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

Abstract

Provided are a photoelectric conversion panel, an X-ray imaging panel, and a method for controlling the photoelectric conversion panel, with which it is possible to reduce the influence of a leakage current from a photodiode. The photoelectric conversion panel (1) causes the capacitor element (22) to accumulate charge by turning on the transistor (Tr1) in a state in which the transistor (Tr2) is turned off and the transistor (Tr3) is turned off during a period in which the photodiode (21) is irradiated with light, and reads out the charge accumulated in the capacitor element (22) by turning on the transistor (Tr2) in a state in which the transistor (Tr1) is turned off during a read-out period in which the photoelectric conversion panel (1) reads out the charge accumulated in the capacitor element (22) by turning on the transistor (Tr2) in a state in which the transistor (Tr1) is turned off. The photodiode (21) is continuously reset by turning on the transistor (Tr3) in a state in which the transistor (Tr1) is turned off during a period other than a period in which the photodiode (21) is irradiated with light.

Description

Technical Field

[0001] The present disclosure relates to a photoelectric conversion panel, an X-ray imaging panel, and a control method of the photoelectric conversion panel. Background Art

[0002] Patent document 1 discloses a radiographic device including a photodiode. The radiographic device performs a reset drive to reset the photodiode. Thereafter, the photodiode generates a charge corresponding to the amount of radiation irradiated. Then, a sampling drive is performed during the period of irradiation of the radiation. In the sampling drive, an action is performed to sample a signal corresponding to the amount of charge generated in the photodiode and hold it in a capacitor. After the sampling drive, a reset drive is performed, and after the reset drive, a readout action is performed. In the readout action, the sampling signal is A / D converted and output as a single image data. Prior art literature Patent Literature

[0003] Patent Document 1: Japanese Patent Application Publication No. 2016-10064 Summary of the invention Problems to be solved by the invention

[0004] In the radiographic device (X-ray imaging device) described in Patent Document 1, when radiation is irradiated (X-ray irradiation is performed), a tiny light emitted from a scintillator enters a photodiode to which a reverse bias is applied, thereby generating a current, which is imaged. Here, in order to suppress the deviation (unevenness) of the magnitude of the current generated in each photodiode, the photodiode is configured to suppress the recombination of residual carriers generated by light excitation in the photodiode.

[0005] However, the residual carriers (current) generated in the photodiode due to incident light continue to leak from the photodiode (generating leakage current) even in the absence of incident light from the outside. Therefore, when generating an X-ray dynamic image by repeatedly taking X-ray images, an afterimage is generated due to the above leakage current. In addition, when generating an X-ray motion image, since light continues to be incident on the photodiode, residual carriers continue to remain, generating leakage current, and there is a problem that the afterimage is difficult to eliminate. In the radiation imaging device of the above-mentioned patent document 1, although a reset action is performed in a temporary period such as before the readout action, it is not enough 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 an object of the present disclosure is to provide a photoelectric conversion panel, an X-ray imaging panel, and a control method of a photoelectric conversion panel that can reduce the influence of leakage current from a photodiode. Solutions to Solve Problems

[0007] In order to solve the above-mentioned problems, the photoelectric conversion panel involved in the first mode of the present disclosure comprises: a first transistor; a photodiode connected to a first electrode which is one of the source electrode and the drain electrode of the first transistor; a capacitor 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 sends a control signal to the gate electrodes of each of the first transistor, the second transistor and the third transistor, wherein the control circuit turns on the first transistor and accumulates charge in the capacitor while the second transistor is turned off and the third transistor is turned off during a period when the photodiode is irradiated with light, and during a readout period other than the period when the photodiode is irradiated with light, the second transistor is turned on while the first transistor is turned off, thereby reading out the charge accumulated in the capacitor, and during a period other than the period when the photodiode is irradiated with light, the third transistor is turned on while the first transistor is turned off, 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 photodiode with the light.

[0009] In the control method of the photoelectric conversion panel involved in the third aspect, the photoelectric conversion panel comprises: a first transistor; a photodiode connected to a first electrode which is one of the source electrode and the drain electrode of the first transistor; a capacitor 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; and a third transistor connected to the second electrode. During the period when the photodiode is irradiated with light, the first transistor is turned on and the capacitor accumulates charge in a state where the second transistor is turned off and the third transistor is turned off; during a readout period in a period other than the period when the photodiode is irradiated with light, the second transistor is turned on in a state where the first transistor is turned off, thereby reading out the charge accumulated in the capacitor; during the period other than the period when the photodiode is irradiated with light, the third transistor is turned on in a state where the first transistor is turned off, thereby continuously resetting the photodiode. Effects of the Invention

[0010] According to the above-mentioned configuration, during the period when the photodiode is irradiated with light, charge is accumulated in the capacitor element. Then, during the readout period after the period of irradiation with light, the charge is read out from the capacitor element in a state where the capacitor element and the photodiode are separated by the first transistor. Thus, during the readout period, when the charge is read out from the capacitor element, the influence caused by the leakage current from the photodiode can be prevented. Then, during the period other than the period when the photodiode is irradiated with light, the photodiode is continuously reset, so that the leakage current in the photodiode generated during the period other than the period when the photodiode is irradiated with light is eliminated. Thus, the influence caused by the leakage current from the photodiode can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a schematic diagram showing an X-ray imaging device 100 including an X-ray imaging panel 10 of the photoelectric conversion panel 1 in the present embodiment. Figure 2 It is a schematic plan view showing a schematic structure of the photoelectric conversion panel 1 . Figure 3 : is a circuit diagram showing the structure of the sensor 12. Figure 4 1 is a timing chart showing the operation of the photoelectric conversion panel 1 . Figure 5 This is a circuit diagram (1) for explaining the operation of the photoelectric conversion panel 1. Figure 6 This is a circuit diagram (2) for explaining the operation of the photoelectric conversion panel 1. Figure 7 This is a circuit diagram (3) for explaining the operation of the photoelectric conversion panel 1. DETAILED DESCRIPTION

[0012] Hereinafter, an embodiment of the present disclosure will be described based on the accompanying drawings. In addition, the present disclosure is not limited to the following embodiments, and design changes can be appropriately made within the scope of the configuration of the present disclosure. In addition, in the following description, for the same parts or parts with the same functions, the same figure marks are used in common between different drawings, and their repeated descriptions are omitted. In addition, the various structures described in the embodiments and modified examples can be appropriately combined or changed without departing from the main purpose of the present disclosure. In addition, in order to facilitate the understanding of the description, in the drawings referred to below, the structure is simplified or schematically shown, or a part of the constituent components is omitted. In addition, the size ratios between the constituent components shown in the various figures do not necessarily represent the actual size ratios.

[0013] [Structure of X-ray Imaging Device 100] Figure 11 is a schematic diagram showing an X-ray imaging device 100 having an X-ray imaging panel 10 including a photoelectric conversion panel 1 in the present embodiment. The X-ray imaging device 100 includes: an X-ray imaging panel 10 including a 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 dynamic image based on the captured images.

[0014] like Figure 1 As shown in FIG. 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 performs 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 connected to the photoelectric conversion panel 1, respectively. Figure 1 In FIG. 1 , the scanning control circuit 3 a , the signal reading circuit 3 b , and the bias voltage supply circuit 3 c are described as separate modules, but they 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 referred to as scintillation light) by the scintillator 2 disposed on the upper portion of the photoelectric conversion panel 1. The X-ray imaging device 100 generates an X-ray image by capturing scintillation light on the X-ray imaging panel 10.

[0016] Figure 2 1 is a schematic plan view showing a schematic structure 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] Figure 3 2 is a circuit diagram showing the structure of the sensor 12. The sensor 12 includes a photodiode 21, a capacitor 22, and transistors Tr1 to Tr3. The photodiode 21 is, for example, a PIN-type photodiode. The capacitor 22 is a capacitor.

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

[0019] The transistor Tr1 is arranged between the photodiode 21 and the capacitor 22. In addition, the transistor Tr1 is arranged between the transistor Tr2 and the transistor Tr3. The cathode 21a of the photodiode 21 is connected to the bias voltage supply circuit 3c of the control unit 3 via 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 transistor Tr1 and T3 via the node n1. One side of the capacitor 22 is connected to the transistor Tr1 and T2 via the node n2. The other side of the capacitor 22 is connected to a reference potential (for example, ground).

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

[0021] The gate electrode Tr2g of the transistor Tr2 is connected to the scanning control circuit 3a of the control unit 3 via wiring. The scanning control circuit 3a supplies the signal S2 to the gate electrode Tr2g of the transistor Tr2. The source electrode Tr2s of the transistor Tr2 is connected to the signal readout circuit 3b of the control unit 3 via wiring. The signal readout circuit 3b outputs a voltage Vd for reading the size of the charge accumulated in the capacitor 22 via the transistor Tr2. The drain electrode Tr2d of the transistor Tr2 is connected to the node n2. The voltage Vd is a voltage having a value closer to the reference voltage than the voltage Vr.

