JPS63161683A - Optoelectric converter - Google Patents

Abstract

PURPOSE:To obtain a high S/N ratio which is the same as the ratio of a static operation by connecting 2nd electrode in common with 3rd electrode. CONSTITUTION:A sensor power source VS is connected to a drain electrode D and a gate electrode G is connected in common with a source electrode S. A storage capacitor C is connected to the source electrode S and further a load resistor RL is connected to the source electrode S through a transfer switch SW. When the transfer switch S is switched from ON to OFF, a photocurrent iS is applied to the capacitor C and the charging of the capacitor C is started. Along with the progress of the charging, voltage VC increases. On the other hand, as the gate electrode G is connected in common with the source electrode S, the voltage >=VGS is always zero. Therefore, a transient photocurrent is not applied when the transfer switch SW is ON.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a photoelectric conversion device used in barcode leagues, facsimile machines, digital copying equipment, etc. f provided and configured
The present invention relates to a 1i film transistor (hereinafter referred to as TPT) type photoelectric conversion device.

(Prior Art) First, as a configuration example of a TFT type optical sensor, in FIG. etc., 2 is a gate electrode,
3 is an insulating layer, 4 is a photoconductive semiconductor layer, 6 and 7 are source and drain electrodes, respectively, and 5 is an n layer for making ohmic contact with the semiconductor layer 4 and the source and drain electrodes 6 and 7.
° It is a layer.

By applying a bias voltage to the gate electrode, TFT type sensors can control the influence of the insulating layer interface and suppress dark current, so the light intensity dependent characteristic (hereinafter referred to as γ) of the photoelectric conversion output is a good characteristic close to 1. It also has the characteristics of good reproducibility and little variation within lots and between rows.

(Problems to be Solved by the Invention) These characteristics show favorable results under static (DC voltage) driving conditions, but under dynamic operation such as that normally used in image sensors, that is, charge There were problems when used in storage mode. The problems will be discussed below.

FIG. 3 shows an accumulation mode readout circuit using a TFT type sensor. A sensor power supply VS is connected to the drain electrode, and a bias power supply v8 is connected to the gate electrode.

A storage capacitor C is connected to the source electrode. The charge stored in the storage capacitor C is transferred to the transfer switch SW.
is discharged to the load resistance RL.

The operating waveforms in this circuit are shown in FIG. 4. The transfer switch SW is turned green at the same period 0N10FF for the storage time Ts. That is, when the transfer switch SW is in the OFF state, the sensor photocurrent js is charged in the storage capacitor C, and when the transfer switch SW is in the ON state, the accumulated charge in the storage capacitor C is discharged through the load resistance R and read out as an output. .

Here, if we pay attention to the voltage VC across the storage capacitor C, the voltage VC is the integral value of is, and under the condition of Vs>>Vc, VC=f is dtzis @t, and the voltage V
C increases almost linearly with respect to time t. The state of the voltage VC at this time is shown by the broken line in FIG.

However, when actually driven using the circuit shown in FIG. 3, the voltage VC had a distorted waveform as shown by the solid line in FIG. The reason for this is that when the transfer SW is turned on, the voltage VC suddenly changes to zero potential, and the gate bias potential Δv1. becomes relatively shallow, causing a transient current ia between the source and drain.
This is because (the current indicated by diagonal lines in FIG. 4) flows. Due to the influence of this transient current, the light intensity dependence of the output of the photoelectric conversion device using this circuit becomes γ = 0, as shown in Figure 5.
．． 4 to 0.5, and γ calculated from static characteristic measurements.
= 1, and the S/N ratio decreases.

The present invention solves the above-mentioned problems in dynamic operation,
An object of the present invention is to provide a photoelectric conversion device that fully utilizes the features of a TFT type sensor.

Furthermore, another object of the present invention is to propose a drive circuit that can be easily made on the same substrate as part of the sensor.
Our objective is to provide a low-cost, high-yield photoelectric conversion device by taking advantage of the high S/N ratio and reduced variation distribution, which are the characteristics of TFT sensors.

