JP4154555B2 - Photosensor array and two-dimensional image reader - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photosensor array and a two-dimensional image reading device, and in particular, a photosensor array configured by two-dimensionally arranging photoelectric conversion elements (photosensors) using thin film transistors having a double gate structure, and the photosensor. The present invention relates to a two-dimensional image reading apparatus using an array.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a structure having a photosensor array configured by arranging photoelectric conversion elements (photosensors) in a matrix form as a two-dimensional image reading device that reads a printed matter, a photograph, or the shape of fine irregularities such as fingerprints There are things. In general, a solid-state imaging device such as a CCD (Charge Coupled Device) is used as such a photosensor array.
[0003]
As is well known, a CCD has a configuration in which photosensors such as photodiodes and thin film transistors (TFTs) are arranged in a matrix, and is generated corresponding to the amount of light irradiated to the light receiving portion of each photosensor. The amount of electron-hole pairs (charge amount) is detected by a horizontal scanning circuit and a vertical scanning circuit, and the brightness of the irradiation light is detected.
In such a photosensor system using a CCD, it is necessary to individually provide a selection transistor for selecting each scanned photosensor, so that the system itself increases in size as the number of pixels increases. Has the problem.
[0004]
Therefore, in recent years, as a configuration for solving such problems, a thin film transistor having a so-called double gate structure (hereinafter referred to as a double gate type photosensor) in which the photosensor itself has a photosense function and a select transistor function. ) Is applied to an image reading apparatus to try to reduce the size of the system and increase the density of pixels.
[0005]
In general, an image reading apparatus using such a photosensor forms a photosensor array by forming a double gate type photosensor having a top gate electrode and a bottom gate electrode on one side of a glass substrate in a matrix. For example, irradiation light is irradiated from a light source provided on the back side of the glass substrate, and reflected light corresponding to an image pattern of a two-dimensional image such as a fingerprint from a finger placed on the detection surface above the photosensor array The light is detected as light / dark information by a double gate type photosensor, and a two-dimensional image is read.
[0006]
Here, the image reading operation by the photosensor array is performed by the carrier (correction) stored in each double-gate photosensor during the light accumulation period from the end of initialization by applying the reset pulse until the reading pulse is applied. Brightness / darkness information is detected based on the accumulated amount of holes). Note that specific configurations and operations of the double-gate photosensor and the photosensor array will be described later.
[0007]
[Problems to be solved by the invention]
By the way, in the photo sensor system applied to the two-dimensional image reading apparatus as described above, for example, a-Si that excites the difference in reflection of irradiated light due to unevenness of a finger or the like when a visible light wavelength region is incident. Detection is performed using carriers generated in the semiconductor layer, and the top gate electrode for accumulating the carriers is interposed between the test object such as a finger and the semiconductor layer, so that the reflected light is transmitted. Therefore, a transparent electrode such as ITO must be used. The top gate electrode is formed integrally with the top gate line for connecting to the terminal of the drive circuit. However, since ITO generally has a high resistivity, it tends to cause a signal propagation delay when used as a wiring. was there.
[0008]
In addition to the top gate line, the double gate transistor includes a drain line connected to the drain electrode, a source line connected to the source electrode (ground line), a bottom gate line connected to the bottom gate electrode, and a number of wirings. Therefore, there is a problem that the delay is more likely due to the overlapping capacity between the top gate line and the top gate line.
[0009]
Accordingly, an object of the present invention is to solve the above-described problems, to provide a photosensor array and a two-dimensional image reading device that can suppress signal delay and can be driven satisfactorily.
[0010]
[Means for Solving the Problems]
2. The photosensor array according to claim 1, wherein a semiconductor layer that generates carriers by excitation light, source and drain electrodes respectively provided at both ends of the semiconductor layer, and a first gate insulating film are provided below the semiconductor layer. A plurality of photoelectric conversion elements each provided with a first gate electrode provided and a second gate electrode provided above the semiconductor layer with a second gate insulating film interposed therebetween, and spaced apart from each other in a predetermined direction A first gate line that connects the first gate electrodes of each photoelectric conversion element, and a second gate line that connects the second gate electrode of each photoelectric conversion element, The second gate line has a region branched into two, and does not overlap the first gate line in the region. It is characterized by that.
[0011]
According to the first aspect of the present invention, since there is a portion that does not overlap between the first gate line and the second gate line, the parasitic capacitance generated between the first gate line and the second gate line can be reduced. Therefore, it is possible to quickly output a signal by suppressing variations in applied voltage to the first gate line or the top of the second gate line and a delay of a read operation signal, and to suppress a reduction in signal potential due to parasitic capacitance. Therefore, a better image reading operation can be realized.
Further, according to the invention of claim 2, it is possible to configure the effective region where the excitation light between the source and drain electrodes of the semiconductor layer is incident so as to easily satisfy a predetermined shape ratio. Arbitrary arrangement can be made so as to improve the bias of the light detection region. Therefore, since the effective incident area of the semiconductor layer can be set to have an optimal shape ratio, a sufficient source-drain current can flow even if the incident amount of excitation light is very small, and good light receiving sensitivity. Can be realized.
In the photoelectric conversion element, source electrodes of the plurality of semiconductor layers may be connected to each other, and drain electrodes of the plurality of semiconductor layers may be connected to each other.
[0012]
3. The photosensor array according to claim 2, wherein the source electrodes of the plurality of semiconductor layers may be connected to each other, the drain electrodes of the plurality of semiconductor layers may be connected to each other, and the source electrode or the drain electrode may be connected to the plurality of semiconductor layers. It may be formed across two adjacent ones.
In addition, the plurality of semiconductor layers of each of the plurality of photoelectric conversion elements may be arranged side by side in the channel length direction of the semiconductor layer.
[0013]
Furthermore, if a plurality of photoelectric conversion elements are arranged in a delta arrangement, the distance between the two-dimensionally adjacent photoelectric conversion elements can be made more uniform, so that the same subject is at a different angle in plan with respect to the photosensor array. Since the shift of optical information due to non-uniformity of the light receiving sensitivity that differs depending on the direction when placed on the camera can be suppressed, the angle on which the subject is placed can be reduced and the image reading characteristics can be further improved. An excellent photosensor array can be realized.
