JP2001074552A - Photoelectric transfer device and driving method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce in a short time a potential variation at the time when a potential of a signal line or a sensor bias line comes down for an instant. SOLUTION: This device has a photoelectric transfer element group arranged two-dimensionally with photoelectric transfer elements connected to sensors and switch elements respectively, plural drive lines connected respectively to the plural switch elements arranged along one direction of the photoelectric transfer element group, plural signal lines connected respectively to output sides of the plural switch elements arranged along the other direction of the photoelectric transfer element group, and a control means for driving the plural drive lines, for turning the switch elements connected the respective drive lines on, to connect the signal lines and the sensors. In a refresh mode of the photoelectric transfer element, the signal lines are brought into a set potential, the drive lines g1-g3 are driven unidirectionally in oreder by the control means, and timings for driving the respective drive lines g1, g2, g3 are made not to be overlapped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device and a method of driving the same, and more particularly to a photoelectric conversion device formed using a large-area process, such as a facsimile, a digital copying machine or an X-ray imaging device. The present invention relates to a photoelectric conversion device suitably used for a two-dimensional photoelectric conversion device and a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, a reading system using a reduction optical system and a CCD type sensor has been used as a reading system of a facsimile, a digital copying machine or an X-ray imaging apparatus. , A-S
With the development of photoelectric conversion semiconductor materials typified by i), the development of a so-called contact type sensor, in which a photoelectric conversion element and a signal processing unit are formed on a large-area substrate and read by an information source and an optical system of the same magnification, has been developed. Remarkable. In particular, since a-Si can be used not only as a photoelectric conversion material but also as a thin film field effect transistor (hereinafter, referred to as TFT), an advantage that a photoelectric conversion semiconductor layer and a semiconductor layer of a TFT can be formed simultaneously. have.

[0003]

However, the characteristic specifications of a large-area photoelectric conversion device are becoming stricter year by year. Particularly, in a two-dimensional photoelectric conversion device such as an X-ray imaging device which performs reading at the same magnification, X that affects the human body
It is required to reduce the number of lines as much as possible and to obtain more accurate data uniformly and in a short time in a two-dimensional area. In response to such a demand, the variation in the signal output of the photoelectric conversion element is reduced. In order to make the sensor sufficiently small, it is conceivable to devise the operation of the drive line in the sensor refreshing method.

[0004]

According to the present invention, there is provided a photoelectric conversion device comprising: a photoelectric conversion element group in which a plurality of two-dimensionally arranged photoelectric conversion elements each having a sensor and a switch element connected thereto; A plurality of drive lines respectively connected to the plurality of switch elements arranged in one direction of a group,
A plurality of signal lines respectively connected to the output sides of the plurality of switch elements arranged in the other direction of the photoelectric conversion element group; and the switch elements driving the plurality of drive lines and connected to the respective drive lines Control means for turning on the signal line and the sensor, and wherein the photoelectric conversion element is driven in a photoelectric conversion mode, a signal charge transfer mode, and a refresh mode. In the refresh mode, the signal line is set to a reset potential, the control unit sequentially drives the drive lines in the one direction, and the timing for driving each drive line is not overlapped.

According to a method of driving a photoelectric conversion device of the present invention, a plurality of photoelectric conversion elements each having a sensor and a switch element connected thereto are two-dimensionally arranged, and the switch elements are connected to drive lines line by line. The driving lines are sequentially driven in one direction, signal charges are transferred to signal lines arranged in a direction different from the one direction, and signal reading is sequentially performed. The photoelectric conversion element includes a photoelectric conversion mode and a signal charge transfer mode. And a driving method of the photoelectric conversion device driven in the refresh mode,
In the refresh mode, the signal line is set to a reset potential, the drive lines are sequentially driven in the one direction, and the timings at which the drive lines are turned on do not overlap.

The present invention operates so that the output of a plurality of signals in a two-dimensional area can be made substantially uniform.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 2A and 2B are schematic views showing the structure of a photoelectric conversion element according to the present invention. FIG. 2B shows FIG.
FIG. 3A is a cross-sectional view when cut along line AB in FIG.
As shown in FIG. 2, the photoelectric conversion element includes a sensor 8 on a glass substrate 7 and a TFT 9. In FIG. 2, the sensor 8 and the TFT 9 are formed simultaneously by an amorphous silicon thin film process. The sensor 8 is a MIS type sensor. For the sensor 8 and the TFT 9, a lower metal layer 10, an insulating layer 11, a semiconductor layer 12, an n ⁺ layer 13, an upper metal layer 14, and a protection layer (not shown) such as an amorphous silicon nitride film or polyimide are sequentially formed on a glass substrate 7. Is formed by patterning.

