JPH0590557A - Photoelectric converter and data processor - Google Patents

Abstract

PURPOSE:To enable the title photoelectric converter making a rapid photo- response to be manufactured by a method wherein a photoelectric conversion element area reading-out an optical data for one pixel is provided with a photoconductive element and a photo-capacity changing element changing the photocapacity by photoirradiating step. CONSTITUTION:A lower electrode 2 is formed below an insulating substrate and then an insulating film 3, a thin film semiconductor 4, an <n+> layer 5 are successively deposited on the insulating substrate. Next, after depositing aluminum, the patterns of source, drain electrodes are formed and after patterning a sensitive resist, the n<+> layer 5 between the source and drain electrodes of a photoconductive element is etched away. Furthermore, after patterning the sensitive resist, elements are separated, a protective layer is formed on the surface of a formed thin film semiconductor and after patterning the sensitive resist, wirebonding pads of respective electrodes are exposed. Finally, the photoelectric conversion element area inner-connecting the photoconductive element and photocapacity changing element in parallel with each other can be formed by connecting said elements to power supply and a current amplifier after performing the annealing and wire-bonding steps.

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 popularization of so-called electronic office machines such as facsimiles and digital copying machines, there is an increasing demand for a compact and low-cost image reading apparatus. Therefore, an image reading apparatus of the same size that can directly contact the original held by the original holding means for holding the original at the reading position and does not require an imaging system or has a short optical path length of the imaging system. Is getting attention. A typical photoelectric conversion unit used in such an image reading device is a CCD, but a photoelectric conversion unit made of a non-single-crystal semiconductor typified by amorphous silicon or CdS has a low cost and a large area. Development is actively carried out with the main feature being that it can be built.

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

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

In order to solve such a problem, one aspect of the present invention is that a photoelectric conversion element area for reading one pixel of optical information has a photoconductive type element and an optical capacitance changing element whose capacity is changed by irradiation of light. Both are provided.

According to the present invention, the optical capacitance changing element whose capacitance changes according to the amount of incident light outputs differentially the charge with respect to the change in the amount of incident light, and the output of the photoconductive type element having a slow photoresponse. It is possible to form a photoelectric conversion part having a high photoresponse by acting so as to compensate each other with a charge current generated by the photoresponse.

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 unity-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 and an n-type a- which also serves to shield direct light of illumination light. Si: H or the like hole blocking layer 32, a-Si:
A semiconductor layer 33 made of H or the like, an electron blocking layer 34 made of p-type a-Si: H and a second electrode 35 made of a transparent conductor such as ITO are sequentially laminated and patterned on the transparent substrate 1 made of glass or the like. ..

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

Photoelectric conversion element 30 and thin film transistor 20
A transparent insulating layer 2 which also serves as a spacer for the original is provided on the top.
Further, a light source (not shown) for illuminating the document 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 the original 1
Irradiate 00. The reflected light 51 according to the light and shade of the original is transmitted through the second electrode 35 of the photoelectric conversion element 30 and the electron blocking layer 34, and is irradiated to the semiconductor layer 33, so that electron-hole pairs are formed in the semiconductor layer 33. The generated electrons travel toward the first electrode and the holes travel toward the second electrode,
A photocurrent flows between the first and second electrodes.

This photocurrent is read out as an electric signal using the thin film transistor 20 in a circuit as shown in FIG. 2, for example. 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 at 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 rises with time. Again, when the thin film transistor 20 is turned on and the internal capacitance is reset, the current flowing through the current amplifier 2
By detecting with 01, the electric signal 202 according to the amount of incident light is obtained.

However, as shown in FIGS. 1 and 2, the diode-type photoelectric conversion element has a layer structure of a sandwich type, which is different from that of a thin film transistor which serves as a signal reading switch. After forming the film, a process for forming a photoelectric conversion element is required, which complicates the process and raises the manufacturing cost, which is a problem to be improved.

