cross-sectional view showing a third embodiment of the element structure of the photosensor according to the present invention. Here, about the structure equivalent to 1st and 2nd embodiment mentioned above, the same or equivalent code | symbol is attached | subjected and the description is simplified.

  In each of the embodiments described above, the film thickness of the semiconductor layer (amorphous silicon film) of the double-gate photosensor that constitutes each light receiving portion has light absorption characteristics corresponding to the respective color components of blue, green, and red. As described above, the case where the uppermost light receiving part is set to 50 nm, the intermediate light receiving part is set to 150 nm, and the lowermost light receiving part is set to 300 nm. In this embodiment, the film thickness of the semiconductor layer of each light receiving part is shown. Are set uniformly.

  That is, as shown in FIGS. 9A and 9B, the photosensor according to the present embodiment has a double gate type photo that constitutes each light receiving portion in the element structure shown in the first and second embodiments. The thickness of each of the semiconductor layers (amorphous silicon films) 11a to 11c and 11d to 11f of the sensors PSA to PSC and PSD to PSF is set to 50 nm, and between the light receiving portions of the uppermost layer and the intermediate layer. In addition, a first dummy layer (adjustment layer) DMA made of an amorphous silicon film having a thickness of 100 nm is provided, and a second dummy made of an amorphous silicon film having a thickness of 250 nm is provided between the intermediate layer and the lowermost light receiving portion. A layer (adjustment layer) DMB is provided.

  As a result, light incident from above the first double-gate photosensors PSA and PSD passes through the protective insulating films 19a and 19d, the top gate electrodes TGa and TGd, and the upper gate insulating films 15a and 15d, respectively. The light enters the layers 11a and 11d. The light transmitted through the semiconductor layer 11a passes through the lower gate insulating film 16a, the bottom gate electrode BGa, the interlayer insulating film 20A, and the first dummy layer DMA to the second double-gate photosensor PSB formed in the lower layer. The incident light that has passed through the semiconductor layer 11d passes through the interlayer insulating film 20A and the first dummy layer DMA, and enters the second double-gate photosensor PSE formed in the lower layer.

  Light entering from above the second double-gate photosensor PSB via the first double-gate photosensor PSA passes through the interlayer insulating film 19b, the top gate electrode TGb, and the upper gate insulating film 15b. Light that enters the semiconductor layer 11b and enters from above the second double-gate photosensor PSE passes through the upper gate insulating film 15e and enters the semiconductor layer 11e. The light transmitted through the semiconductor layer 11b passes through the lower gate insulating film 16b, the bottom gate electrode BGb, the interlayer insulating film 20B, and the second dummy layer DMB to the third double gate type photosensor PSC formed in the lower layer. The incident light that has passed through the semiconductor layer 11e passes through the interlayer insulating film 20B and the second dummy layer DMB, and enters the third double-gate photosensor PSF formed in the lower layer.

  Further, the light incident from above the third double-gate photosensor PSC via the first double-gate photosensor PSA and the second double-gate photosensor PSB is transmitted through the interlayer insulating film 19c and the top gate electrode. Light that enters the semiconductor layer 11c through the TGc and the upper gate insulating film 15c and enters from above the third double-gate photosensor PSF passes through the upper gate insulating film 15f and enters the semiconductor layer 11f. . The light transmitted through the semiconductor layers 11c and 11f is blocked by the opaque bottom gate electrodes BGc and BGf through the lower gate insulating films 16c and 16f and is prevented from entering the insulating substrate SUB formed in the lower layer. Is done.

  Also in the photosensor according to this embodiment, as in the first and second embodiments described above, first, in the double-gate photosensors PSA and PSD of the uppermost light receiving section, a semiconductor made of an amorphous silicon film is used. Since the thickness of the layers 11a and 11d is set to 50 nm, only blue light having a wavelength near 450 nm is absorbed.

  In the double gate type photosensors PSB and PSE constituting the light receiving part of the intermediate layer, in addition to the amorphous silicon film with a film thickness of 50 nm in the light receiving part of the uppermost layer, the first dummy layer DMA with a film thickness of 100 nm, and Since the total thickness of the amorphous silicon film is set to 200 nm by the semiconductor layers 11b and 11e having a thickness of 50 nm, only the green light near the wavelength of 550 nm is absorbed by the semiconductor layers 11b and 11e.