FIG. 3 is an equivalent circuit showing the operation of the photoelectric conversion element of FIG. An electric charge is generated according to the amount of light incident on the sensor 8, and the electric charge is transferred to a reading device (not shown) by the TFT 9, thereby performing a reading operation.

Next, FIG. 4 shows an overall circuit diagram of a photoelectric conversion device in which 3 × 3 photoelectric conversion elements shown in FIG. 3 are arranged.

In FIG. 4, S11 to S33 are photoelectric conversion elements, and the lower electrode side is denoted by G and the upper electrode side is denoted by D.
C11 to C33 are storage capacitors, which are shown in the equivalent circuit as described above because the photoelectric conversion elements S11 to S33 function as capacitors. T11 to T33 are T for transfer
FT. Vs is a read power supply and Vg is a refresh power supply, which are connected to the D electrodes of all the photoelectric conversion elements S11 to S33 via switches SWs and SWg, respectively. The switch SWs is connected to the refresh control circuit RF via the inverter via the inverter, and the switch SWg is controlled to be turned on during the refresh period.

The photoelectric conversion device divides a total of nine pixels into three blocks and simultaneously transfers the outputs of three pixels per block, and detects the integrated circuit I for detection through this signal line SIG.
The output is sequentially converted by C and output (Vout).
Each pixel is two-dimensionally arranged by arranging three pixels in one block in the horizontal direction and sequentially arranging the three blocks in the vertical direction.

Further, cesium iodide (C
A phosphor such as sI) may be formed. X from above
When the line (X-ray) enters, it is converted into light by the phosphor, and this light enters the photoelectric conversion element.

Next, the operation of the photoelectric conversion device will be described. First, the operation of the photoelectric conversion device according to the prior art of the present invention will be described with reference to the timing charts of FIGS.

First, shift registers SR1 and SR
2, the Hi level is applied to the control wirings g1 to g3 and s1 to s3. Then, the transfer TFTs T11 to T33 and the switches M1 to M3 are turned on to conduct, and the G electrodes of all the photoelectric conversion elements S11 to S33 are set to the GND potential (the input terminal of the integration detector Amp is designed to the GND potential. Because). At the same time, the refresh control circuit RF outputs the Hi level, the switch SWg turns on, and all the photoelectric conversion elements S11 to S11 are turned on.
The D electrode in S33 becomes positive potential by the refresh power supply Vg. Then, all the photoelectric conversion elements S11 to S33 enter the refresh mode and are refreshed. Next, the refresh control circuit RF outputs Lo level and the switch SW
s is turned on, and the D electrodes of all the photoelectric conversion elements S11 to S33 have a higher positive potential by the reading power supply Vs. Then, all the photoelectric conversion elements S11 to S33 enter the photoelectric conversion mode, and the capacitors C11 to C33 are initialized at the same time. In this state, the Lo level is applied to the control lines g1 to g3 and s1 to s3 by the shift registers SR1 and SR2.
Then, the switches M1 of the transfer TFTs T11 to T33
M3 is turned off, and the G electrodes of all the photoelectric conversion elements S11 to S33 are DC open, but the capacitors C11 to C3 are open.
3 holds the potential. However, at this time, since no X-rays are incident, all the photoelectric conversion elements S11 to S33
No light enters and no photocurrent flows. In this state, when the X-rays are emitted in a pulsed manner, pass through the human body or the like and enter the fluorescent material, they are converted into light, and the light is converted into the respective photoelectric conversion elements S1.
1 to S33. This light contains information on the internal structure of the human body and the like. The photocurrent flowing by this light is accumulated as a charge in each of the capacitors C11 to C33 and X
It is retained even after the end of the line incidence.

Next, a high-level control pulse is applied to the control line g1 by the shift register SR1, and the control pulse is applied to the control lines s1 to s3 of the shift register SR2, whereby the switch M1 of the transfer TFTs T11 to T33 is applied.
V1 to v3 are sequentially output through. Similarly, other optical signals are sequentially output under the control of the shift registers SR1 and SR2. Thereby, two-dimensional information of the internal structure of the human body or the like is obtained as v1 to v9. The operation up to this point is performed to obtain a still image, but the operation up to here is repeated to obtain a moving image.

In the above photoelectric conversion device, the D electrode of the photoelectric conversion element is connected in common, and this common wiring is connected to the switch SWg.
And the switches SWs, the potential of the refresh power supply Vg and the potential of the read power supply Vs are controlled, so that all the photoelectric conversion elements can be simultaneously switched to the refresh mode and the photoelectric conversion mode. Therefore, light output can be obtained with one TFT per pixel without complicated control.

