JP4646997B2 - Driving method of photoelectric conversion device - Google Patents

Description

  The present invention relates to a method for driving a photoelectric conversion device, and more particularly to a photoelectric conversion device formed by using a large area process, for example, a two-dimensional photoelectric conversion device that performs the same magnification reading such as a facsimile, a digital copying machine, or an X-ray imaging device. The present invention relates to a suitably used photoelectric conversion device and driving method.

  Conventionally, a reading system using a reduction optical system and a CCD type sensor has been used as a reading system for a facsimile, a digital copying machine, an X-ray imaging apparatus, etc. In recent years, hydrogenated amorphous silicon (hereinafter referred to as a-Si) is used. The development of a photoelectric conversion semiconductor material represented by the following describes 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 optical system of the same magnification as an information source. In particular, 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), so that the photoelectric conversion semiconductor layer and the TFT semiconductor layer can be formed simultaneously. have.

  However, characteristic specifications for large-area photoelectric conversion devices are becoming stricter year by year. Particularly in a two-dimensional photoelectric conversion device that performs the same magnification reading such as an X-ray imaging device, X-rays that affect the human body are slightly affected. However, it is required to obtain highly accurate data uniformly in a two-dimensional area in a short time, and in response to such a request, the variation in the signal output of the photoelectric conversion element is reduced as much as possible. In order to drive in a short time, it is conceivable to devise the operation of the drive line in the sensor refresh method.

A method for driving a photoelectric conversion device according to the present invention is such that pixels each including a photoelectric conversion element having two electrode layers and a switch element connected to one electrode layer of the photoelectric conversion element are in a row direction and a column direction. Is arranged in multiple,
A plurality of drive lines connected to the plurality of switch elements arranged in the row direction and a plurality of signal lines connected to the plurality of switch elements arranged in the column direction;
Control means for applying a pulse having a pulse width for turning on the switch element and a falling edge for turning off the switch element to each drive line; and the other of the photoelectric conversion elements of the plurality of pixels A power source having a wiring commonly connected to the electrode layers of the first and second potentials different from the first potential for the photoelectric conversion element to perform photoelectric conversion; A method of driving a photoelectric conversion device having
In a refresh operation in which a plurality of the pulses are applied to the plurality of drive lines while the wiring is set to the second potential and the plurality of signal lines are set to a predetermined potential,
Among the plurality of pulses applied to the plurality of drive lines, the falling timing of the pulse is shifted between the two pulses applied successively, and the two pulses This is a method for driving a photoelectric conversion device in which the pulse widths partially overlap.

  In the present invention, it is possible to make a plurality of signal outputs in a two-dimensional area uniform in a relatively short time by overlapping timings at which at least two continuous drive lines are turned on. Works.

  As described above, the potential of the signal line or sensor bias line is momentarily lost by driving the on-line timing of the drive line at the time of refreshing so that at least the two consecutive drive lines turn on. It is possible to reduce the amount of potential change within a short time within a relatively short refresh time, and as a result, multiple signal outputs in the two-dimensional area are made more uniform in a short time, further improving the panel quality. It becomes possible to make it.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

2A and 2B are schematic views showing the configuration of the photoelectric conversion element according to the present invention. FIG. 2B is a cross-sectional view of FIG. 2A taken along line AB. As shown in FIG. 2, the photoelectric conversion element includes a sensor 8 and a TFT 9 on a glass substrate 7. In FIG. 2, the sensor 8 and the TFT 9 are simultaneously formed 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 protective layer (not shown) (such as an amorphous silicon nitride film or polyimide) are sequentially formed on a glass substrate 7. , By patterning.

  FIG. 3 is an equivalent circuit showing the function of the photoelectric conversion element of FIG. A charge is generated according to the amount of light incident on the sensor 8, and the charge is transferred to a reading device (not shown) by the TFT 9 to perform 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 indicated by G and the upper electrode side is indicated by D. C11 to C33 are storage capacitors, and the photoelectric conversion elements S11 to S33 function as capacitors and are shown in this way on the equivalent circuit. T11 to T33 are transfer TFTs. Vs is a power source for reading and Vg is a power source for refreshing, 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 directly connected to the refresh control circuit RF 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 output of three pixels per block, and is sequentially converted into an output by the detection integrated circuit IC through this signal wiring SIG and output (Vout). . Each pixel is arranged two-dimensionally by arranging three pixels in one block in the horizontal direction and arranging the three blocks in the vertical direction in order.

  In addition, a phosphor such as cesium iodide (CsI) may be formed on the top of the pixel. When X-rays (X-ray) are incident from above, the phosphors convert the light into light, and the 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 as the prior art of the present invention will be described with reference to the timing charts of FIGS.

