JPH0379910B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a contact type image sensor used in a sensor section of a document reading device such as a facsimile machine and a method for driving the same, in order to reduce the size and cost of a document reading device such as a facsimile.

In recent years, in document reading devices such as facsimiles,
One-on-one with the original surface for the purpose of miniaturization and lower cost.
The development of contact-type image sensors, which can reduce the size of the optical system in response to the current situation, is gaining momentum. Several types of image sensors have been devised as a method for realizing this, but these image sensors are broadly classified into storage type and non-storage type in terms of driving method. The former accumulates charges generated by light during one line scanning time in a photoelectric exchange element such as a photodiode, and reads this. Because the charges are accumulated, the signal ratio between dark and bright is large, and the photoresponse is particularly sensitive. has the advantage of being fast. At present, methods using a Saticon film or an amorphous silicon film have been announced. The latter does not accumulate charge and simply uses its properties as a photoconductor to detect the intensity of light reflected on the document surface as a change in the resistance of the sensor element. It has the disadvantage of slow response.

However, when it comes to driving the sensor,
Currently, storage-type image sensors have a major drawback in that they require dedicated ICs with shift register and analog switch array functions.
On the other hand, non-storage type image sensors can be driven in a matrix type by providing a rectifying contact on one of the electrodes, requiring only a small number of switches and no dedicated IC, which is extremely cost-effective. advantageous to One possible way to solve the drawbacks of this storage type image sensor is to configure the part corresponding to this IC with thin film transistors built on the same substrate, but this is currently not possible due to two reasons. So far, there have been no published examples of this application. One is that the mobility of thin film transistors is generally much lower than that of transistors made of single crystals, and their response speed is slow, making it impossible to perform high-speed switching. The other problem is that it is difficult to manufacture thin film transistors uniformly and integratedly over a large area with good reproducibility. Another secondary reason is that if a relatively high-speed thin film transistor array and a contact image sensor array are made on the same substrate, the process becomes extremely complicated.

The object of the present invention has been made in view of the above-mentioned circumstances.
The object of the present invention is to provide a high-speed solid-state photoelectric conversion device that does not require an IC.

According to the present invention, when an accumulation type image sensor array and a thin film transistor array are configured as a pair on a substrate, and the thin film transistor array is divided into several blocks and the blocks are scanned, the thin film transistors in one block are turned on at the same time. , the charge of the storage image sensor element corresponding to that block is simultaneously detected as a signal by the same number of detection circuits as the number of sensor elements in the block, for example, consisting of capacitors, integrators, etc., and then sent to a high-speed switch. As a result, a solid-state photoelectric conversion device is obtained, which is characterized in that the signal is read out by scanning the solid-state photoelectric conversion device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles and effects of the contact type image sensor and its driving method of the present invention will be explained below while illustrating the basic configuration and some embodiments of the present invention.

FIGS. 1a and 1b show the basic structure of a contact type image sensor of the present invention. In Figure 1a, 1 is
(1) to (n) are block drive circuits that sequentially switch each block; 2 indicates one block of an accumulation type image sensor array and a thin film transistor array;
As shown in Figure b. As shown in the figure, one block consists of m pairs of sensor elements and transistor elements, and since there are n blocks, the total number of bits is n×m. Reference numeral 3 denotes a reading circuit including m detection circuits, a scanning circuit for scanning them, and, if necessary, an amplifier, buffer, or integrator added after the scanning circuit. 4 is a power supply for applying voltage to the sensor, but there is also a method of grounding this power supply and including this power supply in the reading circuit 3. 5 is a group of wires leading from the common gate of the thin film transistor of each block to the block drive circuit 1, and 6 is a common wire group connecting the corresponding bits of each block, that is, the signal lines coming out of the j-th bit of each block, to the reading circuit. In the wiring group in Fig. 1b, 7 shows the common electrode of the storage type image sensor, and 8 shows the 1-bit equivalent circuit of the storage type image sensor, and as shown in the figure, m sensor elements are arranged in one block. are arranged in an array. S
(i, j) indicates the j-th sensor element of the i block. Reference numeral 9 denotes a thin film transistor, and as shown in the figure, one thin film transistor is connected to each sensor bit, and their gates are shared and connected to the block drive circuit 1 by a wiring 10. A group of wires 5 is a group of n wires 10. Further, 11 is a wiring group leading to the reading circuit 3, and 6 is a wiring group in which the wirings coming out from bits S(1,j) to S(n,j) are common.

