JP3135309B2 - Photoelectric conversion device and information processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used for an image reading apparatus such as a facsimile machine and a digital copying machine.

[0002]

2. Description of the Related Art In recent years, with the spread of so-called electronic office machines such as facsimile machines and digital copiers, there has been an increasing demand for small-sized and low-cost image reading apparatuses. Therefore, a direct-magnification type image reading apparatus which can directly contact the original held by the original holding means for holding the original at the reading position and which does not require an imaging system or has a short optical path length of the imaging system Is attracting attention. As a photoelectric conversion unit used in such an image reading device, a CCD is a typical example, but a device using a non-single-crystal semiconductor such as an amorphous silicon or CdS as a material has a low cost and a large area. The main feature is that it can be built, and development is being actively pursued.

[0003] Photoelectric conversion elements using an amorphous semiconductor are classified into a photoconductive type that allows injection of charge from an electrode and a photodiode type that does not allow injection. The photoconductive type generally has advantages of high conversion efficiency, capable of receiving a large signal, and capable of being manufactured at low cost. In addition, a so-called coplanar type photoconductive element in which a pair of source and drain electrodes forming an ohmic junction with a semiconductor has the same electrode material is a MIS capacitor for charge storage and a thin film transistor for charge transfer. Since they can be formed with a common film configuration, they also have an advantage that a signal processing unit can be simultaneously formed.

However, the photoconductive sensor has a point to be improved in that a response to a change in light input, that is, a so-called light response is several orders of magnitude slower. The reason for the slow photoresponse of the photoconductive sensor is that
For example, as described in JP-A-62-193364. Due to the slow light response, there arise problems such as difficulty in increasing the speed of the image reading device and inferior quality of the read image.

In order to solve such a problem, one of the present invention is to provide a pixel for converting optical information into electric information.
A photoelectric conversion device comprising: a photoconductive element whose conductivity is changed by receiving light; and a photocapacitance change element whose capacity is changed by receiving light, wherein one electrode of the photoconductive element is And one electrode of the photo-capacitance changing element is short-circuited, the other electrode of the photo-conductivity-type element and the other electrode of the photo-capacitance changing element are short-circuited, A surface and a light receiving surface of the optical capacitance changing element are independently juxtaposed.

According to the present invention, an optical capacitance changing element whose capacity changes in accordance with the amount of incident light outputs charges differentially with respect to the change in the amount of incident light, and the output of the photoconductive element having a slow optical response. By acting so as to compensate for the charge current in a photo-responsive manner, it is possible to produce a photoelectric conversion section with a fast photo-response.

On the other hand, the prior art has another problem to be solved. FIG. 1 shows, as an example, a cross-sectional explanatory view of a unit-size photoelectric conversion device using a conventional diode-type photoelectric conversion element. As shown in FIG. 1, a diode-type photoelectric conversion element 30 using a-Si or the like has an opaque first electrode 31 made of a metal such as Al, which also serves as a light-shielding element for directly illuminating light. Hole blocking layer 32 of Si: H or the like, a-S
i: a semiconductor layer 33 such as H, an electron blocking layer 34 such as p-type a-Si: H, and a second electrode 35 made of a transparent conductor such as ITO are sequentially laminated on a transparent substrate 1 such as glass.
It is patterned and configured.

The thin film transistor section 20 of the read switch
Are an opaque gate electrode 21 made of a metal such as Al which also serves as a shield of direct light of illumination light, an insulating layer 22 made of SiOx, SiNx or the like, a semiconductor layer 23 made of a-Si: H or the like, and an ohmic contact. A doping layer 24, a source electrode 25 made of Al or the like, and a drain electrode 26 are sequentially laminated and patterned on a transparent substrate 1 made of glass or the like.

The photoelectric conversion element 30 and the thin film transistor 20
A transparent insulating layer 2 also serving as a spacer for a document is provided thereon.
Further, a light source (not shown) for illuminating the original is arranged below the transparent substrate 1 on which these are arranged. The light 50 emitted from the light source passes through the transparent substrate 1 and the transparent insulating layer 2 and passes through the original 1
Irradiate 00. The reflected light 51 corresponding to the density of the document passes through the second electrode 35 and the electron blocking layer 34 of the photoelectric conversion element 30 and irradiates the semiconductor layer 33, so that an electron-hole pair is formed in the semiconductor layer 33. Generated, the electrons travel toward the first electrode, the holes travel toward the second electrode,
Photocurrent flows between the first and second electrodes.

