Photoelectric conversion panel, x-ray imaging panel, and method for controlling photoelectric conversion panel

Abstract

To provide a photoelectric conversion panel capable of reducing influence of a leakage current from a photodiode, an X-ray imaging panel, and a method for controlling the photoelectric conversion panel.SOLUTION: A photoelectric conversion panel 1 turns off a transistor Tr2 in a period in which a photodiode 21 is irradiated with light, turns on a transistor Tr1 in a state in which a transistor Tr3 is turned off to accumulate charges in a capacitive element 22, and turns on the transistor Tr2 in a state in which the transistor Tr1 is turned off in a readout period, thereby reading out the charges accumulated in the capacitive element 22; and turns on a transistor Tr3 in a state in which the transistor Tr1 is turned off in a period other than the period in which the photodiode 21 is irradiated with light, thereby continuously resetting the photodiode 21.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a photoelectric conversion panel, an X-ray imaging panel, and a method for controlling a photoelectric conversion panel. [Background technology]

[0002] Patent Document 1 discloses a radiation imaging device including a photodiode. The radiation imaging device performs a reset drive to reset the photodiode. Thereafter, the photodiode generates an electric charge according to the amount of radiation irradiated. Then, sampling drive is performed during the period in which radiation is irradiated. In the sampling drive, an operation is performed in which a signal according to the amount of electric charge generated in the photodiode is sampled and held in a capacitance. After the sampling drive, a reset drive is performed, and after the reset drive, a readout operation is performed. In the readout operation, the sampled signal is AD converted and output as one piece of image data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-10064 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a radiation imaging device (X-ray imaging device) such as that described in Patent Document 1, a small amount of light emitted from a scintillator during radiation irradiation (X-ray irradiation) enters a photodiode to which a reverse bias is applied, generating a current, which is then imaged. Here, in order to suppress the variation (unevenness) in the magnitude of the current generated in each photodiode, the photodiode is configured to suppress the recombination of residual carriers generated in the photodiode by photoexcitation.

[0005] However, the residual carriers (current) generated in the photodiode due to the incident light continue to leak from the photodiode even when the incident light from outside is no longer present (a leakage current occurs). For this reason, when X-ray moving images are generated by repeatedly capturing X-ray images, the leakage current causes an afterimage. Furthermore, when X-ray moving images are generated, since light continues to be incident continuously on the photodiode, the residual carriers continue to remain, causing a leakage current, and there is a problem that the afterimage is difficult to erase. In the radiation imaging device of Patent Document 1, a reset operation is performed for a certain period, such as before a readout operation, but this is not sufficient to reduce the influence of the leakage current from the photodiode.

[0006] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a photoelectric conversion panel, an X-ray imaging panel, and a control method for a photoelectric conversion panel that are capable of reducing the effects of leakage current from a photodiode. [Means for solving the problem]

[0007] In order to solve the above problem, a photoelectric conversion panel according to a first aspect of the present disclosure includes a first transistor, a photodiode connected to a first electrode which is one of a source electrode and a drain electrode of the first transistor, a capacitance element connected to a second electrode which is the other of the source electrode and the drain electrode of the first transistor, a second transistor connected to the first electrode, a third transistor connected to the second electrode, and a control circuit which transmits a control signal to each of the gate electrodes of the first transistor, the second transistor, and the third transistor, wherein the control circuit, during a period in which the photodiode is irradiated with light, blocks the second transistor and, with the third transistor blocked, causes the first transistor to be conductive to accumulate charge in the capacitance element, during a readout period in a period other than the period in which the photodiode is irradiated with light, reads out the charge accumulated in the capacitance element by causing the second transistor to be conductive with the first transistor blocked, and during a period other than the period in which the photodiode is irradiated with light, causes the third transistor to be conductive with the first transistor blocked, thereby continuously resetting the photodiode.

[0008] An X-ray imaging panel according to a second aspect includes the photoelectric conversion panel according to the first aspect, and a scintillator that converts X-rays into light and irradiates the light to the photodiode.