The outline of the operation is as follows. First, it is assumed that scanning is being performed and a signal charge is placed on the sensor. Starting from the 1st bit, the thin film transistor array of block 1 is turned on by the block drive circuit 1, and the signal charges of the sensor elements from the 1st bit to the mth bit are detected by the m detection circuits of the reading circuit 3. They are simultaneously detected and sequentially switched from 1 bit to m bits using a switch array in the reading circuit to read the signals. At this time, the timing of turning off the thin film transistor array can be considered in several ways depending on where the reading time of the reading circuit falls, but at least it must be completely turned off by the time the thin film transistor array of the next block is switched on.
Finally, the charge remaining in the reading circuit is completely reset, and switching of the thin film transistor array of the next block begins. This operation is continued until n blocks. In this way, by switching the thin film transistors in one block only once and moving the charge once, it is possible to effectively increase the scanning speed even if thin film transistors with slow response speeds are used. For example, response speed
If a 100 μsec thin film transistor is used as a switch, 1 block is 10 bits, and the scanning speed of 1 bit in the reading circuit is 5 μsec, the scanning speed of 1 block will be 200 μsec to 250 μsec, and if this is changed to a uniform speed, 20 bits per bit. This means that switching is performed at a speed of ~25μsec. Thin film transistors take 200 μsec to turn on and off, so in this case, scanning can be done about 10 times faster than when scanning simply using thin film transistors.

In addition, since thin film transistors with slow response speeds can be used, by increasing the speed of the reading circuit and increasing the number of elements in one block (m), thin film transistors can be used even if their characteristics vary, and the yield can be reduced. improves. Therefore, it is possible to compensate for all the drawbacks of the thin film transistor mentioned above.

Next, the operation will be explained in detail while illustrating two embodiments of the detection circuit and the scanning circuit of the reading circuit and a switching timing chart.

Figures 2a, b and c show three embodiments of the reading circuit. In FIG. 2a, 12 represents a resettable integrator, and 13 represents a switching FET. Further, (1), (2), . . . (m) correspond to the first to mth signal lines of each block. In this embodiment the detection circuit is an integrator;
This integrator integrates the signal charge on the storage image sensor, converts the signal to voltage, and uses it for switching.
Read the signal by sequentially switching the FETs. If the integrator is then reset, the reading circuit returns to its initial state. In Figure 2b, 14 is a charge storage capacitor, 15 is a reset FET, 16 is a switching FET, 17 is an amplifier such as an integrator or a buffer, and when 17 is an integrator, the charge is stored in the charge storage capacitor. 15 reset FETs are used to
is not necessary.

In FIG. 2c, 18 is a detection circuit, and its configuration includes a first stage detector consisting of a readout resistor and a preamplifier (19), a sample hold circuit (20), and a sample hold circuit (21).
comparators, and 22 TTL and CMOS level converters. Further, 23 is a scanning circuit consisting of a parallel-to-serial conversion type shift register.
In this embodiment, the signal is binarized into a white level and a black level by the detection circuit, and this binarized signal is scanned by a shift register. Further, depending on the configuration of the subsequent signal processing system, it is also possible to process one block of signals as they are without performing scanning using a shift register.

The timings of the switching pulses in the embodiments shown in FIGS. 2a and 2b are shown in FIGS. 3a and 3.
It is b. FIG. 3a shows a case where 17 is a buffer in the embodiment of FIG. 2a and the embodiment of FIG. 2b, and the operation is as described above. Also, Figure 3b
is the case where 17 is an integrator in the configuration shown in Figure 2b,
The reset pulse shown here enters the integrator 17 reset circuit. Since there is only one integrator in operation, it is necessary to reset the integrator for each bit, and as mentioned above, there is no need for a reset FET.
They are basically the same, except that all bits are not reset at the same time.