The photocurrent is read out as an electric signal by using the thin film transistor 20 by, for example, a circuit as shown in FIG. 2, when the thin film transistor 20 is turned on, the potentials at both ends of the diode-type photoelectric conversion element 30 are determined to be the potential of the power supply 200 and the ground potential. That is, the internal capacitance of the photoelectric conversion element 30 is reset, and A
The potential of the point becomes the ground potential. The thin film transistor 20 is O
In the FF state, the internal capacitance is charged by the photocurrent flowing through the photoelectric conversion element 30, and the potential at the point A increases with time. The current flowing when the thin film transistor 20 is turned on again to reset the internal capacitance is again supplied to the current amplifier 2.
01, an electric signal 202 corresponding to the amount of incident light is obtained.

However, as shown in FIGS. 1 and 2, the diode-type photoelectric conversion element has a different layer structure from the thin-film transistor serving as a signal reading switch because the layer structure of the element is generally a sandwich type. After the formation, a process of forming a photoelectric conversion element is required, and the process is complicated, and there is a problem to be improved that the manufacturing cost is increased.

When a coplanar photoconductive element is used as a photoelectric conversion element, a photoelectric conversion device can be formed in the same process as a thin film transistor. However, the photoconductive element has a response to a change in light input (photoresponse). Is slow and not suitable for high-speed operation.

Another object of the present invention is to provide a high-speed and high-speed photoelectric conversion device using a photoelectric conversion element having the same configuration as a thin film transistor serving as a switch for reading out a signal in view of the above situation. It is to provide a small and inexpensive photoelectric conversion device.

In order to achieve such an object, the present invention provides:
In a photoelectric conversion device including, on the same substrate, an optical capacitance changing element whose capacitance changes by receiving light and a thin film transistor for reading a signal based on a capacitance change of the optical capacitance changing element, the optical capacitance changing element includes: A thin film transistor including a first electrode, an insulating layer, a first semiconductor layer, and a first doping layer providing a light receiving surface, wherein the thin film transistor includes a gate electrode, a gate insulating layer, a second semiconductor layer; , A second doping layer, source and drain electrodes, the insulating layer and the gate insulating layer, the first semiconductor layer and the second
Wherein the semiconductor layer, the first doping layer and the second doping layer are each formed from a common layer formed simultaneously.

The capacitance of the optical capacitance changing element changes due to light, but its response speed is sufficiently faster than that of the photoconductive light receiving element. The configuration of the optical capacitance changing element is the same as that of the thin film transistor used as the readout switch means. Since they are the same, it is possible to configure a small and inexpensive photoelectric conversion device with a fast optical response.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the present invention is to improve the light responsiveness by using a light capacitance changing element whose capacitance changes by receiving light. Will be easier to understand.

FIG. 3 is a sectional view and a top view of a photoelectric conversion element area for reading information of one pixel of the present invention. A method for manufacturing the photoelectric conversion element area of the present invention shown in FIG. 3 will be described.

(1) A lower electrode 2 of a MIS capacitor is selectively formed on an insulating substrate 1 by using Cr, and then a hydrogenated amorphous silicon nitride film (a-SiNx: H or less silicon nitride film) to be an insulating film 3 of the MIS capacitor. ) To 1000
{6500 of hydrogenated amorphous silicon (hereinafter a-Si: H) to be the thin film semiconductor 4} and 500 of the n ⁺ layer 5
順次 Deposit sequentially by plasma CVD.

(2) Aluminum, which will be the source and drain electrodes 6 and 7 later, is deposited by a 10000 ° sputtering method and then formed into a pattern of the source and drain electrodes.

(3) Next, after patterning the photosensitive resist into a desired pattern, the n ⁺ layer between the source and drain electrodes of the photoconductive element is subjected to RI using the photosensitive resist as a mask.
Etching and removal by E.

(4) After patterning with a photosensitive resist into a desired pattern, element separation is performed by RIE.

(5) A protective layer (not shown) of a silicon nitride film is formed on the surface of the thin film semiconductor formed in the above step (4) by a plasma CVD method, and is further patterned into a desired pattern by a photosensitive resist. The wire bonding pad of each electrode is exposed.