[0009] A control method for a photoelectric conversion panel according to a third aspect is a control method for a photoelectric conversion panel including a first transistor, a photodiode connected to a first electrode which is one of a source electrode and a drain electrode of the first transistor, a capacitive element connected to a second electrode which is the other of the source electrode and drain electrode of the first transistor, a second transistor connected to the first electrode, and a third transistor connected to the second electrode, wherein during a period in which the photodiode is irradiated with light, the second transistor is blocked and the first transistor is made conductive while the third transistor is blocked to accumulate charge in the capacitive element, during a readout period in a period other than the period in which the photodiode is irradiated with light, the second transistor is made conductive while the first transistor is blocked to read out the charge accumulated in the capacitive element, and during a period other than the period in which the photodiode is irradiated with light, the photodiode is continuously reset by making the third transistor conductive while the first transistor is blocked. Effect of the Invention

[0010] According to the above configuration, charges are accumulated in the capacitance element during a period in which the photodiode is irradiated with light. Then, during a readout period following the period in which light is irradiated, charges are read out from the capacitance element in a state in which the capacitance element and the photodiode are separated by the first transistor. This makes it possible to prevent the influence of leakage current from the photodiode when reading out charges from the capacitance element during the readout period. Then, since the photodiode is continuously reset during periods other than the period in which light is irradiated to the photodiode, leakage current in the photodiode that occurs during periods other than the period in which light is irradiated is erased. This makes it possible to reduce the influence of leakage current from the photodiode. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic diagram showing an X-ray imaging device 100 equipped with an X-ray imaging panel 10 including a photoelectric conversion panel 1 in this embodiment. [Diagram 2] FIG. 2 is a plan view showing a schematic configuration of the photovoltaic conversion panel 1. As shown in FIG. [Diagram 3] FIG. 3 is a circuit diagram showing the configuration of the sensor 12. As shown in FIG. [Figure 4] FIG. 4 is a timing chart showing the operation of the photoelectric conversion panel 1. As shown in FIG. [Diagram 5] FIG. 5 is a circuit diagram (1) for explaining the operation of the photovoltaic conversion panel 1. As shown in FIG. [Figure 6] FIG. 6 is a circuit diagram (2) for explaining the operation of the photoelectric conversion panel 1. In FIG. [Figure 7] FIG. 7 is a circuit diagram (3) for explaining the operation of the photoelectric conversion panel 1. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present disclosure will be described based on the drawings. Note that the present disclosure is not limited to the following embodiment, and appropriate design changes can be made within the scope of satisfying the configuration of the present disclosure. In addition, in the following description, the same parts or parts having similar functions are commonly used with the same reference numerals in different drawings, and repeated description thereof will be omitted. In addition, each configuration described in the embodiment and the modified example may be appropriately combined or changed within the scope of the gist of the present disclosure. In addition, in order to make the description easier to understand, in the drawings referred to below, the configuration is shown in a simplified or schematic manner, and some components are omitted. In addition, the dimensional ratio between the components shown in each figure does not necessarily indicate the actual dimensional ratio.

[0013] [Configuration of X-ray imaging device 100] 1 is a schematic diagram showing an X-ray imaging device 100 equipped with an X-ray imaging panel 10 including a photoelectric conversion panel 1 in this embodiment. The X-ray imaging device 100 includes the X-ray imaging panel 10 including the photoelectric conversion panel 1 and a scintillator 2, a control unit 3, and an X-ray source 4. The X-ray imaging device 100 is configured to repeatedly perform X-ray imaging and generate an X-ray video based on the captured images.

[0014] 1, the control unit 3 includes a scanning control circuit 3a, a signal readout circuit 3b, and a bias voltage supply circuit 3c. The control unit 3 includes a processor that executes control processing of the X-ray imaging device 100. The scanning control circuit 3a, the signal readout circuit 3b, and the bias voltage supply circuit 3c are each connected to the photoelectric conversion panel 1. In FIG. 1, the scanning control circuit 3a, the signal readout circuit 3b, and the bias voltage supply circuit 3c are depicted as separate blocks, but may be configured as an integrated circuit.

[0015] The X-ray source 4 irradiates the subject S with X-rays. The X-rays transmitted through the subject S are converted into fluorescence (hereinafter, scintillation light) in the scintillator 2 arranged on the upper part of the photoelectric conversion panel 1. The X-ray imaging device 100 generates an X-ray image by capturing the scintillation light on the X-ray imaging panel 10.

[0016] 2 is a schematic plan view showing a schematic configuration of the photoelectric conversion panel 1. On a substrate 11 of the photoelectric conversion panel 1, a plurality of sensors 12 are arranged in a matrix.

[0017] 3 is a circuit diagram showing a configuration of the sensor 12. The sensor 12 includes a photodiode 21, a capacitive element 22, and transistors Tr1 to Tr3. The photodiode 21 is, for example, a PIN type photodiode. The capacitive element 22 is a capacitor.