  First, the Hi level is applied to the control wirings g1 to g3 and s1 to s3 by the shift registers SR1 and SR2. Then, the transfer TFTs T11 to T33 and the switches M1 to M3 are turned on and become conductive, 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 a Hi level, the switch SWg is turned on, and the D electrodes of all the photoelectric conversion elements S11 to S33 are set to a 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 a Lo level, the switch SWs is turned on, and the D electrodes of all the photoelectric conversion elements S11 to S33 are set to a higher positive potential by the reading power source 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 wirings g1 to g3 and s1 to s3 by the shift registers SR1 and SR2. Then, the switches M1 to M3 of the transfer TFTs T11 to T33 are turned off, and the G electrodes of all the photoelectric conversion elements S11 to S33 are opened in terms of DC, but the potential is held by the capacitors C11 to C33. However, since no X-rays are incident at this time, no light enters the photoelectric conversion elements S11 to S33 and no photocurrent flows. In this state, X-rays are emitted in a pulsed manner, pass through the human body, etc., and enter the phosphor, and are converted into light, and the light enters each of the photoelectric conversion elements S11 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 in each of the capacitors C11 to C33 as electric charges and is held even after the X-ray incidence is completed.

  Next, a Hi-level control pulse is applied to the control wiring g1 by the shift register SR1, and v1 to v3 through the switches M1 to M3 of the transfer TFTs T11 to T33 by applying control pulses to the control wirings s1 to s3 of the shift register SR2. Are output sequentially. Similarly, other optical signals are sequentially output under the control of the shift registers SR1 and SR2. Thereby, the two-dimensional information of the internal structure of the human body or the like is obtained as v1 to v9. The operation so far is performed when a still image is obtained, but the operation so far is repeated when a moving image is obtained.

  In the photoelectric conversion device, the D electrodes of the photoelectric conversion elements are connected in common, and the common wiring is controlled to the potentials of the refresh power supply Vg and the read power supply Vs via the switches SWg and SWs. The conversion element can be simultaneously switched between 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 of FIG. 5, since the refresh operation is performed simultaneously for all Vg drive lines, the on pulses of g1 to g3 fall simultaneously.

  Each of the drive lines g1 to g3 is connected to the signal line and the sensor at the moment when the ON pulses of g1 to g3 fall at the same time due to the cross section capacitance CCR1 of the drive line and the signal line and the cross section capacitance CCR2 of the drive line and the sensor bias line in FIG. The potential of the bias line drops for a moment.

  The potentials of the signal line and the sensor bias line are restored to the original potential by the respective time constants after a moment.

  However, after a short time for each potential, if it is not enough time to recover to the original potential, that is, X-ray is turned on in FIG. 5 and photoelectric conversion is performed by the sensor, and then g1 is turned on. If the time until the signal charge is transferred by the TFT is not sufficient, the signal charge is transferred before the potential of the signal line or sensor bias line is restored to the original potential. It is conceivable that a sufficient value cannot be obtained.

  In addition, 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 the stray capacitance is large, the potential of the signal line or the sensor bias line is Since the signal charge is transferred before the original potential is restored, there may be a case where an ideal output cannot be obtained sufficiently.

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

  In such a case, there may be a case where the signal output at the beginning of reading when reading out signal charges, that is, the output of v1 of Vout in FIG.

  In the present invention, in order to make a plurality of signal outputs in a two-dimensional area more uniform and further improve the quality of the panel, the timing of falling of the on-pulses of 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. In addition, the same code | symbol is attached | subjected to the part of the same operation | movement as FIG. 5, and description is abbreviate | omitted.

  A characteristic point in the timing chart shown in FIG. 1 is that the on-pulse timings of 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 sensor bias line falls for a moment, and as a result, the time for restoring the potential of the signal line or sensor bias line to the original potential is shortened.

  Furthermore, the characteristic point is that the timing at which at least two continuous drive lines (g1 and g2, or g2 and g3) are turned on overlaps by about half the width of the pulse in the way of shifting the timing of the on pulses of g1 to g3. It is a point. Thus, by driving so that at least two continuous drive lines are turned on, the time for refreshing all the drive lines can be shortened, and high-speed driving like a moving image becomes possible.

  As described above, the potential of the signal line or sensor bias line is momentarily lost by driving the on-line timing of the drive line at the time of refreshing so that at least the two consecutive drive lines turn on. It is possible to reduce the amount of potential change within a short time within a relatively short refresh time, and as a result, multiple signal outputs in the two-dimensional area are made more uniform in a short time, further improving the panel quality. It becomes possible to make it.