[0014]
9. The two-dimensional image reading device according to claim 8, wherein the two-dimensional image reading device is provided at each end of each of the semiconductor layers that generate carriers by excitation light, and defines an effective incident area of the excitation light in the semiconductor layer. A source and drain electrode; a first gate electrode provided below the semiconductor layer via a first gate insulating film; and a second gate electrode provided above the semiconductor layer via a second gate insulating film; A plurality of photoelectric conversion elements each including: a first gate line connected to the first gate electrode of the photoelectric conversion element; a second gate line connected to the second gate electrode of the photoelectric conversion element; A drain line connected to the drain electrode of the photoelectric conversion element; a first gate driver connected to the first gate line; and a second gate connected to the second gate line. Has a DOO driver, which is connected to a drain line, and a switch for reading the voltage is displaced in response to the incidence of the excitation light to the photoelectric conversion element, The second gate line has a region branched into two, and does not overlap the first gate line in the region. It is characterized by that.
[0015]
9. The two-dimensional image reading apparatus according to claim 8, wherein each photoelectric conversion element is arbitrarily selected by the first gate driver and the second gate driver, and the switch reads the voltage of the drain line displaced by each photoelectric conversion element. Since the delay of signal propagation can be suppressed, matrix driving can be performed quickly and accurately even if the number of photoelectric conversion elements is enormous, and a good two-dimensional image can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a photoelectric conversion element, a photosensor array, and a two-dimensional image reading apparatus according to the present invention will be described in detail below.
First, a double gate type photosensor applied to an image reading apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing the structure of a double gate type photosensor.
[0017]
As shown in FIG. 1A, a double-gate photosensor 10 includes a semiconductor layer (channel layer) 11 such as amorphous silicon in which electron-hole pairs are generated when visible light is incident, and a semiconductor layer 11. N provided at both ends of each ⁺ Silicon layers 17, 18 and n ⁺ Source electrode 12 and drain electrode 13 that are opaque to visible light, such as chromium, chromium alloy, aluminum, aluminum alloy, etc., formed on silicon layers 17, 18, and block insulating film 14 above semiconductor layer 11 (upward in the drawing). And a top gate electrode 21 made of ITO (Indium-Tin-Oxide) formed through the upper (top) gate insulating film 15 and having transparency to visible light; And a bottom gate electrode 22 that is opaque to visible light, such as chromium, chromium alloy, aluminum, aluminum alloy, or the like, which is formed via a lower (bottom) gate insulating film 16 (lower in the drawing). .
[0018]
In FIG. 1A, the top gate electrode 21, the top gate insulating film 15, the bottom gate insulating film 16, and the protective insulating film 20 provided on the top gate electrode 21 all excite the semiconductor layer 11. The bottom gate electrode 22 is made of a material that blocks the transmission of visible light while being made of a material having a high transmittance with respect to visible light. Have.
[0019]
That is, the double-gate photosensor 10 uses the semiconductor layer 11 as a common channel region, the upper MOS transistor formed by the semiconductor layer 11, the source electrode 12, the drain electrode 13, and the top gate electrode 21, the semiconductor layer 11, and the source. A structure in which two MOS transistors including a lower MOS transistor formed by the electrode 12, the drain electrode 13, and the bottom gate electrode 22 are combined is formed on a transparent insulating substrate 19 such as a glass substrate.
Such a double gate type photosensor 10 is generally represented by an equivalent circuit as shown in FIG. Here, TG is a top gate terminal, BG is a bottom gate terminal, S is a source terminal, and D is a drain terminal.
[0020]
Next, a photo sensor system configured by two-dimensionally arranging the above-described double gate type photo sensors will be briefly described with reference to the drawings.
FIG. 2 is a schematic configuration diagram of a photosensor system configured by two-dimensionally arranging double gate type photosensors.
As shown in FIG. 2, the photosensor system is roughly divided into a photosensor array 100 in which a large number of double-gate photosensors 10 are arranged in a matrix of, for example, n rows × m columns, and each double-gate photosensor. 10 top gate terminals TG (top gate electrode 21) and bottom gate terminal BG (bottom gate electrode 22) connected in the row direction, respectively, and top gate line 101 and bottom gate line 102 The top gate driver 111 and the bottom gate driver 112 connected to each other, the drain line 103 connecting the drain terminal D (drain electrode 13) of each double gate type photosensor in the column direction, and the column connected to the drain line 103 Switch 113 and source terminal Configured to include a source line 104 connected to (source electrode 12) in the column direction ground, the. The top gate line 101 is formed of ITO together with the top gate electrode 21, and the bottom gate line 102, the drain line 103, and the source line 104 are made of the same material and integrated with the bottom gate electrode 22, the drain electrode 13, and the source electrode 12, respectively. Is formed. Here, φtg and φbg are control signals for generating reset pulses φT1, φT2,... ΦTi,... ΦTn and read pulses φB1, φB2,. This is a precharge signal for controlling the timing of application.
[0021]
In such a configuration, a photo sensing function is realized by applying a voltage from the top gate driver 111 to the top gate terminal TG, and a voltage is applied from the bottom gate driver 112 to the bottom gate terminal BG, via the drain line 103. The selective readout function is realized by taking the detection signal into the output circuit unit 113 and outputting it as serial data or paradata (Vout).
[0022]
Next, a drive control method for the above-described photosensor system will be described with reference to the drawings.
FIG. 3 is a timing chart showing an example of a drive control method of the photo sensor system, FIG. 4 is an operation conceptual diagram of a double gate type photo sensor, and FIG. 5 is a light response characteristic of an output voltage of the photo sensor system. FIG.
First, in the reset operation, as shown in FIGS. 3 and 4A, a pulse voltage (reset pulse; for example, a high level of Vtg = + 15V) φTi is applied to the top gate line 101 of the i-th row, Carriers (here, holes) accumulated in the vicinity of the interface between the semiconductor layer 11 of each double-gate photosensor 10 and the semiconductor layer 11 in the block insulating film 14 are released (reset period Treset).
[0023]
Next, in the optical storage operation, as shown in FIGS. 3 and 4B, the reset operation is completed by applying a low level (for example, Vtg = −15 V) bias voltage φTi to the top gate line 101. Then, the light accumulation period Ta by the carrier accumulation operation starts. In the light accumulation period Ta, electron-hole pairs generated in the semiconductor layer 11 are generated according to the amount of light incident from the top gate electrode side, and the vicinity of the interface between the semiconductor layer 11 and the block insulating film 14 with the semiconductor layer 11 is generated. That is, holes are accumulated around the channel region.
[0024]
In the precharge operation, as shown in FIGS. 3 and 4 (c), a predetermined voltage (precharge voltage) Vpg is applied to the drain line 103 based on the precharge signal φpg in parallel with the optical storage period Ta. Is applied to hold the charge in the drain electrode 13 (precharge period Tprch).
Next, in the read operation, as shown in FIGS. 3 and 4D, after the precharge period Tprch has elapsed, a high level (for example, Vbg = + 10 V) bias voltage (read selection signal; By applying φBi (hereinafter referred to as a read pulse), the double gate photosensor 10 is turned on (read period Tread).
[0025]
Here, in the read period Tread, carriers (holes) accumulated in the channel region work in a direction to relax Vtg (−15 V) applied to the reverse polarity top gate terminal TG. An n-channel is formed by Vbg, and the drain line voltage VD of the drain line 103 tends to gradually decrease with time from the precharge voltage Vpg as shown in FIG.
[0026]
That is, when the light accumulation state in the light accumulation period Ta is dark and carriers (holes) are not accumulated in the channel region, as shown in FIGS. 4 (e) and 5 (a), the top gate By applying a negative bias to TG, the positive bias of the bottom gate BG is canceled, the double-gate photosensor 10 is turned off, and the drain voltage, that is, the voltage VD of the drain line 103 is held almost as it is. Become.
[0027]
On the other hand, when the light accumulation state is a bright state, as shown in FIGS. 4D and 5A, carriers (holes) corresponding to the amount of incident light are trapped in the channel region. The double gate type photosensor 10 is turned on by the positive bias of the bottom gate BG by acting to cancel the negative bias of the gate TG. Then, the voltage VD of the drain line 103 decreases according to the ON resistance corresponding to the amount of incident light.
[0028]
Therefore, as shown in FIG. 5A, the change tendency of the voltage VD of the drain line 103 is that the read pulse φBi is applied to the bottom gate BG from the end of the reset operation by applying the reset pulse φTi to the top gate TG. It is deeply related to the amount of light received in the time until application (light accumulation period Ta), and shows a tendency to decrease slowly when the number of accumulated carriers is small, and is steep when there are many accumulated carriers. Shows a tendency to decrease. Therefore, the time until reaching the voltage is detected by detecting the voltage VD of the drain line 103 after the elapse of a predetermined time from the start of the read period Tread or based on the predetermined threshold voltage. By doing so, the amount of irradiation light is converted.
[0029]
The above-described series of image reading operations is set as one cycle, and the double gate photosensor 10 is operated as a two-dimensional sensor system by repeating the same processing procedure for the i + 1th row double gate photosensor 10. Can do.
In the timing chart shown in FIG. 3, after the precharge period Tprch has elapsed, a low level (for example, Vbg = 0 V) is applied to the bottom gate line 102 as shown in FIGS. Is continued, the double gate type photosensor 10 is kept in the OFF state, and the voltage VD of the drain line 103 maintains the precharge voltage Vpg as shown in FIG. 5B. As described above, the selection function of selecting the readout state of the double gate type photosensor 10 is realized by the application state of the voltage to the bottom gate line 102.
[0030]
FIG. 6 is a cross-sectional view of a main part of a two-dimensional image reading apparatus to which the above-described photosensor system is applied.
As shown in FIG. 6, in an image reading apparatus that reads a two-dimensional image such as a fingerprint, from a backlight (surface light source) 30 provided on the lower side of a glass substrate (insulating substrate) 19 of a double gate type photosensor 10. The irradiation light R1 is incident, and the irradiation light R1 passes through the transparent insulating substrate 19 and the insulating films 15, 16, and 20 except for the formation region of the double-gate photosensor 10, and the subject on the protective insulating film 20 40 is irradiated.
[0031]
Then, the reflected light R2 corresponding to the reflectance (brightness information) determined by the image pattern (or uneven pattern) of the subject 40 passes through the transparent insulating films 20, 15, 14 and the top gate electrode 21, and the semiconductor layer 11 , The carrier corresponding to the image pattern of the subject 40 is accumulated, and the image pattern of the subject 40 can be read as light / dark information according to the series of drive control methods described above.
[0032]
Next, a photoelectric conversion element, a photosensor array, and a two-dimensional image reading apparatus according to the present invention will be described with reference to the drawings. In the embodiment described below, the above-mentioned double gate type photosensor is applied as a photoelectric conversion element (photosensor), and a photofunction is provided by applying a voltage using the top gate electrode as a first gate electrode. A description will be given assuming that the function of reading the amount of charge accumulated in the channel region is realized by applying a voltage using the bottom gate electrode as the second gate electrode.
[0033]
7 and 10 are schematic configuration diagrams showing a double gate type photosensor applied to the photosensor array according to the present invention. Here, FIG. 7 is a sectional view taken along line AA of FIG. 10 described later.
As shown in FIG. 7, the double-gate photosensor 10A according to this embodiment includes semiconductor layers 11a and 11b made of amorphous silicon or the like that generate electron-hole pairs when visible light arranged in parallel is incident thereon. N provided at both ends of each of the semiconductor layers 11a and 11b ⁺ N between the silicon layers 17a, 17b and 18a, 18b and the respective semiconductor layers 11a, 11b ⁺ A single drain electrode 13 formed over the silicon layers 18a and 18b and n facing the drain electrode 13 across the semiconductor layers 11a and 11b. ⁺ The individual source electrodes 12a and 12b formed on the silicon layers 17a and 17b, and the respective semiconductor layers via the block insulating films 14a and 14b and the top gate insulating film 15 above the semiconductor layers 11a and 11b (upward in the drawing). A single top gate electrode 21 formed in common to 11a and 11b and a bottom gate insulating film 16 below each semiconductor layer 11a and 11b (downward in the drawing) to each semiconductor layer 11a and 11b And a single bottom gate electrode 22 formed in common, and these structures are formed on an insulating substrate 19 such as a glass substrate.
[0034]
Here, as shown in FIG. 10, the source electrodes 12a and 12b are formed so as to protrude from the common source wiring 12M along the longitudinal direction (the horizontal direction in the drawing) of the semiconductor layers 11a and 11b in a comb shape, The drain electrode 13 is formed to protrude from the drain wiring 13M facing the source wiring 12M in the direction of the source wiring 12M along the longitudinal direction of the semiconductor layers 11a and 11b (the horizontal direction in the drawing). That is, the source electrodes 12a and 12b and the drain electrode 13 are formed so as to be opposed to each other with the individual semiconductor layers 11a and 11b interposed therebetween.
[0035]
In FIG. 7, the protective insulating film 20 provided on the block insulating films 14a and 14b, the top gate insulating film 15, the bottom gate insulating film 16, and the top gate electrode 21 is a light-transmitting insulating film such as silicon nitride. Further, the top gate electrode 21 and the top gate line 101 are made of a light-transmitting material such as ITO, and both show high transmittance for visible light. On the other hand, at least the bottom gate electrode 22 and the bottom gate line 102 are made of a material that blocks transmission of light such as Cr.
[0036]
That is, the double gate type photosensor 10A has a first upper portion formed by the semiconductor layer 11a, the source electrode 12a, the drain electrode 13, the top gate insulating film 15, and the top gate electrode 21, with the semiconductor layer 11a as a common channel region. A first double-gate photosensor comprising a MOS transistor and a first lower MOS transistor formed by a semiconductor layer 11a, a source electrode 12a, a drain electrode 13, a bottom gate insulating film 16 and a bottom gate electrode 22, and The second upper MOS transistor formed of the semiconductor layer 11b, the source electrode 12b, the drain electrode 13, the top gate insulating film 15, and the top gate electrode 21, the semiconductor layer 11b, the source Electrode 12b, drain electrode 13 A configuration in which a second double-gate photosensor composed of a second lower MOS transistor formed by the bottom gate insulating film 16 and the bottom gate electrode 22 is connected in parallel is formed on the insulating substrate 19. ing.
[0037]
In particular, the top gate electrode 21 and the bottom gate electrode 22 constituting the first and second double gate type photosensors are each constituted by a common electrode, and the source electrodes 12a and 12b are formed so as to protrude from the common source wiring 12M. Therefore, the semiconductor layer serving as the photosensor portion has two double-gate photosensors per element, and the above-described drive control method is applied to each semiconductor layer. It can be operated in the same manner as a double gate type photosensor.
[0038]
Here, regarding the relationship between the shape of the substantial incident region (incidence effective region) of the excitation light to the semiconductor layer in the double-gate photosensor having the above-described configuration and the light receiving sensitivity of the double-gate photosensor, The photoelectric conversion element (double gate type photosensor) according to the present invention will be described in detail while comparing with the structure of one semiconductor layer.
[0039]
FIG. 8A is a diagram showing an effective incidence area of a double-gate photosensor having one semiconductor layer as a photosensor unit per element shown in FIG. 1, and FIG. 8B is a photosensor. FIG. 9 is a conceptual diagram showing variation in light receiving sensitivity (distribution characteristics; hereinafter referred to as “expansion of photodetection region”) in the configuration shown in FIG. 8A. FIG. 10 is a schematic diagram showing the incidence effective region of a double gate type photosensor having two semiconductor layers as a photo sensor unit per element from above, and FIG. 11 is a diagram showing the double gate type photo sensor shown in FIG. FIG. 12 is a schematic diagram showing the spread of a light detection region in a sensor. FIG. 12 is a photosensor array in which a double gate type photosensor having three semiconductor layers serving as a photosensor unit per element is arranged in a matrix. It is a plan view of a. Here, the spread of the light detection region shown in FIG. 9 and FIG. 11 schematically shows a region where a predetermined light receiving sensitivity can be obtained around the semiconductor layer (specifically, the channel region), It does not strictly indicate the light receiving sensitivity distribution range.
[0040]
In the photosensor arrays 100 and 100A shown in FIGS. 8 and 12, each top gate line 101 connects between the top gate electrodes 21 of the double gate type photosensors 10 and 10A arranged for each row, and a bottom gate. A line 102 connects between the bottom gate electrodes 22 of the double-gate photosensors 10 and 10A arranged for each row. The top gate line 101 and the bottom gate line 102 in the same row are formed so as not to overlap each other between adjacent double gate type photosensors 10 (or 10A) (to avoid overlapping).
[0041]
That is, the top gate line 101 branched into two vertically above and below in the column direction of one bottom gate line 102 is arranged so as not to overlap the bottom gate line 102. With such a configuration, since the conductive layers constituting the top gate line 101 and the bottom gate line 102 do not face each other, the parasitic capacitance generated between the top gate line 101 and the bottom gate line 102 can be reduced. Further, it is possible to realize a better image reading operation by suppressing variations in applied voltages to the top gate line 101 and the bottom gate line 102 and delays in the reading operation signal.
[0042]
Further, the drain current Ids flowing according to the amount of light can be defined as follows.
Ids ∝ W / L (1)
Here, as shown in FIGS. 1 and 8, W and L are the channel width and channel length of the semiconductor layer, respectively. In order to read the displacement of the precharged drain voltage, the ratio W / L is desirably 3.0 or more, and more desirably 7.0 or more. In general, when the double gate photosensor as described above is used to function as a photosensor that accumulates electric charges according to excitation light incident from the outside, the light receiving sensitivity thereof is the source and drain electrodes 12 and 13. It has been found that it depends greatly on the shape of the incident effective region of the excitation light incident on the semiconductor layer exposed from the surface, that is, substantially the length of the semiconductor layer in the channel length L direction and the channel width W direction.
[0043]
Since the source and drain electrodes 12 and 13 are opaque to visible light, the incident effective region, which is a region where carriers effective for the drain current Ids are formed, in the semiconductor layer 11 is between the source and drain electrodes 12 and 13. The region is surrounded by a distance K between the source and drain electrodes 12 and 13 in the x direction and a channel width W in the y direction.
[0044]
Thus, the sensitivity region of the photosensor depends on the channel width W and the length K in the channel length direction, and the source-drain current value Ids of the transistor is a ratio of the channel width W and the channel length L of the semiconductor layer 11. Therefore, in order to improve the drain current of the double gate type photosensor 10, it is necessary to design the design value of the ratio W / L as large as possible, but when the ratio W / L is increased, FIG. In the double-gate photosensor of FIG. 8, the planar structure inevitably has a length W in the channel width direction (or a dimension in the longitudinal direction of the semiconductor layer 11) and a length K in the channel length direction (or The dimension of the semiconductor layer 11 in the width direction becomes a short rectangular shape, and accordingly, the spread of the light detection region having high light receiving sensitivity is biased in the y direction compared to the x direction.
[0045]
Specifically, since the effective incident area of the semiconductor layer 11 has a rectangular shape, as shown in FIG. 9, the spread of the light detection area inevitably extends in the longitudinal direction of the semiconductor layer 11 (the vertical direction in the drawing; y In the horizontal direction (x direction) of the drawing, the region where the desired light receiving sensitivity is obtained is relatively relative to the y direction. Narrow.
Therefore, the light / dark information (read image) from the subject is read in a distorted state due to the uneven spread of the light detection region in the x and y directions, and the image information with high light receiving sensitivity and distortion is suppressed. There is a problem that it is impossible to simultaneously read data.
[0046]
Note that the planar configuration of the photosensor array 100 constituted by such a double gate type photosensor 10 is, for example, x, y in which the double gate type photosensors 10 are orthogonal to each other as shown in FIG. In two directions (row and column directions) at predetermined pitches Psp and arranged in a lattice (matrix) shape at equal intervals, and further from the surface of the insulating substrate (glass substrate) through the inter-element region Rp inside the lattice. Consideration is given so that the subject is irradiated with light. Therefore, in order to irradiate the subject with a sufficient amount of light, it is necessary to secure the inter-element region Rp as large as possible.
[0047]
On the other hand, in the double gate type photosensor 10A according to the present embodiment, as shown in FIG. 10, two semiconductor layers 11a and 11b are connected in parallel with the width direction (longitudinal direction) facing each other. Therefore, the source electrodes 12a and 12b and the drain electrode 13 make the effective width of the incident regions in the semiconductor layers 11a and 11b W in the channel width direction, and the lengths in the channel length direction K1 and K2, respectively. In this case, the longitudinal dimension (length in the channel width direction) of the incident effective region of the semiconductor layers 11a and 11b is maintained at “W”, and the width dimension (length in the channel length direction) of the incident effective region of the semiconductor layer 11a. Can be handled as a double-gate photosensor obtained by adding (K1 + K2). Therefore, the light receiving sensitivity depends on the ratio W / (K1 + K2) between the length W in the channel width direction and the total length (K1 + K2) in the channel length direction.
[0048]
In this case, the shape of the incident effective region in each of the semiconductor layers 11a and 11b (the combined shape of the rectangular region having the length W × K1 and the rectangular region having the length W × K2) approximates a square shape. As a result, the variation in the light receiving sensitivity due to the incident angle of the excitation light to the semiconductor layers 11a and 11b is corrected.
That is, as the ratio W / (K1 + K2) between the length W in the channel width direction and the sum (K1 + K2) of the lengths in the channel length direction approaches 1, as shown in FIG. 11, the x direction (arrow A; , The sensitivity of light incident on the semiconductor layers 11a and 11b from the region having an angle of ± 45 ° with respect to the x direction, respectively, and the y direction (arrow B; more specifically, ± with the y direction as the center) The sensitivity of the light incident on the semiconductor layers 11a and 11b from the region having an angle of 45 ° is more equal, and the variation (direction) of the light receiving sensitivity is corrected. Thus, it is possible to obtain a region Ea having a substantially uniform spread (a rectangle approaching a substantially square shape) in the y direction.
[0049]
Here, in the ratio W / (K1 + K2) of the length W in the channel width direction and the sum of the lengths in the channel length direction (K1 + K2) that influences the light receiving sensitivity of the double gate type photosensor, the length in the channel length direction Can be replaced with the sum ΣKi of the length Ki in the channel length direction of the incident effective region in each semiconductor layer in accordance with the number of semiconductor layers formed in one element.
As a result of intensive studies by the inventor, the ratio W / ΣKi between the length W in the channel width direction and the total sum ΣKi in the channel length direction is 1 for leveling the directivity of the reflected light. 0.0 ≦ W / ΣKi ≦ 10 (more desirably, W / ΣKi ≦ 8.0), the variation in the light receiving sensitivity with respect to the incident angle of the excitation light to the incident effective region is appropriately suppressed and corrected. It has been found that the light receiving sensitivity is optimal.
[0050]
This is the same in the structures shown in FIGS. 8A and 8B, but it is needless to say that the directivity of incident light can be leveled compared with the case of FIG. In addition to the above conditions, in FIG. 11, two sides defined by both outer ends in the x direction and two sides defined by both outer ends in the y direction (source electrode 12a) of the incident effective regions of the plurality of semiconductor layers. And the boundary line between the incident effective region of the semiconductor layer 11a and the boundary line between the source electrode 12b and the effective incident region of the semiconductor layer 11b) is closer to the square, the viewpoint of the balance of light receiving sensitivity. More desirable from.
[0051]
Further, in the double gate type photosensor 10A shown in FIG. 10, the length (K1 = K2 = K in the channel length direction of the incident effective region in the two semiconductor layers 11a and 11b is set to be (1 ), The source-drain current Ids can theoretically be set to double that of the double-gate transistor shown in FIG. 8, so that the light receiving sensitivity can be remarkably improved.
Therefore, by arranging such a double gate type photosensor 10A in a matrix form as shown in FIG. 12 to form a photosensor array 100A, the spread of the light detection region is made uniform, and a two-dimensional image is formed. It is possible to realize a photosensor array including a light receiving unit having high light receiving sensitivity while suppressing distortion at the time of reading, and a two-dimensional image reading device.
[0052]
Further, according to the double gate type photosensor 10A described above, the light receiving sensitivity is significantly increased, so that the light / dark information reading operation can be satisfactorily performed even when the amount of incident light is small compared to the photosensor 10. Therefore, the illuminance of the surface light source attached to the reading apparatus can be reduced (suppressed), and the power consumption of the two-dimensional image reading apparatus can be reduced. Alternatively, when the illuminance of the surface light source equivalent to that of the photosensor 10A is applied, the light storage time can be greatly shortened by the improvement in the light receiving sensitivity, and a reading device with excellent two-dimensional image reading performance can be obtained. Can be provided.
[0053]
Furthermore, since the light receiving sensitivity is greatly improved, an excessive light on-current is generated for the same amount of incident light as that of the photosensor 10A. For the purpose of suppressing such on-current, the top gate and the bottom gate Operation can be controlled by lowering the drive voltage applied to both electrodes. By reducing the drive voltage, deterioration of the characteristics of the double-gate photosensor over time is suppressed, and the reliability of the photosensor array is increased. It can also be sustained (prolonged life).
[0054]
FIG. 13 is a schematic configuration diagram of another double-gate type photosensor applied to the photosensor array according to the present invention. FIG. 14 is a plan view of the photosensor array in which the double-gate type photosensors are arranged in a matrix. It is a block diagram. Here, about the structure equivalent to embodiment mentioned above, the same code | symbol is attached | subjected and the description is simplified.
[0055]
As shown in FIG. 13, the double-gate photosensor 10B according to the present embodiment is formed by connecting semiconductor layers 11a, 11b, and 11c such as amorphous silicon arranged in parallel and the semiconductor layers 11a and 11b. The single drain electrode 13a, the single source electrode 12b formed by connecting the semiconductor layers 11b and 11c, and the source electrode 12a formed facing the drain electrode 13a across the semiconductor layer 11a A drain electrode 13b formed opposite to the source electrode 12b with the semiconductor layer 11c interposed therebetween, and n interposed between the semiconductor layer 11a and the source electrode 12a ⁺ N interposed between the silicon layer 17a, the semiconductor layer 11a and the drain electrode 13a ⁺ N interposed between the silicon layer 18a, the semiconductor layer 11b, and the drain electrode 13a ⁺ N interposed between the silicon layer 17b, the semiconductor layer 11b, and the source electrode 12b ⁺ N interposed between the silicon layer 18b, the semiconductor layer 11c, and the source electrode 12b ⁺ N interposed between the silicon layer 17c, the semiconductor layer 11c, and the drain electrode 13b ⁺ A single top gate electrode formed in common to each of the semiconductor layers 11a, 11b, and 11c via the top gate insulating film 15 above the silicon layer 18c and the semiconductor layers 11a, 11b, and 11c (upward in the drawing) 21 and a single bottom gate electrode 22 formed in common to the semiconductor layers 11a, 11b, and 11c via the bottom gate insulating film 16 below the semiconductor layers 11a, 11b, and 11c (downward in the drawing). These structures are formed on an insulating substrate 19 such as a glass substrate.
[0056]
In addition, about the material of each insulating film and an electrode, and another structure, since it is equivalent to embodiment mentioned above in FIG. 1, FIG. 7, description is abbreviate | omitted.
That is, the double-gate photosensor 10B has the semiconductor layer 11a as a common channel region, the semiconductor layer 11a, the source electrode 12a, the drain electrode 13a, the top gate insulating film 15, the bottom gate insulating film 16, the top gate electrode 21, and the bottom. The semiconductor layer 11b, the source electrode 12b, the drain electrode 13a, the top gate insulating film 15, and the bottom gate insulating film 16 with the first double gate type photosensor constituted by the gate electrode 22 and the semiconductor layer 11b as a common channel region. The semiconductor layer 11c, the source electrode 12b, the drain electrode 13b, and the top gate insulating film with the second double gate type photosensor constituted by the top gate electrode 21 and the bottom gate electrode 22 and the semiconductor layer 11c as a common channel region 15. Bottom gate insulating film 1 And a third double-gate photo-sensor composed of the top gate electrode 21 and the bottom gate electrode 22, configuration linked disposed in parallel, are formed on the insulating substrate 19.
[0057]
In particular, the top gate electrode 21 and the bottom gate electrode 22 constituting each of the first to third double gate type photosensors are each constituted by a common electrode, and the source electrodes 12a and 12b protrude from the common source wiring 12M. In addition, since the drain electrodes 13a and 13b are formed so as to protrude from the common drain wiring 13M, three double-gate photosensors are applied by applying the drive control method described above. It can be operated as a double gate type photosensor.
[0058]
According to the double-gate photosensor 10A having such a configuration, the semiconductor layers 11a, 11b, and 11c constituting the channel region are connected and arranged in parallel with the width direction (longitudinal direction) facing each other. The length of the incident effective region in the channel length direction of each semiconductor layer 11a, 11b, 11c is kept at W, and the length of the incident effective region in the channel length direction is K3, K4, K5 (for example, K3 = K4 = K5 = K) and can be handled as a double gate type photosensor set to 3 times (3 × K3).
Therefore, from the above equation (1), the source-drain current Ids can theoretically be set to three times that of the double gate transistor shown in FIG. 8, so that the light receiving sensitivity can be remarkably improved.
[0059]
In addition, since the semiconductor layers 11a, 11b, and 11c are arranged in parallel with the longitudinal direction facing each other, the spread of the light detection region is further expanded in the length direction of the semiconductor layer (the vertical direction in the drawing), It can be made more square.
Therefore, similarly to the embodiment shown in FIGS. 1 and 7, the double gate type photosensor 10B is arranged in a matrix as shown in FIG. 14 to constitute the photosensor array 100B. A photosensor array including a light receiving unit having a high light receiving sensitivity, and a reading device for a two-dimensional image, which further uniformizes the spread of the light detection region and suppresses distortion during reading of the two-dimensional image. Can be realized.
[0060]
In the embodiment shown in FIGS. 1, 7, and 13, the double-gate photosensors 10, 10A, and 10B are connected in parallel by 1 to 3 semiconductor layers (or double-gate photosensors). However, the present invention is not limited to this form. Therefore, the light receiving sensitivity can be arbitrarily set according to the number of semiconductor layers to be connected and arranged.
Here, as shown in FIG. 12 or FIG. 14, when the double-gate photosensors 10A and 10B are arranged in a matrix to form the photosensor arrays 100A and 100B, and applied to a two-dimensional image reader, Since light from the insulating substrate (glass substrate) 19 side is irradiated to the subject through the inter-element regions Ra and Rb in the matrix lattice, the inter-element region Ra, After setting Rb, it is necessary to arbitrarily set the number of semiconductor layers (double gate type photosensors) connected and arranged in the formation region of the light receiving portion.
[0061]
FIG. 15 is a schematic configuration diagram showing still another embodiment of the photosensor array according to the present invention, and FIG. 16 is a schematic configuration diagram of a two-dimensional image reading apparatus to which the photosensor array according to this embodiment is applied. It is. In FIG. 16, for the convenience of illustration, a double gate type photosensor is shown in a simplified manner.
As shown in FIG. 15, the photosensor array 100C according to the present embodiment has a double-gate photosensor 10C equivalent to the embodiment shown in FIG. 10, and each double-gate photosensor 10C is two-dimensional. A so-called delta in which one side is set at each vertex position of a virtual equilateral triangle of Psa (= Psp: the pitch between the double-gate photosensors 10 shown in FIG. 8B) set continuously in a plane. It is arranged.
[0062]
That is, in contrast to the arrangement of the double gate type photosensors 10 in the photosensor array 100 shown in FIG. 8B, in the case of the photosensor array 100 in FIG. , X, y are arranged so as to be spaced apart by an equal dimension Psp only in two orthogonal directions, so that they are oblique directions (0 °, 90 °, 180 °) with respect to the x, y directions corresponding to the matrix. At an appropriate angle other than 270 ° (for example, 45 ° or 60 ° direction), the pitch between the double-gate photosensors 10 increases in the x and y directions and becomes non-uniform (for example, 45 °). In some cases, it is √2 times Psp), and there is a problem that a uniform and highly accurate reading operation cannot be realized for a subject placed in an oblique direction.
[0063]
On the other hand, in the photosensor array 100C according to the present embodiment, a double-gate photosensor 10C serving as a light receiving unit is disposed at each vertex position of each equilateral triangle set continuously in a two-dimensional plane. Therefore, the double gate type photosensors 10C are arranged equally in the x direction, and the double gate type photosensors 10C are arranged equally in the oblique directions (60 °, 120 °, 240 °, 300 °). As a result, the pitch between the light receiving parts is equalized to Psa.
[0064]
Therefore, all the double gate type photosensors arranged on the two-dimensional plane are arranged at a pitch Psa that is equidistant from the double gate type photosensors adjacent to each other in the substantially entire circumferential direction. Even when the obtained two-dimensional image is placed obliquely with respect to the x and y directions, it can be accurately read with high reading accuracy while suppressing distortion during image reading.
Since the double gate type photosensors are arranged in a delta arrangement, when the pitch in the x direction is set to Psa (= Psp) equivalent to that of the photosensor in FIG. 8B, the pitch Psb in the y direction is It is expressed by the formula.
Psb = Psa × sin60 ° (2)
[0065]
Thus, since the pitch Psb in the y direction is shorter than the pitch Psa (= Psp) in the x direction, the plane is reduced in the y direction compared to the plane region Mp of the photosensor in FIG. In the region Mc, the same number of double-gate photosensors can be arranged, and the two-dimensional image reader can be downsized. In other words, in a plane area equivalent to that of the photosensor of FIG. 8B, double the number of 1 / sin 60 ° times (≈1.15 times) compared to the photosensor configuration of FIG. A gate-type photosensor can be provided, and the density can be increased.
In the delta arrangement, the configuration shown in the embodiment of FIG. 10 is applied as the double gate type photosensor that constitutes each light receiving unit, but the embodiment shown in FIG. 8A and FIG. 13A is used. Needless to say, a double-gate photosensor having another configuration may be applied.
[0066]
In the double-gate photosensor arrays 100, 100A, 100B, and 100C described above, the top gate line 101 and the bottom gate line 102 in the same row are adjacent to the double-gate photosensors 10 (or 10A, 10B, and 10C). Any one of them is formed so as not to overlap each other in a plane (to avoid overlapping). That is, the top gate line 101 branched into two vertically below the column direction of one bottom gate line 102 is arranged so as not to overlap the bottom gate line 102.
[0067]
With such a configuration, since the conductive layers constituting the top gate line 101 and the bottom gate line 102 do not face each other, the parasitic capacitance generated between the top gate line 101 and the bottom gate line 102 can be reduced. Further, it is possible to realize a better image reading operation by suppressing variations in applied voltages to the top gate line 101 and the bottom gate line 102 and delays in the reading operation signal. In each of the above embodiments, the top gate line 101 and the bottom gate line 102 do not overlap at all between adjacent double gate type photosensors, but the wiring width of the top gate line 101 is made wider to suppress propagation delay. Thus, even if a region that does not overlap with the region partially overlapping with the bottom gate line 102 is provided, the effect of suppressing propagation delay is brought about. Conversely, it goes without saying that even if the bottom gate line 102 is provided with a region that does not overlap with the region that partially overlaps the top gate line 101, there is an effect of suppressing propagation delay.
[0068]
By applying such a photosensor array to a two-dimensional image reading apparatus (fingerprint reading apparatus in the figure) as shown in FIG. 16, the surface light source 30 provided on the glass substrate side of the photosensor array 100M is used. The reflected light of the light R that is transmitted through the transparent insulating film in the inter-element region and applied to the subject 40a such as a finger is incident on each double-gate photosensor 10M arranged in a matrix, as described above. In addition, it is possible to read the light / dark information of the subject 40a with high accuracy and in a short time while reducing distortion at the time of reading.
In addition, since the light receiving sensitivity in the photosensor array 100M can be significantly improved, the illuminance of the surface light source can be relatively reduced, and the power consumption of the reading apparatus can be reduced.
[0069]
【The invention's effect】
According to the first aspect of the invention, since there is a portion that does not overlap between the first gate line and the second gate line, it is possible to reduce the parasitic capacitance generated between the first gate line and the second gate line. Further, it is possible to realize a better image reading operation by suppressing variations in applied voltage to the first gate line or the top of the second gate line and delaying a reading operation signal.
[0070]
According to the invention described in claim 2, by providing a plurality of semiconductor layers, it can be arbitrarily arranged so as to improve the bias of the light detection region. Therefore, since the effective incident area of the semiconductor layer can be easily set to have an optimum shape ratio, even if the incident amount of excitation light is very small, a sufficient source-drain current can flow, which is favorable. Light receiving sensitivity can be realized.
In the photoelectric conversion element, source electrodes of the plurality of semiconductor layers may be connected to each other, and drain electrodes of the plurality of semiconductor layers may be connected to each other.
[0071]
Further, in the above photosensor array, if a plurality of photoelectric conversion elements are arranged in a delta arrangement, the distance between the two-dimensionally adjacent photoelectric conversion elements can be made more uniform. On the other hand, it is possible to suppress the shift of optical information due to non-uniformity of the light receiving sensitivity that differs depending on the direction when placed at different angles on a plane, so there is less restriction on the angle on which the subject is placed, It is possible to realize a photosensor array having excellent image reading characteristics. Furthermore, the reading accuracy can be improved by downsizing the reading device or increasing the density of the light receiving unit.
[0072]
According to the two-dimensional image reading apparatus according to claim 8, each photoelectric conversion element is arbitrarily selected by the first gate driver and the second gate driver, and the voltage of the drain line displaced by each photoelectric conversion element is switched by the switch. Since signal propagation delay can be suppressed when reading, matrix driving can be performed quickly and accurately even when the number of photoelectric conversion elements is enormous, and a good two-dimensional image can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a structure of a double gate type photosensor applied to the present invention.
FIG. 2 is a schematic configuration diagram of a photosensor system configured by two-dimensionally arranging double-gate photosensors applied to the present invention.
FIG. 3 is a timing chart showing an example of a drive control method of the photosensor system.
FIG. 4 is an operation conceptual diagram of a double gate type photosensor.
FIG. 5 is a diagram showing a light response characteristic of an output voltage of the photosensor system.
FIG. 6 is a cross-sectional view of a main part of a two-dimensional image reading apparatus to which the above-described photosensor system is applied.
FIG. 7 is a schematic configuration diagram showing two double-gate photosensors for each semiconductor layer serving as a photosensor unit applied to the photosensor array according to the present invention.
FIG. 8 is a diagram showing an incident effective region of a double-gate photosensor having one semiconductor layer serving as a photosensor unit per element and an arrangement structure in the photosensor array.
9 is a conceptual diagram showing variations in light receiving sensitivity of the double-gate photosensor shown in FIG.
FIG. 10 is a schematic diagram showing an incident effective region of a double-gate photosensor having two semiconductor layers serving as a photosensor unit per element.
11 is a schematic view showing the spread of a light detection region in the double-gate photosensor shown in FIG.
FIG. 12 is a plan configuration diagram of a photosensor array in which double-gate photosensors according to the present embodiment are arranged in a matrix.
FIG. 13 is a schematic configuration diagram showing another double gate type photosensor applied to the photosensor array according to the present invention.
FIG. 14 is a plan configuration diagram of a photosensor array in which double-gate photosensors according to the present embodiment are arranged in a matrix.
FIG. 15 is a schematic configuration diagram showing still another embodiment of the photosensor array according to the present invention.
FIG. 16 is a schematic configuration diagram of a two-dimensional image reading apparatus to which the photosensor array according to the present embodiment is applied.
[Explanation of symbols]
10, 10A, 10B, 10C Double gate type photo sensor
11a, 11b, 11c Semiconductor layer
12a, 12b Source electrode
13, 13a, 13b Drain electrode
14a, 14b Block insulating film
15 Top gate insulating film
16 Bottom gate insulating film
17, 18 n ⁺ Silicon layer
19 Insulating substrate
20 Protective insulating film
21 Top gate electrode
22 Bottom gate electrode
100A, 100B, 100C Photosensor array
101 Top gate line
102 Bottom gate line

Claims (8)

A semiconductor layer that generates carriers by excitation light; and
Source and drain electrodes respectively provided at both ends of the semiconductor layer;
A first gate electrode provided below the semiconductor layer via a first gate insulating film;
A second gate electrode provided above the semiconductor layer via a second gate insulating film;
A plurality of photoelectric conversion elements arranged separately from each other in a predetermined direction;
A first gate line connecting the first gate electrodes of each photoelectric conversion element;
A second gate line connecting the second gate electrodes of each photoelectric conversion element;
Have
2. The photosensor array according to claim 1, wherein the second gate line has a region branched into two, and does not overlap the first gate line in the region .   The semiconductor layer of each photoelectric conversion element is divided into a plurality of layers, and the plurality of semiconductor layers are provided with the source and drain electrodes, the source electrodes are connected to each other, and the drain electrodes are connected to each other. The photosensor array according to claim 1. Claim wherein the channel length direction of the incident effective region of the semiconductor layer to the sum of the length, the ratio of the length of the channel width direction of the incident effective region, which is characterized in that 1.0 or more and 10 or less 3. The photosensor array according to 1 or 2.   The photosensor array according to claim 1, wherein the second gate line is transmissive to visible light.   The photosensor array according to claim 1, wherein the source electrode or the drain electrode is opaque to visible light.   The photosensor array according to claim 2, wherein the plurality of semiconductor layers of each of the plurality of photoelectric conversion elements are arranged side by side in the channel length direction of the semiconductor layer.   The photosensor array according to claim 2, wherein the plurality of photoelectric conversion elements are arranged in a delta arrangement. A semiconductor layer that generates carriers by excitation light; and a source and drain electrode that are provided at both ends of each of the semiconductor layers and that define an effective incident area of the excitation light in the semiconductor layer; and a first gate insulating film A plurality of photoelectric conversion elements each including a first gate electrode provided below the semiconductor layer and a second gate electrode provided above the semiconductor layer via a second gate insulating film;
A first gate line connected to the first gate electrode of the photoelectric conversion element;
A second gate line connected to the second gate electrode of the photoelectric conversion element;
A drain line connected to the drain electrode of the photoelectric conversion element;
A first gate driver connected to the first gate line;
A second gate driver connected to the second gate line;
A switch that is connected to the drain line and reads a voltage that is displaced according to incidence of excitation light on the photoelectric conversion element;
Have
The two- dimensional image reading apparatus, wherein the second gate line has a region branched into two, and does not overlap the first gate line in the region .

Images