  Further, in the double gate type photosensors PSC and PSF constituting the lowermost light receiving part, the amorphous silicon film having a film thickness of 50 nm, the first dummy layer DMA having a film thickness of 100 nm, and the light reception of the intermediate layer in the uppermost light receiving part. The total thickness of the amorphous silicon film is set to 500 nm by the second dummy layer DMB with a film thickness of 250 nm and the semiconductor layers 11c and 11f with a film thickness of 50 nm in addition to the amorphous silicon film with a film thickness of 50 nm in the portion. As a result, only red light having a wavelength in the vicinity of 600 nm is absorbed by the semiconductor layers 11c and 11f.

  That is, in the present embodiment, the film thickness of the amorphous silicon film that penetrates to the semiconductor layer of the double-gate photosensor of each light-receiving unit is the same as in the cases shown in the above (1) to (3). By setting each to 50 nm, 200 nm, and 500 nm, light having a specific wavelength is absorbed and detected by each light receiving unit (double-gate photosensor) as in the case shown in FIG.

  Therefore, according to the photosensor according to the present embodiment, the film thickness of the semiconductor layer (amorphous silicon film) constituting the double-gate photosensor of each light receiving portion can be made uniform. Variation can be suppressed, and the manufacturing process can be simplified.

  In addition, the film thickness (50 nm) of the amorphous silicon film in each light receiving portion and the film thickness (100 nm, 250 nm) of the amorphous silicon film in the first and second dummy layers are merely examples. However, the present invention is not limited to this. In short, light incident from one side of the photosensor (light reflected by the subject) is an uppermost semiconductor layer made of an amorphous silicon film with a total film thickness of 50 nm, and an intermediate layer made of an amorphous silicon film with a total film thickness of 200 nm. It is needless to say that other film thicknesses may be set as long as they are respectively absorbed by the lowermost semiconductor layer made of an amorphous silicon film having a total film thickness of 500 nm. .

  In each of the above-described embodiments, the case where a double gate type photosensor is applied as each light receiving unit constituting the photosensor has been described. However, the present invention is not limited to this, and each light receiving unit ( If the film thickness is set so that the light absorption characteristics of the amorphous silicon film constituting the semiconductor layer correspond to each color of blue, green, and red, and each light receiving portion has a laminated structure, other The photoelectric conversion element may be applied.

<Image reading device>
Next, the overall configuration of the image reading apparatus to which the photosensor according to each of the embodiments described above can be applied will be described.
FIG. 10 is a block diagram showing an embodiment of the overall configuration of the image reading apparatus according to the present invention. In addition, about the structure equivalent to the photosensor system shown in FIG. 2, the same code | symbol is attached | subjected and the description is simplified or abbreviate | omitted.

  As shown in FIG. 10, the image reading apparatus according to the present embodiment is roughly divided into a photosensor array 100 having the same configuration as the photosensor system shown in FIG. 2, and a top gate driver (upper gate drive unit) 110. In addition to the bottom gate driver (lower gate driving means) 120 and the drain driver (precharge means, reading means) 130, a read data signal composed of an analog signal read through the drain driver 130 is digitally converted. An analog-to-digital converter (hereinafter referred to as “A / D converter”) 140 that converts an image output signal (image data) consisting of a signal, and the back side of a transparent insulating substrate SUB on which the photosensor array 100 is formed And irradiating a subject placed on the photosensor array 100 with predetermined irradiation light A controller 150 that exchanges data with an external function unit 200 that performs predetermined processing such as reading operation control of a subject image by the photosensor array 100 and collation and processing of image data. And a RAM 160 that is used as a work area of the controller 150 and temporarily stores (stores) acquired image data, processing data related to a reading operation, and the like, and a ROM 170 that holds a control program of the controller 150 and various control data. And is configured.

  Here, as the photosensor array 100, the photosensor described in each of the above-described embodiments is applied, and blue, green, and blue included in the reflected light of the light emitted from the backlight BL to the subject via the photosensor array 100, In the case where each color component of red is detected at the same timing by each light receiving unit having a laminated structure (provided in the uppermost layer, the intermediate layer, and the lowermost layer), On the other hand, a single top gate driver 110 and a bottom gate driver 120 provided in common apply a reset pulse or a readout pulse to the same row of each layer at the same time to set a reset period or a readout period at the same time. Provided with column switches, which will be described later, individually provided corresponding to the light-receiving sections of each layer (that is, each color component of blue, green, and red) The drain driver 130, along with the full precharge period a precharge voltage is applied to the columns of each layer is set at the same time, the drain voltage from all columns of each layer in the read period are read out at the same time a separate column switch.