Next, FIGS. 4a and 4b show examples of the timing of switching of the thin film transistor array and the operation of the reading circuit, and the section B in the figure corresponds to the section B shown in FIG. 3. In FIG. 4, c and e are block switching pulses output from the block drive circuit, and two blocks are shown in the figure. d and f are response waveforms of the thin film transistor.

As is clear from the figure, in Fig. 4a, the signal charges transferred to the reading circuit are sequentially read after the thin film transistor is completely turned off, and in Fig. 4b, the signal charges transferred to the reading circuit are sequentially read after the thin film transistor is completely turned off. Start reading the signal. The former is the timing when the noise accompanying switching of the thin film transistor is too large to be ignored relative to the signal charge, and the latter is the timing when the noise is negligible. This noise is mainly due to the feedthrough of the switching pulse through the capacitance between the gate and source or drain of the thin film transistor, and the fluctuation of the channel charge accompanying ON-OFF operations, as shown in Figure 4a. By doing this, it is possible to generate anti-phase noise and cancel it. A subsequent read operation provides a signal with reduced noise. However, if such noise is sufficiently small, the timing shown in FIG. 4b, which can increase the block scanning speed, is better. Note that these two examples are not all about timing.

What I would like to emphasize here is that this method is essentially different from the signal readout method using a matrix type drive circuit as shown in FIG. 5 of the solid-state photoelectric conversion device of the present invention. The difference between Fig. 5 and Fig. 1a is in the parts 24 and 25, where 24 is a switching FET capable of high-speed switching, and the switching FET 25 is a readout circuit using a resistor and a video amplifier, which is generally used for signal readout of storage type image sensors. This is a readout circuit such as an integrator. Although the circuits are very similar, in this circuit, even if a switching pulse is sent from the block drive circuit 1 to the gate of the thin film transistor of the block, unless the switching FET 24 is turned on, the pulse between the source and drain of the thin film transistor is Regardless of the electric field, the thin film transistor does not turn on. The thin film transistor starts to turn on when the switching FET connected to the thin film transistor
No matter how fast the switching FET is, it takes time for the thin film transistor to turn on and off to read one bit, and the operating speed will not increase at all.

Next, FIG. 6 shows an embodiment of the storage type image sensor element and the thin film transistor. In this embodiment, amorphous silicon is used as the material for both the sensor and the transistor, and 26 is a glass substrate;
27 is a transparent common electrode such as SnO ₂ or ITO, 28 is a
A shield made of metal such as Cr determines the length of the sensor opening in the sub-scanning direction. 29 has a thickness of 100~
The Si ₃ N ₄ film 30 with a thickness of approximately 200 Å is an amorphous silicon film with a thickness of 2 to 3 μm doped with boron, oxygen, etc. to have a high resistance, and 31 is a p-type film doped with boron and with a thickness of 0.2 to 0.4 μm. With amorphous silicon film, 2
9 and 31 are blocking layers that serve to prevent charge injection; 30 is a layer that generates charges by light; 29 to 31 constitute an accumulation type image sensor. 32 is an Al electrode that serves as the upper individual electrode of the sensor and the drain electrode of the thin film transistor, and 33 is an Al electrode that serves as the upper individual electrode of the sensor and the drain electrode of the thin film transistor.
Al source electrode, 34 is a non-doped amorphous silicon film with a film thickness of about 1 to 2 μm, and 35 is a film thickness of 0.1 to 2 μm.
It is a 0.5 μm Si ₃ N ₄ film and is an insulating layer for thin film transistors. 36 is an Al gate electrode 33 to 36
to form a thin film transistor. 37 is a light shielding film that prevents light from entering the thin film transistor; if the structure of the device allows light to enter from the side where the element is located, it must also be placed on the thin film transistor. This is because the amorphous silicon used in thin film transistors has photoconductivity. 38 is light from the original.