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

[0023] (Control Method of Photoelectric Conversion Panel 1) Next, refer to Figures 4 to 7 A method of controlling the photoelectric conversion panel 1 will be described. Figure 4 1 is a timing chart showing the operation of the photoelectric conversion panel 1 . Figure 5 to Figure 72 is a circuit diagram 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 irradiation> like Figure 4 As shown, during the period T1 before the moment t1 at which the photodiode 21 of the photoelectric conversion panel 1 is irradiated with light, the photodiode 21 is continuously reset. The "reset" of the photodiode 21 means that, in this embodiment, a positive voltage is applied to the photodiode 21 to remove residual 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. Thus, Figure 3 The transistor Tr1 shown is turned off (the source electrode Tr1s and the drain electrode Tr1d are turned off), the transistor Tr2 is turned off, and the transistor Tr3 is turned on (the source electrode Tr3s and the drain electrode Tr3d are turned on). As a result, a forward voltage is applied to the photodiode 21 .

[0025] <Light incident period T2> like Figure 4 As shown, during the period T2 (the period from time t1 to time t2) when the photodiode 21 is irradiated with light, electric charge is accumulated in the capacitor 22. Figure 6 As shown, in the period T2, the transistors Tr2 and Tr3 are in the off state, and the transistor Tr1 is in the on state. Thus, the electric charge is accumulated in the capacitor 22 by the current flowing from the photodiode 21 irradiated with light.

[0026] <Reading period T3> like Figure 4 As shown, in the readout period T3 (the period from time t2 to time t3) after the period T2, the charge accumulated in the capacitor element 22 is read out. Figure 7 As shown, during the period T3, the transistor Tr1 is in the off state, and the transistors Tr2 and T3 are in the on state. As a result, the charge accumulated in the capacitor 22 is discharged from the capacitor 22. Then, the signal readout circuit 3b reads the signal (voltage) corresponding to the charge discharged from the capacitor 22, and the control unit 3 generates an image based on the signal. In addition, the photodiode 21 and the capacitor 22 are electrically separated. As a result, when the charge is read out from the capacitor 22, the influence caused by the leakage current from the photodiode 21 can be prevented. In addition, during the readout period T3, the photodiode 21 is reset by the transistor Tr3 being in the on state. In addition, as Figure 4 As shown, the transistor Tr2 may be turned on at a time point after the time t2.

[0027] <Readout completion period T4> like Figure 4 As shown in FIG. 1 , in the read completion period T4 (the period from time t3 to time t4) after the read period T3, the transistor Tr2 is switched from on to off. Thus, the charge reading from the capacitor element 22 is stopped. Figure 5 As shown, in the readout completion period T4, the transistor Tr3 is in the on state, and the photodiode 21 is reset. In addition, the photodiode 21 and the capacitor 22 are separated by the transistor Tr1 being in the off state.

[0028] <<Reset Period T5 of Capacitor Element 22> like Figure 4 As shown in FIG. 1 , during the reset period T5 (the period from time t4 to time t5) of the capacitor 22 after the readout completion period T4, the capacitor 22 is reset. The “reset” of the capacitor 22 means that the charge is discharged from the capacitor 22 by reducing the potential difference between the two ends of the capacitor 22. Figure 7 As shown, during period T5, transistor Tr1 is in the off state, and transistors Tr2 and Tr3 are in the on state. As a result, the residual charge is discharged from the capacitor 22. In addition, the photodiode 21 is reset. As described above, the photodiode 21 is continuously reset during the period other than the period when the photodiode 21 is irradiated with light, so the leakage current in the photodiode 21 generated during the period other than the light irradiation period is eliminated. As a result, the influence caused by the leakage current from the photodiode 21 can be reduced. In addition, if Figure 4 As shown, the transistor Tr2 may be turned on at a time point after the 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 X-ray dynamic images based on the captured images, it is possible to prevent the occurrence of lag and ghost.

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

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

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

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

[0034] The photoelectric conversion panel involved in the first structure comprises: a first transistor; a photodiode, which is connected to a first electrode which is one of the source electrode and the drain electrode of the first transistor; a capacitor, which is connected to a second electrode which is the other of the source electrode and the drain electrode of the first transistor; a second transistor, which is connected to the first electrode; a third transistor, which is connected to the second electrode; and a control circuit, which sends a control signal to the gate electrodes of each of the first transistor, the second transistor and the third transistor, wherein the control circuit turns on the first transistor and accumulates charge in the capacitor while the second transistor is turned off and the third transistor is turned off during the period when the photodiode is irradiated with light; during a readout period in a period other than the period when the photodiode is irradiated with light, the second transistor is turned on while the first transistor is turned off, thereby reading out the charge accumulated in the capacitor; during a period other than the period when the photodiode is irradiated with light, the third transistor is turned on while the first transistor is turned off, thereby continuously resetting the photodiode (first structure).

[0035] According to the first structure, during the period when the photodiode is irradiated with light, charge is accumulated in the capacitor. Then, during the readout period after the period of irradiation with light, the charge is read out from the capacitor in a state where the capacitor and the photodiode are separated by the first transistor. Thus, it is possible to prevent the influence caused by the leakage current from the photodiode when the charge is read out from the capacitor during the readout period. Then, during the period other than the period when the photodiode is irradiated with light, the photodiode is continuously reset, so that the leakage current in the photodiode generated during the period other than the period when the photodiode is irradiated with light is eliminated. Thus, it is possible to reduce the influence caused by the leakage current from the photodiode.

[0036] In the first configuration, the control circuit may be configured to, after the read period, turn on the second transistor in a state where the first transistor is turned off, thereby resetting the capacitor (second configuration).

[0037] According to the second configuration, since the capacitor element can be reset, it is possible to prevent unnecessary charge in the capacitor element which may cause noise from remaining.

[0038] The X-ray imaging panel according to the 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 photodiode with the light.

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

[0040] In the control method of the photoelectric conversion panel involved in the fourth structure, the photoelectric conversion panel includes: a first transistor; a photodiode connected to a first electrode which is one of the source electrode and the drain electrode of the first transistor; a capacitor 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; and a third transistor connected to the second electrode. The control method of the photoelectric conversion panel is characterized in that, during a period when the photodiode is irradiated with light, the first transistor is turned on and the capacitor accumulates charge in a state where the second transistor is turned off and the third transistor is turned off; during a readout period in a period other than the period when the photodiode is irradiated with light, the second transistor is turned on in a state where the first transistor is turned off, thereby reading out the charge accumulated in the capacitor; during a period other than the period when the photodiode is irradiated with light, the third transistor is turned on in a state where the first transistor is turned off, thereby continuously resetting the photodiode (fourth structure). Description of Reference Numerals

[0041] 1: Photoelectric conversion panel 2: Flasher 3: Control Department 3a: Scan control circuit 3b: Signal readout circuit 3c: Bias voltage supply circuit 4: X-ray source 10: X-ray camera panel 11: Substrate 12: Sensor 21: Photodiode 21a: cathode 21b: Anode 22: Capacitor element 100: X-ray camera S: Subject Tr1: Transistor Tr2: Transistor Tr3: Transistor

Claims

1. A photoelectric conversion panel, characterized in that: have: 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 capacitor 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; as well as a control circuit that sends a control signal to the gate electrodes of the first transistor, the second transistor, and the third transistor, respectively; The control circuit performs the following control operations: During a period when the photodiode is irradiated with light, in a state where the second transistor is turned off and the third transistor is turned off, the first transistor is turned on to accumulate charge in the capacitor; During a readout period other than a period during which the photodiode is irradiated with light, the second transistor is turned on while the first transistor is turned off, thereby reading out the charge accumulated in the capacitor; During a period other than a period during which the photodiode is irradiated with light, the photodiode is continuously reset by turning on the third transistor in a state in which the first transistor is turned off.

2. The photoelectric conversion panel according to claim 1, characterized in that: After the read period, the control circuit turns on the second transistor in a state where the first transistor is turned off, thereby resetting the capacitor.

3. An X-ray imaging panel, characterized in that: have: The photoelectric conversion panel according to claim 1 or 2; and The scintillator converts the X-rays into light and irradiates the light to the photodiode.

4. A method for controlling a photoelectric conversion panel, the photoelectric conversion panel comprising: 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 capacitor 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; as well as A third transistor is connected to the second electrode, and the control method of the photoelectric conversion panel is characterized in that: During a period when the photodiode is irradiated with light, in a state where the second transistor is turned off and the third transistor is turned off, the first transistor is turned on and the capacitor accumulates charge; During a readout period other than a period during which the photodiode is irradiated with light, the second transistor is turned on while the first transistor is turned off, thereby reading out the charge accumulated in the capacitor; During a period other than a period during which the photodiode is irradiated with light, the photodiode is continuously reset by turning on the third transistor in a state in which the first transistor is turned off.

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