In the operation shown in FIG. 5, since the refresh operation is performed simultaneously on all the Vg drive lines, the on-pulses g1 to g3 fall at the same time.

Each of the drive lines g1 to g3 is supplied with a signal at the moment when the on-pulses of g1 to g3 simultaneously fall due to the cross portion capacitance CCR1 between the drive line and the signal line and the cross portion capacitance CCR2 between the drive line and the sensor bias line in FIG. The potential of the line and the sensor bias line drops momentarily.

After a momentary drop in the potential of the signal line and the sensor bias line, the potential is restored to the original potential by the respective time constants.

However, if there is not enough time for each potential to return to the original potential after a momentary drop, that is, after turning on the X-ray in FIG. 5 and performing photoelectric conversion by the sensor, If the time until the signal charge is transferred by the TFT after turning on g1 is not sufficient, the signal charge is transferred before the potential of the signal line or the sensor bias line is restored to the original potential. In some cases, a sufficient output cannot be obtained.

Also, when the time constant of each of the signal line and the sensor bias line cannot be reduced, that is, when the wiring resistance of the signal line or the sensor bias line is large, or when the stray capacitance is large, the signal line or the sensor bias line is Since the signal charge is transferred before the potential of the signal has recovered to the original potential, it may be considered that an ideal output cannot be sufficiently obtained.

This is because the signal output Vout depends on the potential of the signal line or the sensor bias line.

In such a case, the signal output at the beginning of reading when reading out the signal charge, that is, Vout in FIG.
It is possible that the output of v1 is slightly not ideal.

According to the present invention, in order to make the output of a plurality of signals in the two-dimensional area more uniform and to further improve the quality of the panel, the fall timing of the on-pulses g1 to g3 as described above is shifted. By doing so, the amount of potential change when the potential of the signal line or the sensor bias line falls for a moment can be reduced.

FIG. 1 is a timing chart showing an operation for explaining an embodiment according to the present invention. The same operations as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

A characteristic point of the timing chart shown in FIG. 1 is that the timings of the on-pulses g1 to g3 are shifted as described above. This makes it possible to reduce the amount of potential change when the potential of the signal line or the sensor bias line drops for a moment, and as a result, the time required for the potential of the signal line or the sensor bias line to recover to the original potential is reduced.

A further characteristic point is that the timings at which the drive lines (g1, g2, and g3) are turned on do not overlap in how to shift the timings of the on-pulses g1 to g3. By driving the drive lines so that the timings at which the drive lines are turned on do not overlap, the drive lines g1 to g
3 can reduce the amount of potential change that lowers the potentials of the signal line and the sensor bias line at the moment of falling by the cross capacitance CCR1 between the drive line and the signal line and the cross capacitance CCR2 between the drive line and the sensor bias line. Will be possible.

As described above, when the timing of the on-pulse of the driving line at the time of refresh is shifted so that the timing of turning on each driving line does not overlap, the driving is performed when the potential of the signal line or the sensor bias line drops for a moment. Makes it possible to further reduce the potential change amount of
As a result, it is possible to make the output of a plurality of signals in the two-dimensional area substantially sufficiently uniform, and to further improve the quality of the panel.

In the above photoelectric conversion device, nine pixels are divided into 3 × 3 pixels.
The two-dimensional arrangement is performed, and three pixels are simultaneously transferred and output three times at a time, but the present invention is not limited to this.
An X-ray detector of 40 cm × 40 cm can be obtained by arranging × 5 pixels two-dimensionally as 2000 × 2000 pixels. If this is combined with an X-ray generator instead of an X-ray film to constitute an X-ray radiograph, it can be used for chest X-ray examination and breast cancer examination. Then, unlike the film, the output can be instantly projected on a display device such as a CRT, and further, the output can be converted into digital, processed by a computer, and converted into an output suitable for the purpose. It can also be stored on an information recording medium such as a magneto-optical disk, and past images can be searched instantaneously. Also, the sensitivity is better than that of a film, and a clear image can be obtained with weak X-rays having little effect on the human body.

FIG. 6 shows an example. Here, 101 is a patient, 102 is an X-ray source, 103 is a phosphor, 104 is a photoelectric conversion device, 105 is an imaging switch, 106 is a display, 107 is a control circuit, and 108 is a drive circuit. FIG.
, An X-ray imaging apparatus comprising a phosphor that converts X-rays into light, a two-dimensional sensor panel, an X-ray source, an X-ray source driving circuit, and an X-ray source control circuit is configured.