(6) Under N ₂ environment, 80 ° C. for 30 minutes, 150
Annealing is performed in steps of 30 ° C. for 30 minutes and 200 ° C. for 120 minutes, and gradually cooled to room temperature over 12 hours.

(7) Wire bonding is performed on each of the pads exposed in the step (5), and a power supply and a current amplifier IC are connected to the photoelectric conversion element area formed as described above.

As described above, the photoelectric conversion element area according to the first embodiment of the present invention is manufactured.

In order to clarify the effects of the present invention, the photoconductive element (A) and the MIS type optical capacitance change element (B) are formed as single bit elements on the same substrate by the above-described steps. Its properties were measured.

FIG. 4 shows the photoconductive element (A) and the MIS
It is a change of an output current with respect to a change of incident light of each single bit element of the type optical capacitance changing element (B). The optical capacitance change element
When the light is turned on, a current flows and stops flowing with a certain time constant. When the light is turned off, a negative current flows and stops flowing with a certain time constant. Light is ON for photoconductive element
At that moment, almost only the dark current flows, and it goes to a steady value of the photocurrent with a certain time constant. When the light is turned off, it goes from a steady value of the photocurrent to a dark current with a certain time constant.
That is, the two have a complementary relationship in terms of photoresponse, and when currents of both are added, a photoelectric conversion element that achieves both a steady value of photocurrent having a gain of a photoconductive element and a fast photoresponse of a photocapacitance element. Areas can be realized.

FIG. 3 shows the photoconductive element used in FIG.
FIG. 5 is a cross-sectional view and a top view of the photoelectric conversion area of the present invention in which the MIS type optical capacitance changing elements are internally connected in parallel, FIG. 5 is an equivalent circuit diagram including an external power supply and an ammeter, and FIG. is there. It is shown that the optical capacitance element contributes to the improvement of the optical response.

FIGS. 7 (a) and 7 (b) show the optical response of the photoelectric conversion area when the area ratio of the photoelectric conversion area is divided between the photoconductive element and the photo-capacitance changing element. is there. As the area of the photoconductive element is reduced and the area of the photocapacitance change element is increased, the steady-state value of the photocurrent that can be extracted decreases, but the differential component with respect to the change in incident light increases, resulting in an apparent optical response. Is getting better. As described above, by relatively reducing the area of the photoconductive element and increasing the area of the optical capacitance changing element in the area of a certain photoelectric conversion element area, the area shown in FIG.
One having the optical response characteristic as shown in (c) could be obtained.

FIG. 8 shows the dependence of the photoelectric conversion element obtained in FIG. 7C on the amount of light. The optical response waveform does not change with the incident light of 200 lux or the incident light of 20 lux, indicating that the present invention can be used as a photoelectric conversion area having a fast response, such as for image reading. As described above, by connecting a current amplifier, a current waveform having excellent optical response can be converted into a voltage. Therefore, it is necessary to connect a current amplifier in a one-to-one manner by arranging a plurality of photoelectric conversion element areas according to the present invention. Therefore, it goes without saying that an image reading apparatus with a high response speed can be realized.

Conventionally, there has been no idea of a photoelectric conversion element area in which a plurality of types of photoelectric conversion elements are combined to read one piece of pixel information. The present invention makes use of the characteristics of the photoconductive type, which constantly outputs a photocurrent with a gain to light, and compensates for the shortcomings of the optical response by using an optical capacitance change element. Also, the compatibility with the signal processing unit is not impaired at all.

Second Embodiment A second embodiment of the present invention relates to a one-dimensional sensor array.
The photoelectric conversion area is formed by using the photoelectric conversion area formed in the process of the first embodiment, and the driving circuit including the MIS capacitor for storing signal charges, the thin film transistor, and the like formed in the same process. FIG. 9 shows an example of the circuit of this embodiment. Here, a case of a sensor array having nine photoelectric conversion areas will be described.

As in the first embodiment, the photoelectric conversion areas S11 to S33 are provided with both the photoconductive conversion element of the present invention and the light capacity change element.