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

Another object of the present invention is, in view of such a situation, a high optical response and a high speed using a photoelectric conversion element having a structure similar to that of a thin film transistor which serves as a switch means for signal reading. An object is to provide a small-sized and inexpensive photoelectric conversion device.

In order to solve the above problems, according to the present invention, an optical capacitance changing element whose capacitance changes by irradiation of light and a thin film transistor for reading the capacitance change of the optical capacitance changing element are formed on the same insulating substrate. In the photoelectric conversion device, the optical capacitance changing element has a MIS structure including a first electrode, an insulating layer, a semiconductor layer, and a second electrode forming an ohmic junction with the semiconductor layer, and the thin film transistor is A gate electrode, an insulating layer, a semiconductor layer, a source and a drain electrode forming an ohmic junction with the semiconductor layer, and at least the insulating layer and the semiconductor layer forming the thin film transistor and the optical capacitance change element are the same. Is characterized by.

Although the capacitance of the optical capacitance changing element is changed by light, its response speed is sufficiently faster than that of a photoconductive type light receiving element, and the optical capacitance changing element has a thin film transistor used as a read switch means. Since they are the same, it is possible to configure a photoelectric conversion device that is fast, small in size, and inexpensive.

[0016]

[Embodiments] As described above, the present invention is to improve the photoresponsiveness by using the light capacitance changing element whose electrostatic capacitance changes by receiving light. The details of each of the embodiments will be described below. Will be easier to understand.

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

(1) A hydrogenated amorphous silicon nitride film (a-SiNx: H or less silicon nitride film) is formed on the insulating substrate 1 by selectively forming the lower electrode 2 of the MIS capacitor with Cr, and then becomes the insulating film 3 of the MIS capacitor. ) 1000
A, hydrogenated amorphous silicon (hereinafter a-Si: H) to be the thin film semiconductor 4 is 6500 A, and n ⁺ layer 5 is 500
They are sequentially deposited by the Ai plasma CVD method.

(2) After depositing aluminum to be source and drain electrodes 6 and 7 by a sputtering method of 10000i, it is formed into a pattern of source and drain electrodes.

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

(4) Further, after patterning a desired pattern with a photosensitive resist, element isolation is performed by RIE.

(5) A protective layer 8 of a silicon nitride film is formed on the surface of the thin film semiconductor formed in (4) by a plasma CVD method, and a desired pattern is patterned with a photosensitive resist, and then wire bonding of each electrode is performed. Expose the pad.

(6) Under N2 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 pad exposed in (5), and the power source and the current amplifier IC are connected to the photoelectric conversion element area thus formed.

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

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

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

FIG. 3 shows the photoconductive element used in FIG.
FIG. 5 shows an equivalent circuit diagram including an external power source and an ammeter, and FIG. 6 shows the obtained optical response, in which a cross section and a top view of a photoelectric conversion area of the present invention in which MIS type optical capacitance changing elements are internally connected in parallel are provided. is there. It has been shown that the optical capacitance element contributes to the improvement of the optical response.

FIGS. 7 (a) and 7 (b) show the state of the optical response of the photoelectric conversion area when the area ratio of dividing the area of the photoelectric conversion area between the photoconductive type element and the optical capacitance changing element is changed. is there. The steady-state value of the photocurrent that can be taken out decreases as the area of the photoconductive element is decreased and the area of the optical capacitance change element is increased, but the differential component with respect to the change of the incident light increases and the apparent optical response is increased. Is getting better. In this way, by actually reducing the area of the photoconductive type element and increasing the area of the optical capacitance changing element within the area of a certain photoelectric conversion element area, the area of the photoelectric conversion element is actually increased.
It was possible to obtain the one having an optical response characteristic as shown in (c).

FIG. 8 shows the light quantity dependence of the photoelectric conversion element obtained in FIG. 7 (c). The optical response waveform remains the same regardless of whether the incident light of 200 lux or the incident light of 20 lux is blocked, indicating that the present invention can be used as a photoelectric conversion area with a fast response for applications such as image reading. As described above, by connecting a current amplifier as in the present embodiment, a current waveform having an excellent optical response can be converted into a voltage. Therefore, a plurality of photoelectric conversion element areas of the present invention are arranged in a one-to-one correspondence. It goes without saying that an image reading device with a fast response can be realized by connecting a current amplifier to the.