As in this embodiment, the sensor part and the thin film transistor part of the solid-state photoelectric conversion device of the present invention can be formed on the same substrate with the same material, or depending on the manufacturing method, they can be formed continuously using the same manufacturing equipment. It can also be manufactured with good productivity, reliability, and at low cost. Other examples include Sachicon, CdS, or
Those using CdSe, etc., thin film transistors using CdS, CdSe, etc. as materials, and Si
The material may be polycrystalline Si formed by vapor deposition or polycrystalline silicon formed by laser annealing.

As described above, according to the present invention, a high-sensitivity and high-speed accumulation type image sensor is used, and a dedicated IC is used.
A solid-state photoelectric conversion device having an unnecessary drive circuit can be obtained, which is useful for speeding up, downsizing, and lowering the price of facsimile devices.

[Brief explanation of drawings]

Figures 1a and 1b show the basic configuration of the contact type image sensor of the present invention, and Figures 2a, b, and c show the reading circuit section 1.
Two embodiments of the section, Figures 3a and b are timing charts for switching in the reading circuit, Figure 4.
Figures a and b show an example of the timing of block switching and reading circuit switching, Figure 5 shows a contact type image sensor with a matrix type drive circuit, and Figure 6 shows an example of an accumulation type image sensor and a thin film transistor. ing. 1... Block drive circuit, 2... 1 block of storage type image sensor and thin film transistor array, 3... Reading circuit, 4... Power supply, 5... Wiring group, 6... Common wiring group, 7... Common electrode , 8...
Storage type image sensor element, 9... Thin film transistor, 10... Common gate, 11... Wiring group, 1
2... Integrator, 13, 16... For switching
FET, 14...Signal charge storage capacitor, 1
5... Reset FET, 17... Buffer or integrator, 18... Detection circuit, 19... First stage detection circuit, 20... Sample hold circuit, 21... Comparator, 22... Level converter, 23... Shift register, 24...Switching FET,
25...Detection circuit, 26...Glass substrate, 27...
... Common electrode, 28 ... Light shielding film, 29 ... Si ₃ N ₄
Film, 30... High resistance amorphous silicon film, 31...
P-type amorphous silicon film, 32... Upper individual electrode of the sensor that also serves as a drain electrode, 33... Source electrode, 34... Amorphous silicon film, 35... Si ₃ N ₄
Film, 36... Gate electrode, 37... Light shielding film, 38
...Signal light.

Claims (1)

[Scope of Claims] 1. In a one-dimensional or two-dimensional image sensor that operates in an accumulation type, a thin film transistor is provided in series for each photoelectric conversion element, and the thin film transistors are divided into blocks each having the same number,
It is equipped with a sensor section characterized in that the gates of the thin film transistors in the same block are shared, and by connecting the corresponding thin film transistors for each block, it is possible to connect the same number of detection circuits as the elements in one block. The output is guided to a reading circuit consisting of a scanning circuit, and a group of thin film transistors is turned on.
A solid-state photoelectric conversion device is characterized in that it simultaneously detects the signals of the blocks and scans and reads them. 2. The photoelectric conversion element according to claim 1, in which the structure of the element excluding the electrodes consists of a Si ₃ N ₄ film, a high-resistance amorphous silicon film, and a p-type amorphous silicon film from the light incident side. Solid-state photoelectric conversion device. 3. The solid-state photoelectric conversion device according to claim 1, wherein the thin film transistor uses amorphous silicon as a material and uses a Si ₃ N ₄ film or a SiO ₂ film as an insulating film. 4. The solid-state photoelectric conversion device according to claim 1, which has a reading circuit in which the detection circuit is an integrator or a sample hold circuit, and the scanning circuit is an analog switch. 5. The solid-state photoelectric conversion device according to claim 1, wherein the detection circuit includes a circuit that binarizes a signal, and the scanning circuit includes a reading circuit that is a shift register.