In the figure, photoelectric conversion areas S11 to S11
Reference numeral 33 denotes one block composed of three components, and a photoelectric conversion area array composed of three blocks. Photoelectric conversion area S1
Storage capacitances CS1 to CS3 respectively corresponding to S1 to S33
3. The same applies to the switching transistors T11 to T33.

The individual electrodes having the same order in each block of the photoelectric conversion areas S11 to S33 are connected to the common line 10 via the switching transistors T11 to T33, respectively.
1 to 103.

Next, the operation of the photoelectric conversion unit having such a configuration will be described with reference to a timing chart shown in FIG.

First, when light enters the photoelectric conversion areas S11 to S33, electric charges are accumulated in the capacitors CS11 to CS33 from the power supply 105 according to the intensity.

The first of the shift registers 201
, A high level is output from the parallel terminals, and the switching transistors T11 to T13 are turned on.

Switching transistors T11 to T13
Are turned on, the capacitors CS11 to CS1
3 are stored in the capacitor CL1.
To CL3.

Subsequently, the high level output from the shift register 203 shifts, and the switching transistors TS1 to TS3 are sequentially turned on.

Thus, the capacitors CL1 to CL3
The optical information of the first block transferred and stored in the
04 sequentially read out. When the information of the first block is read, a high level is applied to the terminal 104,
The switching transistors RS1 to RS3 are simultaneously turned on.

By this operation, the capacitors CL1 to CL
3 are completely discharged. Capacitor CL1
When the residual charge of CL3 is completely discharged, the shift register 201 shifts, and a high level is output from the second parallel terminal. As a result, the switching transistors T21 to T23 are turned on, and the charges accumulated in the capacitors CS21 to CS23 of the second block are transferred to the capacitors CL1 to CL3. At the same time, a high level is output from the first parallel terminal of the shift register 202, and the switching transistors R11 to R13
Is turned on, and the residual charges of the capacitors CS11 to CS13 are completely discharged.

As described above, the first block capacitor C
The discharging operation of S11 to CS13 and the transfer operation of transferring the charges accumulated in the capacitors CS21 to CS23 of the second block to the capacitors CL1 to CL3 are performed in parallel. As in the case of the first block, the switching of the shift resist 203 causes the switching transistors TS1 to TS3 to be sequentially turned on, and the capacitor C
The optical information of the second block stored in L1 to CL3 is sequentially read.

Similarly, in the case of the third block, the capacitors CS21 to CS2 of the second block are simultaneously executed in parallel with the transfer operation.
The discharging operation of No. 3 is performed, and thereafter, the above operation is repeated for each block.

Further, the signal of a specific photoelectric conversion element will be described in detail.

FIG. 11 is an equivalent circuit of an arbitrary photoelectric conversion element area and its signal processing section according to the present embodiment. In the figure, a photoelectric conversion element area 10 is connected in series with a power supply 200 and a first capacitance element 70 that does not cause a change in capacitance, and a second capacitance element 80 that does not cause a change in capacitance at a connection with the first capacitance element. The thin film transistor 20 is provided as a switch means for connecting. The switch 90 resets the potential of the second capacitor 80. Such a photoelectric conversion device can be formed in exactly the same manner as the cross-sectional view shown in FIG.

Next, the operation of the read circuit shown in FIG. 11 will be described. The capacitance values of the first and second capacitance elements are respectively represented by C
A, CB, and the potential of the power supply 200 are VA.

First, when the switch 90 is turned on, the capacitance element 80 is reset to the reset potential VB.

At a certain time, the thin film transistor 20
Is turned on, the potentials at points B and C become equal.
This potential is assumed to be V1. Light capacity change element 1 at this time
The capacitance value of 0 is defined as C1. Thin film transistor 20 is OF
Since there is no charge transfer even in the F state, points B and C
The potential at the point holds V1. That is, the charge Q1 on the left side of the thin film transistor 20 is Q1 = C1 · (V1−VA) + CA · V1. The charge Q2 on the right side is Q2 = CB · V1.

The period from the above time to the next time is a charge accumulation time. The amount of light incident on the optical capacitance changing element 9 changes, and the capacitance changes in response to C2 = C1 + ΔC with good response. Even if the light capacity change element changes, the charge amount does not change. On the other hand, the photoconductive element 8 accumulates a photocurrent or a dark current in the first capacitive element 70 to store the charge Qp.