Conventionally, there is no concept of a photoelectric conversion element area in which a plurality of types of photoelectric conversion elements are combined to read one pixel information. INDUSTRIAL APPLICABILITY The present invention makes use of the characteristics of a photoconductive type that constantly outputs a photocurrent with a gain with respect to light, while compensating for the defect of optical response by an optical capacitance change element, which is an advantage of a simple manufacturing process. However, compatibility with the signal processing unit is not impaired at all.

(Second Embodiment) In the second embodiment of the present invention, a one-dimensional sensor array is formed by the photoelectric conversion area formed in the process of the first embodiment and the same process as the photoelectric conversion area. The drive circuit is composed of a MIS type capacitor for signal charge storage, a thin film transistor and the like. FIG. 9 shows an example of the circuit of this embodiment. However, here, the case of a sensor array having nine photoelectric conversion areas will be taken up.

The photoelectric conversion areas S11 to S33 include both the photoconductive conversion element of the present invention and the optical capacitance changing element, as in the first embodiment.

In the figure, photoelectric conversion areas S11 to S
Three blocks 33 configure one block, and three blocks configure a photoelectric conversion area array. Photoelectric conversion area S1
1 to S33 respectively corresponding to storage capacities CS1 to CS3
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.
It is connected to one of 1 to 103.

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

First, when light is incident on the photoelectric conversion areas S11 to S33, electric charges are accumulated in the capacitors CS11 to CS33 from the power source 105 according to the intensity thereof.

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

Switching transistors T11 to T13
Is turned on, the capacitors CS11 to CS1
The charges accumulated in 3 are stored in the capacitor CL1 respectively.
To CL3.

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

As a result, the capacitors CL1 to CL3 are
The optical information of the first block transferred and stored in the amplifier 2
It is read sequentially through 04. 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 turned on at the same time.

By this operation, the capacitors CL1 to CL are
The residual charge of 3 is 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.

Thus, the capacitor C of the first block is
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. Then, similarly to the case of the first block, the switching resisters 203 are shifted to sequentially turn on the switching transistors TS1 to TS3, and the capacitor C
The optical information of the second block accumulated 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 parallel to the transfer operation.
3 is performed, and the above operation is repeated for each block in the same manner.

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 this embodiment. In the figure, the photoelectric conversion element area 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 capacitance element 80 in which the capacitance does not change at the connection portion with the first capacitance element. A thin film transistor 20 is provided as a switch means for connecting the two. Further, the switch 90 resets the potential of the second capacitive element 80. The structure of 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 value of each of the first and second capacitance elements is C
The potentials of A, CB, and the power supply 200 are VA.

First, at time t1, the switch 90 is turned on, so that the capacitance element 80 is reset to the reset potential V.
Reset to B.

Next, at time t2, when the thin film transistor 20 is turned on, the potentials at points B and C become equal. Let this potential be V1. The capacitance value of the optical capacitance changing element 10 at this time is C1. Even if the thin film transistor 20 is turned off, the electric charges do not move, and therefore, the potentials at the points B and C hold V1. That is, the charge Q1 on the left side of the thin film transistor 20 is Q1 = C1. (V1-VA) + CA.V1 and the charge Q2 on the right side is Q2 = CB.V1.

The charge accumulation time is from time t2 to time t3. The amount of light incident on the optical capacitance changing element 9 changes and the capacitance value changes to C2 = C1 + ΔC with good response. Even if the optical capacitance changing element changes, the charge amount does not change. On the other hand, the photoconductive type element 8 accumulates the charge Qp in the first capacitive element 70 with a photocurrent or a dark current.