  For example, the drain driver 130 has a configuration including a single precharge switch (precharge unit) 132 and a column switch (readout unit) 131 and an amplifier 133 provided separately for each layer. In the precharge period, based on a drain control signal (precharge signal) supplied from the controller 150, a precharge switch 132 applies a predetermined precharge pulse (precharge pulse) to the drain line Ld of each column of each layer. The charge voltage Vpg) is applied all at once, and in the reading period, the voltage (drain voltage VD) of the drain line Ld of each column is read in a batch by the column switch 131 provided for each layer, and is passed through the amplifier 133. Read data for each color component having a predetermined signal level. And outputs to the controller 150 as a signal (serial signal).

Therefore, the image reading apparatus according to the present embodiment has an element structure in which three layers of double-gate photosensors are stacked so as to overlap each other as photosensors arranged two-dimensionally in the photosensor array. In addition, the thickness of the amorphous silicon film constituting the semiconductor layer of the double-gate photosensor of each layer, or the total thickness of the amorphous silicon film up to the semiconductor layer is converted into each color component of blue, green, and red. By setting so as to have a corresponding light absorption characteristic, it is possible to achieve a spectral sensitivity characteristic equivalent to that when a color filter is applied. The blue, green, and red components contained in the reflected light can be detected simultaneously at the same time, and the subject image is in high-definition color. It can be read quickly as an image.
In addition, by applying a double gate type photosensor as the photosensor, the element structure can be reduced in size and thickness. Therefore, it is possible to relatively easily realize downsizing of the system and high definition of the read image. it can.

It is a schematic sectional drawing which shows the element structure of the double gate type photosensor applicable to the image reading apparatus which concerns on this invention. It is a schematic block diagram of the photosensor system to which a double gate type photosensor is applied. It is a timing chart which shows an example of the drive control method of the photo sensor system to which a double gate type photo sensor is applied. It is a schematic sectional drawing which shows 1st Embodiment of the element structure of the photosensor which concerns on this invention. It is a conceptual diagram which shows the light absorption state of each light-receiving part in the photosensor which concerns on this embodiment. It is a figure for demonstrating the relationship between the film thickness of the amorphous silicon film applied to the photosensor which concerns on this embodiment, and an absorption wavelength. It is a characteristic view which shows the relationship between the wavelength of the light in an amorphous silicon film, and a light absorption coefficient. It is a schematic sectional drawing which shows 2nd Embodiment of the element structure of the photosensor which concerns on this invention. It is a schematic sectional drawing which shows 3rd Embodiment of the element structure of the photosensor which concerns on this invention. 1 is a block diagram illustrating an embodiment of an overall configuration of an image reading apparatus according to the present invention.

Explanation of symbols

PSA to PSF Double gate type photosensor SUB Insulating substrate DTC detection surface 11a to 11f Semiconductor layer TGa to TGd Top gate electrode BGa to BGf Bottom gate electrode 100 Photosensor array 110 Top gate driver 120 Bottom gate driver 130 Drain driver

Claims (20)