  In the above photoelectric conversion device, nine pixels are two-dimensionally arranged in 3 × 3, and three pixels are divided and transferred at the same time three times. However, the present invention is not limited to this. For example, 5 × 5 pixels per 1 mm in length and width If it is arranged two-dimensionally as 2000 × 2000 pixels, an X-ray detector of 40 cm × 40 cm can be obtained. If this is combined with an X-ray generator instead of an X-ray film to constitute an X-ray X-ray apparatus, it can be used for chest X-ray screening and breast cancer screening. Then, unlike film, the output can be instantly displayed on a display device such as a CRT, and the output can be converted to digital and converted into an output suitable for the purpose by computer processing. It can also be stored in an information recording medium such as a magneto-optical disk, and past images can be retrieved instantly. It is also possible to obtain a clear image with weak X-rays that have better sensitivity than films and have little effect on the human body.

  An example is shown in FIG. 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. In FIG. 6, an X-ray imaging apparatus comprising a phosphor that converts X-rays into light, a two-dimensional sensor panel, an X-ray source, a drive circuit for the X-ray source, and a control circuit for the X-ray source is configured.

It is a timing chart which shows the operation | movement for demonstrating the 1st Example which concerns on this invention. (A) is a top view of each component in the photoelectric conversion apparatus concerning this invention, (b) is the sectional drawing. 2 is an equivalent circuit of one element in the photoelectric conversion device according to the present invention. It is a whole circuit diagram in the photoelectric conversion apparatus concerning this invention. It is a timing chart which shows operation | movement of the photoelectric conversion apparatus concerning a prior art. 1 is a schematic configuration diagram showing an X-ray imaging system.

Explanation of symbols

S11-S33 sensor T11-T33 TFT
C11 to C33 Capacitors SR1, SR2 Shift register IC Integrated circuit for detection

Claims (8)

A plurality of pixels each having a photoelectric conversion element having two electrode layers and a switch element connected to one electrode layer of the photoelectric conversion element are arranged in a row direction and a column direction,
A plurality of drive lines connected to the plurality of switch elements arranged in the row direction and a plurality of signal lines connected to the plurality of switch elements arranged in the column direction;
A control means for applying a pulse having a pulse width for turning on the switch element and a falling edge for turning the switch element from ON to each drive line; and the other of the photoelectric conversion elements of the plurality of pixels And a power source having a wiring commonly connected to the electrode layer of the first and second potentials different from the first potential for the photoelectric conversion element to perform photoelectric conversion; A method of driving a photoelectric conversion device having
In a refresh operation in which a plurality of the pulses are applied to the plurality of drive lines while the wiring is at the second potential and the plurality of signal lines are at a predetermined potential,
Among the plurality of pulses applied to the plurality of drive lines, the timing of the falling of the pulse is shifted between the two pulses applied successively, and the two pulses A method for driving a photoelectric conversion device in which the pulse widths of the portions overlap.   The photoelectric conversion element includes the one electrode layer, the other electrode layer, an insulating layer provided between the one electrode layer and the other electrode layer, the insulating layer, and the other electrode. The photoelectric conversion according to claim 1, further comprising: a semiconductor layer provided between the semiconductor layer and a high-concentration impurity semiconductor layer provided between the semiconductor layer and the other electrode layer. Device driving method.   3. The phosphor according to claim 1, further comprising a phosphor that converts X-rays into light on the plurality of photoelectric conversion elements, wherein the X-rays are incident on the phosphor in a pulsed manner. Driving method of the photoelectric conversion device.   The power supply is one of a read power supply for setting the wiring to the first potential, a refresh power supply for setting the wiring to the second potential, the read power supply, and the refresh power supply. 4. The switch according to claim 1, wherein the first potential is a positive potential higher than the second potential. 5. A driving method of the photoelectric conversion device. The pulse driving method of a photoelectric conversion device according to any one of claims 1 to 3, characterized in that it is sequentially applied to a plurality of said drive lines.   The switch element includes the one electrode layer, the other electrode layer, an insulating layer provided between the one electrode layer and the other electrode layer, the insulating layer, and the other electrode layer. And a high-concentration impurity semiconductor layer provided between the semiconductor layer and the other electrode layer. A driving method of the photoelectric conversion device according to claim 1.   The method for driving a photoelectric conversion device according to claim 1, wherein the plurality of photoelectric conversion elements and the plurality of switch elements are provided on the same substrate.   8. The method for driving a photoelectric conversion device according to claim 1, further comprising detection means for detecting charges generated in the photoelectric conversion elements by the photoelectric conversion through the signal lines. 9. .