[0051]

[Outside 1]

Then, again, the thin film transistor 20
In the N state, since the potential at point B has changed, a potential difference occurs from point C, and a current flows. After the potentials at points B and C eventually become equal at V2, the thin film transistor 20
In the FF state, the signal charge has been transferred to the second capacitor 80.

Since the charge does not move even when the thin film transistor 20 is turned off, the potentials at the points B and C are V
Holding 2.

That is, the charge Q1 'on the left side of the thin film transistor 20 is Q1' = C2２ (V2-VA) + CA ・ V2. The charge Q2 'on the right side is Q2' = CB ・ V2. From the relation of charge conservation, Q1 + Q2 + QP = Q1 ′ + Q2′∴Q2′−Q2 = Qp + ΔC · (VA−V1) − (C1
+ CA + ΔC) (V2-V1) Since the left side is CB (V2-V1),

[0055]

[Outside 2]

The left side shows the amount of change from the initial potential V1.
This is exactly the signal read to the second capacitor. The first term of the molecule on the right side is the amount of charge of the photocurrent from the photoconductive element,
The second term is a displacement current term due to a capacitance change ΔC of the optical capacitance changing element. The fact that both terms can be processed in the form of a sum
It is shown that the effect of the embodiment can be obtained also in this embodiment.

As described above, the optical capacitance changing element is connected in series to the power supply and the first capacitance element having no capacitance change, and the second capacitance having no capacitance change at the connection with the first capacitance element. By adopting a configuration in which a thin film transistor is provided as a switch means for connecting the elements, a capacitance change can be detected as a voltage output with a simple configuration without using an expensive current amplifier,
A cheaper photoelectric conversion device can be provided. Here, the first capacitance element that does not cause a capacitance change is connected in series to the optical capacitance change element. However, if the second capacitance element is provided without providing the first capacitance element, It goes without saying that a change in capacitance of the optical capacitance element can be detected by voltage.

The change in the light irradiation detected in this manner can be converted into document information by using a processing circuit as shown in FIG. 9 as in the first embodiment.

Hereinafter, another embodiment of the present invention will be described in detail.

(Third Embodiment) FIG. 12 is an explanatory sectional view of a photoelectric conversion device according to this embodiment.

Light capacity change element 10 as photoelectric conversion element
Is an opaque first electrode 11 made of a metal such as Al which also serves as a shield of direct light of illumination light, an insulating layer 12 made of SiOx, SiNx or the like, a semiconductor layer 13 made of a-Si: H or the like, and ohmic contact. Layer 14 and a second electrode 15 made of a transparent conductor such as ITO are sequentially laminated and patterned on a transparent substrate 1 such as glass.

The thin film transistor section 20 of the read switch
Is an opaque gate electrode 2 made of a metal such as Al, which also serves as a shield for direct illumination light as in the case of the optical capacitance changing element 10.
1, insulating layer 22 made of SiOx, SiNx, etc., a-S
i: A semiconductor layer 23 of H or the like, a doping layer 24 for making ohmic contact, and a source electrode 25 and a drain electrode 26 of Al or the like are sequentially laminated and patterned on a transparent substrate 1 such as glass.

In FIG. 12, the portions having the same configuration of the optical capacitance changing element 10 and the thin film transistor section 20, that is, the first electrode 11 and the gate electrode 21, the insulating layer 12 and the insulating layer 2
2. Since the semiconductor layers 13 and 23 and the doping layers 14 and 24 have the same layer structure, they are formed simultaneously.

Further, the transparent insulating layer 2 serving also as a spacer for the original is formed on the light capacity changing element 10 and the thin film transistor 20.
Is provided. Further, a light source (not shown) for illuminating the original is arranged below the transparent substrate 1 on which these are arranged. Light 50 emitted from the light source irradiates the original 100 through the transparent substrate 1 and the transparent insulating layer 2. The reflected light 51 corresponding to the density of the document passes through the second electrode 15 of the optical capacitance changing element 10 and irradiates the semiconductor layer 13 so that the first and second light beams are irradiated.
The capacitance between the electrodes changes.

It should be noted that here, the second
Although a transparent electrode was used as the electrode 15 of the
Only 4 can sufficiently function as an electrode, and a large output can be obtained without the attenuation of incident light by the transparent electrode.