[0051]

[Outer 1]

At time t4, the thin film transistor 2 is turned on again.
When 0 is in the ON state, the potential at the point B is changing, so that a potential difference is generated between the point C and the current flows. After the potentials at the points B and C become equal at V2, the thin film transistor 20 is turned off at time t5, and the signal charge is transferred to the second capacitor 80.

Even if the thin film transistor 20 is turned off, the electric charges do not move. Therefore, the potentials at the points B and C are V
Holds 2.

That is, the charge Q1 'on the left side of the thin film transistor 20 is Q1' = C2. (V2-VA) + CA.V2 and the charge Q2 'on the right side is Q2' = CB.V2. From the relation of conservation of electric charge, 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 is the amount of change from the initial potential V1,
It is exactly the signal read by the second capacitive element. The first term of the molecule on the right side is the charge amount of the photocurrent from the photoconductive element,
The second term is a displacement current term due to the capacitance change ΔC of the optical capacitance change element. The fact that both terms can be processed in the sum form
It is shown that the effect of the embodiment can be obtained in this embodiment.

As described above, the optical capacitance changing element is connected in series with the power source and the first capacitance element that does not change the capacitance, and the second capacitance that does not change the capacitance at the connection portion with the first capacitance element. By adopting a configuration in which a thin film transistor is provided as the switch means for connecting the elements, the 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 in which the capacitance does not change is connected in series to the optical capacitance change element, but if the second capacitance element is provided without providing the first capacitance element, It goes without saying that the capacitance change of the optical capacitance element can be detected by the voltage.

The change in the irradiation of the light thus detected can be converted into the information of the original by using the processing circuit as shown in FIG. 9 as in the first embodiment.

Another embodiment of the present invention will be described in detail below.

(Third Embodiment) FIG. 12 is a cross sectional view showing a photoelectric conversion device according to this embodiment.

Optical capacitance changing element 10 which is a photoelectric conversion element
Is an opaque first electrode 11 made of a metal such as Al that also serves to block direct light of illumination light, an insulating layer 12 made of SiOx, SiNx, etc., a semiconductor layer 13 made of a-Si: H, etc., and an ohmic contact is made. The doping layer 14 and the second electrode 15 made of a transparent conductor such as ITO are sequentially laminated and patterned on the transparent substrate 1 such as glass.

Thin film transistor portion 20 of the read switch
Is an opaque gate electrode 2 made of a metal such as Al that also serves to block direct light of illumination light, like the light capacity changing element 10.
1, insulating layer 22 made of SiOx, SiNx, etc., aS
A semiconductor layer 23 of i: H or the like, a doping layer 24 for making ohmic contact, and a source electrode 25 and a drain electrode 26 made of Al or the like are sequentially laminated and patterned on a transparent substrate 1 such as glass.

In FIG. 12, the portions where the optical capacitance changing element 10 and the thin film transistor section 20 have the same structure, that is, the first electrode 11 and the gate electrode 21, the insulating layer 12 and the insulating layer 2
2, the semiconductor layer 13 and the semiconductor layer 23, and the doping layer 14 and the doping layer 24 have the same layer structure, and thus are formed at the same time.

Further, the transparent insulating layer 2 which also functions as a spacer for the original is provided on the light capacity changing element 10 and the thin film transistor 20.
To provide. Further, a light source (not shown) for illuminating the document 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 illuminates the original 100. The reflected light 51 according to the lightness and darkness of the original passes through the second electrode 15 of the light capacity changing element 10 and is irradiated to the anti-conductor layer 13, so that the first and second light rays are irradiated.
The capacitance between the two electrodes changes.

In this case, the second element of the optical capacitance changing element 10 is
Although the 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 attenuation of incident light by the transparent electrode.

The light-capacitance changing element 10 is irradiated with light to generate electron hole pairs, of which 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 photoresponse of a photoconductive type photoelectric conversion element, and the linearity with respect to the amount of light is good and it can be used as a photoelectric conversion element.

This capacitance change can be read out as an electric signal by using the thin film transistor 20 in a circuit as shown in FIG. 13, for example. The reading method will be described with reference to the timing charts of FIGS. 13 and 14. 14
(A) shows the amount of incident light, (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, assuming that the capacitance value of the optical capacitance conversion element 10 is C1 at time t1, when the thin film transistor 20 is turned on, the potentials at both ends of the optical capacitance conversion element 10 are determined to be 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, if the potential of the power supply 200 is VA, it means that the electric charge C1 · VA is accumulated in the optical capacitance conversion element 10. When the thin film transistor 20 is in the OFF state, unlike the case of the diode type of the conventional example,
Since no photocurrent flows, the amount of charge charged in the optical capacity 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 is C2 = C1 + ΔC.
Change in response to. 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 the point A is changing, so a current flows to compensate for this. 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 variation amount. Can be detected.
In other words, if there is no change in the amount of incident light, no current flows even if the thin film transistor 20 is turned on. That is, a differential output of the amount of incident light with respect to time is obtained.

FIG. 15 shows a block diagram of an example of a method for obtaining information of a document based on this 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 next read differential output 202 obtained by the photoelectric conversion device and the contents of the memory 60.
The signal 203 resulting from this addition serves as the document information. The signal 203 is again stored in the memory 60 and added to the differential output 202 of the next read.

(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 capacitance in which the capacitance change does not occur in the connection portion with the first capacitance element. The thin film transistor 20 is provided as a switch means for connecting the capacitive element 80. Further, the switch 90 resets the potential of the second capacitor 80 to the potential of the power supply 300. The structure of 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 value of each of the first and second capacitance elements is C
The potentials of A, CB, and the power supply 200 are VA.

First, at time t1, the switch 90 is turned on, so that the capacitance element 80 is reset to the reset potential V.
Reset to B.

Next, at time t2, when the thin film transistor 20 is turned on, the potentials at points B and C become equal. Let this potential be V1. The capacitance value of the optical capacitance conversion element 10 at this time is C1. Even if the thin film transistor 20 is turned off, the electric charges do not move, and therefore, the potentials at the points B and C hold V1. That is, the charge Q1 on the left side of the thin film transistor 20 is Q1 = (C1 + CA) .multidot.V1-C1.VA, and the charge Q2 on the right side is Q2 = CB.V1.

At time t3, the amount of light incident on the optical capacitance changing element 10 changes, and the capacitance value changes with good response to C2 = C1 + ΔC. Even if the capacitance value changes, the charge amount does not change, but B
The potential at the point changes to V2 = (C1 + CA) · V1 / (C2 + CA) + ΔC · VA / (C2 + CA).

At time t4, the thin film transistor 2 is again turned on.
When 0 is in the ON state, the potential at the point B has changed to V2, so that a potential difference occurs with the point C and a current flows. As a result, the potentials at the points B and C are equalized by V3 = (C1 + CA + CB) .multidot.V1 / (C2 + CA + CB) +. DELTA.C.VA/(C2+CA+CB).

If (C1 + CA + CB) >> ΔC is set at this time, the first term in the above equation becomes V1, which is equal to the initial potentials 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 change element can be detected as a voltage output.

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

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

In the figure, the light capacitance changing elements S11 to S
Three blocks 33 form one block, and three blocks form an optical sensor array. Optical capacitance changing elements S11 to S
The same applies to capacitors CS11 to CS33 and switching transistors T11 to T33 respectively corresponding to 33.

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

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

Switching transistors T11 to T33
The gate electrodes of are commonly connected in each block and are connected to the parallel output terminal of the shift register 401 in each block. Therefore, depending on the shift timing of the shift register 401, the switching transistors T11 to T
33 is sequentially turned on for each block. Common line 101
103 are switching transistors TS1 to T, respectively.
It is connected to the amplifier 404 via S3.

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

The capacitances of the load capacitors CL1 to CL3 are set sufficiently larger than those of the storage capacitors CS11 to CS33. The gate electrodes of the switching transistors RS1 to RS3 are commonly connected and connected to the terminal 104. That is, when the 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 similarly to that of FIG.