(Means for Solving the Problems) The photoelectric conversion device of the present invention includes a photoconductive layer, first and second electrodes provided facing the photoconductive layer on the same plane,
A photoelectric conversion section is configured with a third electrode provided on the photoconductive layer via an insulating layer, and a power supply voltage is applied to the first electrode to obtain a photoelectric conversion output from the second electrode. The second electrode is commonly connected to a third electrode.

In the photoelectric conversion device of the present invention, since the aforementioned transient current does not flow, it is possible to obtain a device in which γ is approximately close to 1, the S/N ratio is high, and the reproducibility is excellent. Furthermore, since the drive circuit and the photoelectric conversion section can be formed simultaneously on the same substrate, a low-cost, high-performance charging conversion device can be realized.

Examples of the present invention will be described below.

Embodiment 11 An equivalent circuit of an embodiment of a photoelectric conversion device according to the present invention is shown in FIG.

A sensor power supply Vs is connected to the drain electrode, and the gate electrode G is commonly connected to the source electrode S. Further, a storage capacitor 〇 is connected to the source electrode S, and a load resistor R1 is further connected to the source electrode S via a transfer switch SW.

Next, the operation of the photoelectric conversion device having the equivalent circuit shown in FIG. 6 will be explained.

When the transfer switch SW is switched from ON to OFF, the photoelectric current is flows into the storage capacitor 〇, and charging starts. As storage capacitor C continues to charge, voltage VC increases.

On the other hand, since the gate electrode G and the source electrode S are commonly connected, the gate-source voltage ΔV-JS is always at zero potential. Therefore, the transient photocurrent that occurs when the transfer switch SW is turned on does not flow.

[Example 2] FIG. 7 shows an equivalent circuit of a line sensor type photoelectric conversion device constructed by arranging nxm photoelectric conversion devices shown in FIG. 6 in an array.

In the figure, Sl"5nxs is a TFT type photoelectric conversion unit, CSt
``C5nxs is a storage capacitor, Ul to UnXI are reset TFTs, and T+ to TnXl are transfer TPTs.

The above element group is divided into m blocks of n elements each, m+1
It is matrix-connected to four gate lines and n signal lines. 11 is a part of the dryer for sequentially applying voltage to the gate lines VGI to VG*, l; 12 is a signal line S l
"S is a signal processing unit for extracting the signal voltage of n. Also, Vs is the sensor bias, VR is the reset voltage of the M product capacitor, and CL, l to C[. are the load capacitors.

This circuit is provided with a reset TFTU, so that after transferring the charge from the storage capacitor 〇s, the remaining charge can be completely reset. Also, reset) TFTU
The gate electrode of the block is commonly connected to the gate electrode of the transfer TFTT of the next block. By shifting the voltage pulses of the driver portion 11, the previous block can be reset at the same time as the next block's signals are transferred.

The above circuits can all be configured on the same substrate. In particular, by using a-, Si:HIIU produced by glow discharge method as a photoconductive semiconductor material, TFT-type photoelectric conversion units, storage capacitors, transfer and reset) T
PT, wiring part, etc. as lower electrode, 5iNH insulating layer, a-St:
This can be achieved by simultaneous processes using a laminated structure of the H layer, the n' layer, and the upper electrode.

The photoelectric conversion device of the present invention can be suitably applied to such a line sensor type photoelectric conversion device using the same substrate and simultaneous processes. Hereinafter, an example of a pattern of a photoelectric conversion device using this type of process will be described.

FIG. 8 shows the configuration of one bit of the circuit of FIG. 7 (turn diagram); however, to avoid complicating the diagram, only the upper and lower wiring patterns and contact hole portions are shown.