The photo-capacitance change element 10 generates electron hole pairs by the irradiated light, and the doping layer is n
In the case of the mold, holes are accumulated in the semiconductor layer, and the result appears as a capacitance change. This capacitance change is generally much faster than the optical response of a photoconductive photoelectric conversion element, and has a good linearity with respect to the amount of light and can be used as a photoelectric conversion element.

This change in capacitance can be read out as an electric signal using the thin film transistor 20 by, for example, a circuit as shown in FIG. The reading method will be described with reference to the timing charts of FIGS. FIG.
(A) shows the incident light amount, (b) shows the capacitance value of the optical capacitance conversion element 10, (c) shows the ON timing of the thin film transistor 20, and (d) shows the output signal of the current amplifier 201.

First, at time t1, assuming that the capacitance value of the light capacity conversion element 10 is C1, when the thin film transistor 20 is turned on, the potentials at both ends of the light capacity conversion element 10 are determined to the potential of the power supply 200 and the ground potential. . That is,
The capacitance of the optical capacitance conversion element 10 is reset, and the potential at the point A becomes the ground potential. At this time, assuming that the potential of the power supply 200 is VA, the charge of C1 · VA has been accumulated in the optical capacitance conversion element 10. During the period when the thin film transistor 20 is in the OFF state, unlike the conventional diode type,
Since no photocurrent flows, the charge amount charged in the optical capacitance conversion element 10 does not change. At time t2, the amount of light incident on the optical capacitance conversion element 10 changes and the capacitance value becomes C2 = C1 + ΔC
Changes responsively. At this time, the charge amount does not change, but A
The potential at the point changes by VA · C1 / C2-VA. At time t3, when the thin film transistor 20 is turned on again, the potential at point A has changed, and a current flows to compensate for the change. By detecting this current with the current amplifier 201, an electric signal 202 corresponding to the amount of incident light is obtained.

As described above, according to the circuit shown in FIG. 13, the amount of incident light changes between the ON state and the ON state of the thin film transistor 20, and when the capacitance value of the optical capacitance conversion element 10 changes, the change amount Can be detected.
In other words, when the incident light amount does not change, no current flows even when the thin film transistor 20 is turned on. That is, a differential output of the incident light amount with respect to time is obtained.

FIG. 15 is a block diagram showing an example of a method for obtaining document information based on the differential output. In FIG. 15, a memory 60 stores a reference signal level, for example, an output level when a document changes from reference black to reference white. The adder 61 adds the differential output 202 of the next readout obtained by the photoelectric conversion device and the content of the memory 60.
The signal 203 resulting from this addition becomes document information. The signal 203 is stored again in the memory 60, and is added to the differential output 202 of the next reading.

Fourth Embodiment FIG. 16 is an equivalent circuit of a photoelectric conversion device according to a fourth embodiment of the present invention.

In FIG. 16, the optical capacitance conversion element 10 is connected in series with the power supply 200 and the first capacitance element 70 in which the capacitance does not change, and the second part in which the capacitance does not change in the connection with the first capacitance element. The thin film transistor 20 is provided as a switch for connecting the capacitor 80. The switch 90 resets the potential of the second capacitor 80 to the potential of the power supply 300. Such a photoelectric conversion device can be formed in exactly the same manner as the cross-sectional view shown in FIG.

Next, the operation of the read circuit shown in FIG. 16 will be described. The capacitance values of the first and second capacitance elements are respectively represented by C
A, CB, and the potential of the power supply 200 are VA.

First, when the switch 90 is turned on, the capacitance element 80 is reset to the reset potential VB.

Next, when the thin film transistor 20 is turned on, the potentials at points B and C become equal. This potential is assumed to be V1. The capacitance value of the optical capacitance conversion element 10 at this time is defined as C1. Even if the thin film transistor 20 is turned off, there is no movement of electric charge, so that the potentials at points B and C are V
Holds 1. That is, the charge Q1 on the left side of the thin film transistor 20 is Q1 = (C1 + CA) .V1-C1.VA The charge Q2 on the right side is Q2 = CB.V1.

The amount of light incident on the optical capacitance changing element 10 changes, and the capacitance changes in response to C2 = C1 + ΔC with good response. Even if the capacitance value changes, the charge amount does not change, but the potential at point B is V2 = (C1 + CA) · V1 / (C2 + CA) + Δ
C · VA / (C2 + CA).

Then, again, the thin film transistor 20
In the N state, since the potential at point B has changed to V2, a potential difference occurs from point C, and a current flows. This gives B
The potential at points C and C is V3 = (C1 + CA + CB) · V1 / (C2 + CA + C
B) + ΔC · VA / (C2 + CA + CB)

At this time, if (C1 + CA + CB) ≫ΔC is set, the first term in the above equation becomes V1, which is equal to the initial potential at points B and C. The second term is the amount of change from the initial potential V1, and is proportional to the capacitance change ΔC. That is, the capacitance change ΔC of the optical capacitance changing element can be detected as a voltage output.

As described above, according to the circuit shown in FIG. 16, the amount of incident light changes between the ON state and the ON state of the thin film transistor 20, and when the capacitance value of the optical capacitance changing element 10 changes, the change amount Can be detected as a voltage output.

FIG. 17 shows an example in which an optical sensor array is configured using the circuit shown in FIG. However, here, a case of an optical sensor array having nine photoelectric conversion elements will be described as an example.

In the figure, the optical capacitance changing elements S11 to S
Reference numeral 33 denotes one block composed of three components, and an optical sensor array composed of three blocks. Optical capacitance changing elements S11 to S
The same applies to the capacitors CS11 to CS33 and the switching transistors T11 to T33 respectively corresponding to 33.

The individual electrodes having the same order in each block of the optical capacitance changing elements S11 to S33 are connected to the common line 10 via the switching transistors T11 to T33, respectively.
1 to 103.

More specifically, the first switching transistors T11, T21, T31 of each block are connected to the common line 1
01 is the second switching transistor T of each block.
12, T22, T32 are connected to the common line 102, and the third switching transistors T13, T2 of each block.
3, T33 are connected to the common line 103, respectively (such a connection is called a matrix connection).

Switching transistors T11 to T33
Are commonly connected for each block, and connected to the parallel output terminal of the shift register 401 for each block. Therefore, the switching transistors T11 to T11 are switched according to the shift timing of the shift register 401.
Reference numeral 33 sequentially turns on for each block. Common line 101
To 103 are switching transistors TS1 to TS
It is connected to the amplifier 404 via S3.

In FIG. 17, common lines 101 to 10
3 are installed via load capacitors CL1 to CL3, respectively, and are grounded via switching transistors RS1 to RS3.

The capacity of the load capacitors CL1 to CL3 is set to be sufficiently larger than that of the storage capacitors CS11 to CS33. The gate electrodes of the switching transistors RS1 to RS3 are commonly connected, and are connected to the terminal 104. That is, when a high level is applied to the terminal 104, the switching transistors RS1 to RS3 are simultaneously turned on, and the common lines 101 to 103 are grounded.

It goes without saying that the sensor array of FIG. 17 operates in the same manner as in FIG.

As described above, the optical capacitance changing element is connected in series to the power supply and the first capacitance element having no capacitance change, and the second capacitance having no capacitance change at the connection with the first capacitance element. With a structure in which a thin film transistor is provided as a switch for connecting elements, a change in capacitance can be detected as a voltage output with a simple structure without using a current amplifier, so that a less expensive photoelectric conversion device can be provided. Here,
The first capacitance element that does not cause a capacitance change is connected in series to the optical capacitance change element. However, if the second capacitance element is provided without providing the first capacitance element, the capacitance of the optical capacitance element can be increased. Needless to say, the change can be detected by voltage.

The change in the light irradiation detected in this manner can be converted into document information by using a processing circuit as shown in FIG. 15, as in the third embodiment.

Performing the read operation by moving the charge using the thin film transistor connected to the photo-capacitance change element described above is equivalent to resetting the charge of the capacitance of the photo-capacitance change element together with the read operation. By this reset operation, the optical capacitance element could be used as a photoelectric conversion element.

When the light source illuminating the original is turned off after the reading operation and the reading operation, that is, the resetting operation is performed again, the light capacity changing element resets both the light and the bias potential. Operation can be performed.
Next, by turning on the light source again and performing the reading operation,
It is possible to obtain the information of the original at the time of the reading operation without using the circuit as shown in FIG.

[0092]

As described above, the capacitance of the above-mentioned photo-capacitance change element is changed by light, but its response speed is sufficiently faster than that of the photoconductive type photo-detection element. Since the thin film transistor is the same as the thin film transistor used as the switch means, it is possible to configure a small and inexpensive photoelectric conversion device with a fast optical response.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a conventional photoelectric conversion device.

FIG. 2 is an equivalent circuit diagram of a conventional photoelectric conversion device.

FIG. 3 is a schematic diagram for explaining an embodiment of a photoelectric conversion device according to the present invention.

FIG. 4 is a graph showing a change in output current with respect to a change in incident light of each single bit element of the photoconductive element (A) and the MIS type optical capacitance changing element (B).

FIG. 5 is an equivalent circuit diagram of an embodiment of the present invention.

FIG. 6 is a graph showing light response characteristics according to an embodiment of the present invention.

FIG. 7 is a graph showing the optical response of the photoelectric conversion element area when the area ratio of dividing the area of the photoelectric conversion area between the photoconductive element and the optical capacitance changing element is changed.

8 is a graph showing the light amount dependency of a photoelectric conversion element area according to a response (C) in FIG. 7;

FIG. 9 is a circuit configuration diagram according to an embodiment of the present invention.

FIG. 10 is a timing chart for explaining a driving method according to an embodiment of the present invention.

FIG. 11 is an equivalent circuit diagram of a certain photoelectric conversion element.

FIG. 12 is a schematic diagram for explaining another embodiment of the photoelectric conversion device of the present invention.

FIG. 13 is a circuit diagram of another embodiment of the present invention.

FIG. 14 is a timing chart for explaining a driving method according to another embodiment of the present invention.

FIG. 15 is a block diagram illustrating an example of an information processing apparatus that obtains document information based on a differential output.

FIG. 16 is an equivalent circuit diagram of a photoelectric conversion device according to another embodiment of the present invention.

FIG. 17 is a circuit configuration diagram of a photoelectric conversion device according to another embodiment of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-7659 (JP, A) JP-A-62-145866 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/146 H01L 31/10 H04N 1/028 H04N 5/335

Claims (9)

(57) [Claims] 1. A pixel for converting optical information into electrical information, a photoconductive element whose conductivity changes when receiving light, and an optical capacitance changing element whose capacitance changes when receiving light. A photoelectric conversion device comprising: one electrode of the photoconductive element and one electrode of the photocapacitance variable element are short-circuited; the other electrode of the photoconductive element and the other of the photocapacitance variable element And a light receiving surface of the photoconductive element and a light receiving surface of the optical capacitance changing element are independently juxtaposed. 2. The photoelectric conversion device according to claim 1, wherein the light capacity change element has an insulating layer and a semiconductor layer between the one electrode and the other electrode. 3. The photoconductive type device and the photocapacitance change device have the same semiconductor layer.
3. The photoelectric conversion device according to claim 1. 4. The photoelectric conversion device according to claim 3, wherein said semiconductor layer is mainly composed of an amorphous material. 5. A photoelectric conversion device, comprising: a light-capacitance change element whose capacitance changes by receiving light; and a thin-film transistor for reading a signal based on a change in capacitance of the light-capacity change element on the same substrate. The capacitance change element includes a first electrode, an insulating layer, a first semiconductor layer, and a first doping layer that provides a light receiving surface. The thin film transistor has a gate electrode, a gate insulating layer, A second semiconductor layer, a second doping layer, a source and a drain electrode, the insulating layer and the gate insulating layer, the first semiconductor layer and the second semiconductor layer, the first doping. The photoelectric conversion device, wherein the layer and the second doping layer are each formed from a common layer formed simultaneously. 6. The photoelectric conversion device according to claim 5, further comprising reset means for resetting a potential of said optical capacitance changing element to a predetermined potential in synchronization with a read operation. 7. The photoelectric conversion device according to claim 5, wherein the optical capacitance change element has a transparent electrode formed on the first doping layer. 8. An information processing apparatus comprising: the photoelectric conversion device according to claim 1; and document holding means for holding a document holding image information at a position read by the photoelectric conversion device. 9. An information processing apparatus comprising: the photoelectric conversion device according to claim 5; and document holding means for holding a document holding image information at a position read by the photoelectric conversion device.