As described above, the optical capacitance changing element is connected in series to the power source and the first capacitance element in which the capacitance does not change, and the second capacitance in which the capacitance change does not occur in the connection portion with the first capacitance element. Since a thin film transistor is provided as the switch means for connecting the elements, a capacitance change can be detected as a voltage output with a simple configuration without using a current amplifier, and thus a cheaper photoelectric conversion device can be provided. In addition, here
Although the first capacitance element in which the capacitance change does not occur is connected in series to the optical capacitance change element, if the second capacitance element is provided without providing the first capacitance element, the capacitance of the optical capacitance element It goes without saying that the change can be detected by voltage.

The change in the irradiation of the light thus detected can be converted into the information of the original by using the 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 light capacitance change element described above is equivalent to resetting the charge of the capacitance of the light capacitance change element together with the read operation. By this reset operation, the light capacitive element could be used as a photoelectric conversion element.

Furthermore, when the light source illuminating the original is turned off after the reading operation is completed and the reading operation, that is, the reset operation is performed again, the optical capacitance changing element is reset with respect to both light and bias potential. It can operate.
Next, by turning on the light source again and performing a read operation,
Even without using the circuit as shown in FIG. 15, the information of the original at the time of the read operation can be obtained.

[0092]

The capacitance of the optical capacitance changing element as described above changes depending on light, but its response speed is sufficiently faster than that of the photoconductive type light receiving element, and the configuration of the optical capacitance changing element is read. Since the thin film transistors used as the switch means are the same, it is possible to configure a photoelectric conversion device that is fast, small in size, and inexpensive.

[Brief description of 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 example of an embodiment of a photoelectric conversion device of 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 type 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 optical 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 photoelectric conversion area area between the photoconductive type element and the optical capacitance changing element is changed.

8 is a graph showing the light amount dependence of the photoelectric conversion element area by the response (C) in FIG.

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 one photoelectric conversion element.

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

FIG. 13 is a circuit configuration diagram of another embodiment example 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 for explaining an example of an information processing apparatus of a system that obtains document information based on 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 front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01L 31/10 H04N 1/028 A 9070-5C 7210-4M H01L 31/08 Q 8422-4M 31/10 E

Claims (9)

[Claims] 1. A pixel for converting optical information into electric information, which comprises a photoconductive type element whose conductivity changes by receiving light and an optical capacitance changing element whose capacity changes by receiving light. A photoelectric conversion device characterized by. 2. The photoelectric conversion device according to claim 1, wherein the light capacity changing element has a first electrode, an insulating layer, a semiconductor layer, and a second electrode. 3. The photoconductive element and the optical capacitance conversion element have the same semiconductor layer.
The photoelectric conversion device described in 1. 4. The photoelectric conversion device according to claim 3, wherein the semiconductor layer is mainly composed of an amorphous material. 5. A photoelectric conversion device comprising an optical capacitance change element whose capacitance changes by receiving light and a thin film transistor for reading the capacitance change of the optical capacitance change element on the same substrate. Has a first electrode, an insulating layer, a first semiconductor layer, and a second electrode, and the thin film transistor has a gate electrode, a gate insulating layer, a second semiconductor layer, and source and drain electrodes. The photoelectric conversion device is characterized in that the insulating layer and the gate insulating layer are common, and the first and second semiconductor layers are common. 6. The photoelectric conversion device according to claim 5, further comprising a reset unit that resets the potential of the light capacitance changing element to a predetermined potential in synchronization with the read operation. 7. A means for cutting off the light irradiating the optical capacitance changing element after the read operation, and a means for resetting the electric potential of the optical capacitance changing element to a predetermined electric potential while the light is being cut off. The photoelectric conversion device according to claim 5, further comprising: 8. An information processing apparatus, comprising: the photoelectric conversion device according to claim 1; and a document holding unit that holds a document carrying image information at a reading position by the photoelectric conversion device. 9. An information processing apparatus comprising: the photoelectric conversion device according to claim 5; and a document holding unit that holds a document carrying image information at a reading position by the photoelectric conversion device.