[0018] The semiconductor active layers of the transistors Tr1 to Tr3 are made of, for example, an amorphous oxide semiconductor containing indium (In), gallium (Ga) and zinc (Zn) in a predetermined ratio. The semiconductor active layers are not limited to this, and may be made of InGaO3 (ZnO)5, magnesium zinc oxide (Mg x Zinc 1-x O), cadmium zinc oxide (Cd x Zinc 1-x O), cadmium oxide (CdO), InSnZnO (containing In (indium), Sn (tin), and Zn (zinc)), In (indium)-Al (aluminum)-Zn (zinc)-O (oxygen)-based amorphous oxide semiconductors, etc. may also be used. In addition, "amorphous" and "crystalline (including polycrystalline, microcrystalline, and c-axis oriented)" materials are also applicable as oxide semiconductors.

[0019] The transistor Tr1 is disposed between the photodiode 21 and the capacitance element 22. The transistor Tr1 is disposed between the transistors Tr2 and Tr2. The cathode 21a of the photodiode 21 is connected to a bias voltage supply circuit 3c of the control unit 3 via a wiring. The bias voltage supply circuit 3c applies a bias voltage to the cathode 21a of the photodiode 21. The anode 21b of the photodiode 21 is connected to the transistors Tr1 and T3 via a node n1. One side of the capacitance element 22 is connected to the transistors Tr1 and T2 via a node n2. The other side of the capacitance element 22 is connected to a reference potential (for example, ground).

[0020] A gate electrode Tr1g of the transistor Tr1 is connected via a wiring to a scanning control circuit 3a of the control unit 3. The scanning control circuit 3a supplies a signal S1 to the gate electrode Tr1g of the transistor Tr1. A source electrode Tr1s of the transistor Tr1 is connected to a node n2. A drain electrode Tr1d of the transistor Tr1 is connected to the node n1. A gate electrode Tr1g of the transistor Tr1 is connected to the scanning control circuit 3a of the control unit 3 via a wiring. A source electrode Tr1s of the transistor Tr1 is connected to the node n2. A drain electrode Tr1d of the transistor Tr1 is connected to the node n1.

[0021] A gate electrode Tr2g of the transistor Tr2 is connected to a scanning control circuit 3a of the control unit 3 via a wiring. The scanning control circuit 3a supplies a signal S2 to the gate electrode Tr2g of the transistor Tr2. A source electrode Tr2s of the transistor Tr2 is connected to a signal read circuit 3b of the control unit 3 via a wiring. The signal read circuit 3b outputs a voltage Vd for reading out the amount of charge stored in the capacitive element 22 via the transistor Tr2. A drain electrode Tr2d of the transistor Tr2 is connected to a node n2. The voltage Vd is closer to the reference voltage than the voltage Vr.

[0022] A gate electrode Tr3g of the transistor Tr3 is connected to a scanning control circuit 3a of the control unit 3 via a wiring. The scanning control circuit 3a supplies a signal S3 to the gate electrode Tr3g of the transistor Tr3. A source electrode Tr3s of the transistor Tr3 is connected to a bias voltage supply circuit 3c of the control unit 3 via a wiring. The bias voltage supply circuit 3c applies a voltage Vr to the transistor Tr3 such that a voltage is applied to the photodiode 21 in the forward direction. A drain electrode Tr3d of the transistor Tr3 is connected to a node n1.

[0023] (Method of controlling photoelectric conversion panel 1) Next, a method for controlling the photoelectric conversion panel 1 will be described with reference to Fig. 4 to Fig. 7. Fig. 4 is a timing chart showing the operation of the photoelectric conversion panel 1. Figs. 5 to 7 are circuit diagrams for explaining the operation of the photoelectric conversion panel 1. The control process of the photoelectric conversion panel 1 is executed by the control unit 3.

[0024] <Period T1 before light exposure> As shown in FIG. 4, in a period T1 before a time t1 at which the photodiode 21 of the photoelectric conversion panel 1 is irradiated with light, the photodiode 21 is continuously reset. In this embodiment, "resetting" the photodiode 21 means applying a forward voltage to the photodiode 21 to remove remaining carriers. The voltage of the signal S1 is at a low level, the voltage of the signal S2 is at a low level, and the voltage of the signal S3 is at a high level. As a result, the transistor Tr1 shown in FIG. 3 is turned off (a state in which the source electrode Tr1s and the drain electrode Tr1d are disconnected), the transistor Tr2 is turned off, and the transistor Tr3 is turned on (a state in which the source electrode Tr3s and the drain electrode Tr3d are conductive). As a result, a forward voltage is applied to the photodiode 21.

[0025] <Period T2 during light incidence> As shown in Fig. 4, during a period T2 (the period from time t1 to time t2) when the photodiode 21 is irradiated with light, electric charges are accumulated in the capacitance element 22. As shown in Fig. 6, during the period T2, the transistors Tr2 and T3 are in an off state, and the transistor Tr1 is in an on state. As a result, electric charges are accumulated in the capacitance element 22 by a current flowing from the photodiode 21 irradiated with light.

[0026] <Read period T3> As shown in FIG. 4, in a readout period T3 (period from time t2 to time t3) after the period T2, the charge accumulated in the capacitance element 22 is read out. As shown in FIG. 7, in the period T3, the transistor Tr1 is in an off state, and the transistors Tr2 and T3 are in an on state. This causes the charge accumulated in the capacitance element 22 to be discharged from the capacitance element 22. Then, the signal readout circuit 3b reads a signal (voltage) corresponding to the charge discharged from the capacitance element 22, and the control unit 3 generates an image according to the signal. In addition, the photodiode 21 and the capacitance element 22 are in an electrically isolated state. As a result, when the charge is read out from the capacitance element 22, it is possible to prevent the influence of the leakage current from the photodiode 21 from occurring. In addition, in the readout period T3, the transistor Tr3 is in an on state, so that the photodiode 21 is reset. Note that, as shown in FIG. 4, the transistor Tr2 may be turned on at a time point after the time point t2.

[0027] <Read completion period T4> As shown in Fig. 4, in a read completion period T4 (the period from time t3 to time t4) following the read period T3, the transistor Tr2 is switched from on to off. This stops the readout of charges from the capacitance element 22. Also, as shown in Fig. 5, in the read completion period T4, the transistor Tr3 is on, so that the photodiode 21 is reset. Also, the transistor Tr1 is off, so that the photodiode 21 and the capacitance element 22 are separated from each other.

[0028] <Reset period T5 of the capacitive element 22> As shown in FIG. 4, in a reset period T5 (period from time t4 to time t5) of the capacitance element 22 after the read completion period T4, the capacitance element 22 is reset. The "reset" of the capacitance element 22 means that the potential difference between both ends of the capacitance element 22 is reduced to release the charge from the capacitance element 22. As shown in FIG. 7, in the period T5, the transistor Tr1 is in an off state, and the transistors Tr2 and T3 are in an on state. This releases the remaining charge from the capacitance element 22. In addition, the photodiode 21 is reset. As described above, the photodiode 21 is continuously reset during periods other than the period during which the photodiode 21 is irradiated with light, so that the leakage current in the photodiode 21 that occurs during periods other than the period during which the photodiode 21 is irradiated with light is erased. This makes it possible to reduce the influence of the leakage current from the photodiode 21. Note that, as shown in FIG. 4, the transistor Tr2 may be turned on at a time point later than time t4.

[0029] By controlling the operation of the photoelectric conversion panel 1 as described above, it is possible to reduce the influence of the leakage current from the photodiode 21. As a result, even when the X-ray imaging device 100 repeatedly performs X-ray imaging and generates an X-ray video based on the captured images, it is possible to prevent the occurrence of lags and ghosts.

[0030] [Variations] Although the embodiments have been described above, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure.

[0031] (1) In the above embodiment, the capacitive element 22 is reset during the period T5, but the present disclosure is not limited to this. For example, the capacitive element 22 may be reset during a period other than the period T2.

[0032] (2) In the above embodiment, the semiconductor material of the transistors Tr1 to Tr3 is an amorphous oxide semiconductor containing indium (In), gallium (Ga) and zinc (Zn) in a predetermined ratio, but the present disclosure is not limited to this. For example, the semiconductor material of the transistors Tr1 to Tr3 may be amorphous silicon (a-Si).

[0033] The above-mentioned photoelectric conversion panel, X-ray imaging panel, and method of controlling the photoelectric conversion panel 1 can also be explained as follows.

[0034] A photoelectric conversion panel according to a first configuration includes a first transistor, a photodiode connected to a first electrode which is one of a source electrode and a drain electrode of the first transistor, a capacitance element connected to a second electrode which is the other of the source electrode and the drain electrode of the first transistor, a second transistor connected to the first electrode, a third transistor connected to the second electrode, and a control circuit which transmits a control signal to each of the gate electrodes of the first transistor, the second transistor, and the third transistor, wherein the control circuit, during a period in which the photodiode is irradiated with light, blocks the second transistor and, with the third transistor blocked, causes the first transistor to be conductive to accumulate charge in the capacitance element, during a readout period in a period other than the period in which the photodiode is irradiated with light, reads out the charge accumulated in the capacitance element by making the second transistor conductive with the first transistor blocked, and during a period other than the period in which the photodiode is irradiated with light, causes the third transistor to be conductive with the first transistor blocked, thereby continuously resetting the photodiode (first configuration).

[0035] According to the first configuration, charges are accumulated in the capacitance element during a period in which the photodiode is irradiated with light. Then, during a readout period following the period in which light is irradiated, charges are read out from the capacitance element in a state in which the capacitance element and the photodiode are separated by the first transistor. This makes it possible to prevent the occurrence of an influence of a leakage current from the photodiode when reading out charges from the capacitance element during the readout period. Then, since the photodiode is continuously reset during periods other than the period in which light is irradiated to the photodiode, a leakage current in the photodiode that occurs during periods other than the period in which light is irradiated is erased. This makes it possible to reduce an influence of a leakage current from the photodiode.

[0036] In the first configuration, the control circuit may be configured to reset the capacitive element by turning on the second transistor while turning off the first transistor after the readout period (second configuration).

[0037] According to the second configuration, the capacitance element can be reset, so that it is possible to prevent unnecessary charges from remaining in the capacitance element, which may cause noise.

[0038] An X-ray imaging panel according to a third configuration includes the photoelectric conversion panel according to the first or second configuration, and a scintillator that converts X-rays into light and irradiates the light to the photodiode.

[0039] According to the third configuration, since the photoelectric conversion panel according to the first or second configuration is included, it is possible to provide an X-ray imaging panel capable of reducing the influence of leakage current from the photodiode.

[0040] A control method for a photoelectric conversion panel according to a fourth configuration is a control method for a photoelectric conversion panel including a first transistor, a photodiode connected to a first electrode which is one of a source electrode and a drain electrode of the first transistor, a capacitance element connected to a second electrode which is the other of the source electrode and drain electrode of the first transistor, a second transistor connected to the first electrode, and a third transistor connected to the second electrode, wherein during a period in which the photodiode is irradiated with light, the second transistor is blocked and the first transistor is made conductive while the third transistor is blocked to accumulate charge in the capacitance element, during a readout period in a period other than the period in which the photodiode is irradiated with light, the second transistor is made conductive while the first transistor is blocked to read out the charge accumulated in the capacitance element, and during a period other than the period in which the photodiode is irradiated with light, the photodiode is continuously reset by making the third transistor conductive while the first transistor is blocked (fourth configuration). [Explanation of symbols]

[0041] 1: photoelectric conversion panel, 2: scintillator, 3: control unit, 3a: scanning control circuit, 3b: signal readout circuit, 3c: bias voltage supply circuit, 4: X-ray source, 10: X-ray imaging panel, 11: substrate, 12: sensor, 21: photodiode, 21a: cathode, 21b: anode, 22: capacitance element, 100: X-ray imaging device, S: subject, Tr1: transistor, Tr2: transistor, Tr3: transistor

Claims

1. A first transistor; a photodiode connected to a first electrode, which is one of a source electrode and a drain electrode of the first transistor; a capacitance element connected to a second electrode, which is the other of the source electrode and the drain electrode of the first transistor; a second transistor connected to the first electrode; a third transistor connected to the second electrode; a control circuit that transmits a control signal to a gate electrode of each of the first transistor, the second transistor, and the third transistor; The control circuit includes: during a period in which the photodiode is irradiated with light, the second transistor is turned off and the third transistor is turned off, and the first transistor is turned on to accumulate charge in the capacitance element; during a readout period other than a period during which the photodiode is irradiated with light, the second transistor is made conductive while the first transistor is made non-conductive, thereby reading out the charge stored in the capacitance element; a photoelectric conversion panel in which the photodiode is continuously reset by causing the third transistor to conduct while causing the first transistor to be cut off during a period other than a period in which the photodiode is irradiated with light.

2. 2 . The photoelectric conversion panel according to claim 1 , wherein the control circuit resets the capacitance element by turning on the second transistor while turning off the first transistor after the readout period.

3. The photoelectric conversion panel according to claim 1 or 2; and a scintillator that converts X-rays into light and irradiates the photodiode with the light.

4. A first transistor; a photodiode connected to a first electrode, which is one of a source electrode and a drain electrode of the first transistor; a capacitance element connected to a second electrode, which is the other of the source electrode and the drain electrode of the first transistor; a second transistor connected to the first electrode; a third transistor connected to the second electrode, during a period in which the photodiode is irradiated with light, the second transistor is turned off and the third transistor is turned off, and the first transistor is turned on to accumulate charge in the capacitance element; during a readout period other than a period during which the photodiode is irradiated with light, the second transistor is made conductive while the first transistor is made non-conductive, thereby reading out the charge stored in the capacitance element; A method for controlling a photoelectric conversion panel, comprising the steps of: resetting the photodiode continuously by turning on the third transistor while turning off the first transistor during a period other than a period during which the photodiode is irradiated with light.

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