In a photosensor that detects light of a plurality of color components corresponding to a color image of a subject by a light receiving means provided on a transparent insulating substrate, converts the light into an electrical signal, and outputs the electrical signal.
The light receiving means includes a plurality of light receiving portions having light reception sensitivity corresponding to each of the light of the plurality of color components,
The plurality of light receiving portions have a thin film transistor structure, and are formed on the insulating substrate so as to be stacked so that planar extensions overlap each other. 2. The photosensor according to claim 1, wherein the plurality of light receiving portions have light receiving sensitivities with respect to light of the respective color components set by a film thickness of a semiconductor layer constituting a channel region of the thin film transistor. 3. The photosensor according to claim 2, wherein the semiconductor layer constituting the channel region of the thin film transistor is formed of an amorphous silicon film. The plurality of light receiving units include at least a first light receiving unit set to have a high light receiving sensitivity with respect to light of a color component having a first wavelength band in the light of each color component, and a color component having a second wavelength band. The second light receiving unit set with a high light receiving sensitivity to light and the third light receiving unit set with a high light receiving sensitivity with respect to light of a color component having the third wavelength band are stacked. The photosensor according to claim 1. The first and second light receiving portions each have a drain electrode and a source electrode formed with the semiconductor layer interposed therebetween, and a transparency formed through a transparent insulating film above the semiconductor layer. A double gate type thin film transistor structure comprising: an upper gate electrode made of an electrode material having an upper gate electrode; and a lower gate electrode made of a transparent electrode material formed through a transparent insulating film below the channel region. Have
The third light receiving portion is made of a drain electrode and a source electrode formed with the semiconductor layer interposed therebetween, and a transmissive electrode material formed through a transmissive insulating film above the semiconductor layer. It has a double gate type thin film transistor structure having an upper gate electrode and a lower gate electrode made of a light-shielding electrode material formed through a transparent insulating film below the channel region. The photosensor according to claim 4. 6. The drain electrode and the source electrode constituting the first to third light receiving portions are each made of an amorphous silicon film and formed integrally with the semiconductor layer. Photo sensor. The center wavelength of the first wavelength band is 450 nm, the center wavelength of the second wavelength band is 550 nm, and the center wavelength of the third wavelength band is 600 nm. Item 7. The photosensor according to any one of Items 4 to 6. In the photosensor, the film thickness of the semiconductor layer constituting the first light receiving part is set to 50 nm, the film thickness of the semiconductor layer constituting the channel region of the second light receiving part is set to 150 nm, The film thickness of the semiconductor layer constituting the channel region of the third light receiving portion is set to 300 nm, and the light sequentially passes through the semiconductor layers constituting the first to third light receiving portions. The photosensor according to claim 7. The photosensor includes an adjustment layer made of an amorphous silicon film at least between the first and second light receiving portions and between the second and third light receiving portions. The photosensor according to any one of 4 to 7. In the photosensor, the total thickness of the amorphous silicon film through which the light from the subject is transmitted is 50 nm including the semiconductor layer constituting the first light receiving unit in the first light receiving unit. And the second light receiving portion is set to 200 nm including the semiconductor layer constituting the first light receiving portion, the adjustment layer, and the semiconductor layer constituting the second light receiving portion. In the third light receiving portion, the semiconductor layer constituting the first light receiving portion, the adjustment layer, the semiconductor layer constituting the second light receiving portion, and the semiconductor layer constituting the third light receiving portion The photosensor according to claim 9, wherein the photosensor is set to 500 nm including 11. The photosensor according to claim 9, wherein film thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be the same. A photosensor array in which a plurality of photosensors are arranged, and light of a plurality of color components corresponding to a color image of the subject is detected by the photosensor among light reflected from a desired subject. In the image reading device that reads as an electrical signal corresponding to the color image,
Each of the photosensors includes a plurality of light receiving units each having a light receiving sensitivity corresponding to each of the light of the plurality of color components,
The image reading apparatus, wherein the plurality of light receiving portions have a thin film transistor structure and are stacked on the insulating substrate so that planar spreads overlap each other. In the plurality of light receiving portions, a semiconductor layer constituting a channel region of the thin film transistor is formed of an amorphous silicon film, and the light receiving sensitivity to the light of each color component is set by the film thickness of the amorphous silicon film. The image reading apparatus according to claim 12. The image reader is at least
Upper gate driving means for outputting a control signal for simultaneously setting the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array to a reset state;
Lower gate driving means for outputting a control signal for simultaneously setting the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array to a read state;
Precharge means for outputting a control signal for simultaneously setting the plurality of light receiving portions of the plurality of photosensors arranged in the photosensor array to a precharge state;
The electrical signals generated by detecting the light of each color component corresponding to the color image of the subject from the plurality of light receiving units of the plurality of photosensors arranged in the photosensor array, for each color component Reading means for individually reading,
The image reading apparatus according to claim 12, further comprising: The plurality of light receiving units include at least a first light receiving unit set to have a high light receiving sensitivity with respect to light of a color component having a first wavelength band in the light of each color component, and a color component having a second wavelength band. The second light receiving unit set with a high light receiving sensitivity to light and the third light receiving unit set with a high light receiving sensitivity with respect to light of a color component having the third wavelength band are stacked. The image reading apparatus according to claim 12. Each of the first to third light receiving portions includes at least a drain electrode and a source electrode formed with the semiconductor layer interposed therebetween, and an upper portion formed above the semiconductor layer via a transparent insulating film. 16. The semiconductor device according to claim 15, further comprising a double gate type thin film transistor structure having a gate electrode and a lower gate electrode formed through a transparent insulating film below the channel region. Image reading device. The center wavelength of the first wavelength band is 450 nm, the center wavelength of the second wavelength band is 550 nm, and the center wavelength of the third wavelength band is 600 nm. Item 15. The image reading device according to Item 15 or 16. In the photosensor, the total thickness of the amorphous silicon film through which the light reflected by the subject is transmitted is 50 nm including the semiconductor layer constituting the first light receiving portion in the first light receiving portion. In the second light receiving part, the first light receiving part is set to 200 nm including the semiconductor layers constituting the first and second light receiving parts, and in the third light receiving part, the first to 18. The image reading apparatus according to claim 15, wherein the image reading apparatus is set to 500 nm including the semiconductor layer constituting the third light receiving unit. 19. The image reading apparatus according to claim 18, wherein the thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be different from each other. 19. The image reading apparatus according to claim 18, wherein the thicknesses of the semiconductor layers constituting the first to third light receiving portions are set to be the same.

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