[0032]

As described above, the potential of the signal line or the sensor bias line is instantaneously driven by shifting the on-pulse timing of the drive line at the time of refreshing so that the timing of turning on each drive line does not overlap. As a result, it is possible to further reduce the amount of change in the potential at the time of falling, and as a result, it is possible to make the output of a plurality of signals in the two-dimensional area substantially uniform, thereby further improving the quality of the panel.

[Brief description of the drawings]

FIG. 1 is a timing chart showing an operation for explaining a first embodiment according to the present invention.

FIG. 2A is a plan view of each component in a photoelectric conversion device according to the present invention, and FIG. 2B is a cross-sectional view thereof.

FIG. 3 is an equivalent circuit of one element in the photoelectric conversion device according to the present invention.

FIG. 4 is an overall circuit diagram of the photoelectric conversion device according to the present invention.

FIG. 5 is a timing chart showing the operation of the photoelectric conversion device according to the prior art.

FIG. 6 is a schematic configuration diagram showing an X-ray imaging system.

[Explanation of symbols]

 S11 to S33 Sensor T11 to T33 TFT C11 to C33 Capacitor SR1, SR2 Shift register IC Detection integrated circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H01L 31/10 H01L 31/10 G (72) Inventor Noriyuki Kaibe 3-30 Shimomaruko, Ota-ku, Tokyo 2 Canon Inc. (72) Inventor Toshikazu Tamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A photoelectric conversion element group in which a plurality of photoelectric conversion elements in which a sensor and a switch element are connected are arranged two-dimensionally, and a plurality of the switch elements arranged in one direction of the photoelectric conversion element group. A plurality of drive lines respectively connected, a plurality of signal lines respectively connected to output sides of the plurality of switch elements arranged in the other direction of the photoelectric conversion element group, and driving the plurality of drive lines; Control means for turning on the switch element connected to each drive line to connect the signal line and the sensor, wherein the photoelectric conversion element includes a photoelectric conversion mode, a signal charge transfer mode, and a refresh mode. In the photoelectric conversion device driven by the above, in the refresh mode, the signal line is set to a reset potential, and the control unit sequentially drives the drive line in the one direction, and The photoelectric conversion device is characterized in that as the timing for driving the drive line do not overlap. 2. The terminal according to claim 1, wherein the terminals of all the sensors on the side opposite to the connection side of the switch element are connected to a wiring whose potential is switched at least between a photoelectric conversion mode and a refresh mode. Photoelectric conversion device. 3. The photoelectric conversion device according to claim 1, wherein the sensor and the switch element are provided on the same substrate. 4. The device according to claim 1, wherein the sensor and the switch element each include a first electrode layer, an insulating layer, a semiconductor layer, a high-concentration impurity semiconductor layer, and a second electrode layer. 4. The photoelectric conversion device according to 3. 5. A first electrode layer, an insulating layer, a photoelectric conversion semiconductor layer, a semiconductor layer for preventing injection of carriers of the first conductivity type,
A photoelectric conversion element configured by laminating a second electrode layer and a second electrode layer on the same substrate; and a first conductivity type carrier generated by signal light incident on the photoelectric conversion semiconductor layer. A photoelectric conversion unit that applies an electric field to the photoelectric conversion element in a direction that guides a carrier of a second conductivity type different from the first conductivity type to the second electrode layer; Refresh means for applying an electric field to the photoelectric conversion element in a direction in which carriers of one conductivity type are guided from the photoelectric conversion semiconductor layer to the second electrode layer, and the photoelectric conversion semiconductor layer during the photoelectric conversion operation by the photoelectric conversion means. 2. The photoelectric conversion device according to claim 1, further comprising: a signal detection unit configured to detect the accumulated first conductivity type carrier or the second conductivity type carrier guided to the second electrode layer. 3. 6. A photoelectric conversion device having a wavelength converter on the image information reading section side of the photoelectric conversion device according to claim 1. Description: 7. The photoelectric conversion device according to claim 6, wherein the wavelength converter is a phosphor. 8. A plurality of photoelectric conversion elements each having a sensor and a switch element connected thereto are two-dimensionally arranged, the switch elements are connected to drive lines line by line, and the drive lines are sequentially driven in one direction. Transferring signal charges to signal lines arranged in a direction different from the one direction and sequentially reading out signals, wherein the photoelectric conversion element is driven in a photoelectric conversion mode, a signal charge transfer mode, and a refresh mode. In the driving method of the device, in the refresh mode, the signal line is set to a reset potential, the driving lines are sequentially driven in the one direction, and the timings at which the driving lines are turned on do not overlap. For driving a photoelectric conversion device.