In the figure, 13 is a signal line matrix section, 14 is a photoelectric conversion section,
15 is a contact hole for connecting the gate and source, 16 is a storage capacitor, 17 is a transfer TPT, 18 is a reset TPT, and 19 is a gate drive line wiring section. still,
In this example, a so-called lens-less configuration is adopted in which an image-forming lens is not used, and the document is read by directly superimposing it on a part of the sensor. Therefore, a window 20 is provided for illuminating the original, and the lower gate electrode of a portion of the sensor is formed of an opaque material and also serves as a light shielding film. T for transfer and reset
Two PTs 17 and 18 are arranged in mirror-symmetrical positions. This is to prevent the gate-source capacitance of the TFT from changing by compensating for this pair of TPTs when the alignment accuracy of the lower electrode pattern and the upper electrode pattern changes in the longitudinal direction of the substrate. This change in the gate-source capacitance in the longitudinal direction appears as an offset component of the signal output. By using the above pattern, this offset component can be removed. Load capacitor C port (i=
1 to n) are not shown in FIG. 8, but their capacitances are relative to the stray capacitance between the signal lines S and -Sn that occurs in the signal matrix section 13.

It is set to 10 to several hundred times. Of course, it is also possible to directly read out the current in the form of a current using a load resistor, as in the embodiment described above, without using a load capacitor.

FIG. 9 shows a sectional view taken along line xx' in FIG. 8, and FIG. 10 shows a sectional view taken along line Y-Y'' in FIG.

In the figure, 1 is a substrate made of glass or the like, 21 is a lower electrode, which is a gate electrode of a part of the sensor in FIG. 9, and a gate electrode of a TPT in FIG. 1O.

Reference numeral 3 denotes an insulating layer made of SiNxH, Si02, or the like.

4 is a photoconductive semiconductor layer formed of α-3i:H or the like.

5 is an n layer for making ohmic contact with the upper electrode; 22
．． 23 is the upper electrode, which in Fig. 9 is the source electrode of a part of the sensor;
In FIG. 10, these are the source and drain electrodes of TPT.

(Effects of the Invention) As explained above, according to the present invention, both the gate and source electrodes of the TFT type photoelectric conversion device are commonly connected, so that (1) a transient photocurrent flows during the current accumulation operation; Therefore, γ=1, and the same high S/N ratio as in static operation can be obtained.

(2) Part of TFT type sensor, TP for transfer and reset
Since the T, storage capacitor, etc. can all be fabricated on the same substrate in a simultaneous process, a line sensor type photoelectric conversion device with a high S/N ratio and low cost can be provided.

There are other effects.

[Brief explanation of the drawing]

FIG. 1 is an enlarged plan view of a part of a sensor in a conventional photoelectric conversion device, and FIG. 2 is a sectional view taken along the line x-x' in FIG.
FIG. 3 is an equivalent circuit of a conventional photoelectric conversion device, FIG. 4 is an operation timing diagram, FIG. 5 is a characteristic diagram, FIG. 6 is an equivalent circuit diagram of an embodiment of the present invention, and FIG. An equivalent circuit diagram of another embodiment of the invention, FIG. 8 is a partially enlarged pattern diagram, and FIGS. 9 and 9 are cross-sectional views taken along the line x-x' in FIG.
FIG. 1θ is a sectional view taken along the line YY' in FIG. l...Substrate 2...Gate electrode 3...Insulating layer 4...Semiconductor layer 5...N layer 6.7.21.22.23...Electrode Figure 1 Figure 2 ■ Third diagram. Figure 4 'VGS ---' -V9 Figure 5 1og Voke Figure 6 Figure 8 Figure 9 Figure 10 Country

Claims (1)

[Claims] 1. A photoconductive layer, first and second electrodes provided oppositely on the same plane as the photoconductive layer, and a third electrode provided on the photoconductive layer via an insulating layer. In a photoelectric conversion device comprising a photoelectric conversion section, applying a power supply voltage to the first electrode and obtaining a photoelectric conversion output from the second electrode, the second electrode is commonly connected to a third electrode. A photoelectric conversion device characterized by: