Method for actuating radiation imaging apparatus and radiation imaging apparatus

Abstract

To provide a method for actuating a radiation imaging apparatus for determining the characteristics of a switching element in the apparatus, and to provide the radiation imaging apparatus.SOLUTION: A radiation imaging apparatus comprises: a plurality of pixels 100 each including a conversion element 102 that converts radiation or light into electric charges and accumulates the electric charges, and a switching element 101 that reads out an electric signal according to the electric charges from the conversion element; a bias power supply 103 that supplies bias potential to the conversion elements through bias lines Bs; a drive circuit 114 that supplies control signals to control electrodes of the switching elements through drive lines Vg(k) to control the switching elements; a read-out circuit 113 that reads out electric signals from the switching elements through signal lines Sig(j); an electric charge measurement unit that measures the amount of electric charges based on a current flowing in any one of the signal lines, the bias lines, and the drive lines; and a control operation unit. The electric charge measurement unit measures the amount of electric charges of the switching elements during a transition from a non-conduction state to a conduction state. The control operation unit determines the characteristics of the switching elements on the basis of the measured amount of electric charges.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for operating a radiation imaging device and to a radiation imaging device. [Background technology]

[0002] There is a radiation imaging device in which a scintillator, driver circuit, etc. are arranged on a sensor substrate on which pixels, each having a photoelectric conversion element such as a PIN diode and a switching element such as a thin-film transistor (TFT), are formed in a two-dimensional matrix. Such radiation imaging devices are used not only for medical purposes such as diagnostic imaging, but also for industrial purposes such as electronic component inspection and piping inspection. Since high resolution and a high frame rate are required for electronic component inspection applications, it is recommended to use oxide TFTs, which use an oxide semiconductor in the channel layer.

[0003] When a radiation imaging device is used for a long period of time, the threshold voltage of the switch element may fluctuate due to the influence of the voltage applied to the switch element, X-rays irradiated to the switch element, etc., and the quality of the captured image may deteriorate. Patent Document 1 discloses a method for measuring the threshold voltage of the switch element in the radiation imaging device as a means for detecting such deterioration in quality and the resulting lifespan of the radiation imaging device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-95507 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires that in addition to the conductive potential, at least two or more different non-conductive potentials be supplied to the control electrode of the switch element, and that the bias power supply be capable of supplying multiple potentials. This makes the device configuration complicated. Furthermore, it is necessary to wait for the leakage current of the switch element to stabilize, which can make measurement time-consuming.

[0006] An object of the present invention is to provide a technique that is advantageous for determining the characteristics of a switching element in a radiation imaging apparatus. [Means for solving the problem]

[0007] In order to solve the above problem, the present invention provides a method for operating a radiation imaging apparatus comprising: a plurality of pixels each including a conversion element that converts radiation or light into an electric charge and stores the electric charge; and a switch element that reads out an electric signal corresponding to the electric charge from the conversion element; a bias power supply that supplies a bias potential to the conversion element via a bias line; a drive circuit that controls the switch element by supplying a control signal to a control electrode of the switch element via a drive line; a readout circuit that reads out an electric signal from the switch element via a signal line; a charge measurement unit that measures an amount of electric charge based on a current flowing through any one of the signal line, the bias line, and the drive line; and a control and calculation unit, the method comprising: a measurement step of measuring the amount of electric charge by the charge measurement unit while the switch element transitions from a non-conductive state to a conductive state; and a determination step of determining characteristics of the switch element based on the amount of electric charge measured by the control and calculation unit. [Effects of the Invention]

[0008] It is possible to provide a technique that is advantageous for determining the characteristics of a switching element in a radiation imaging apparatus. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a radiation imaging system according to a first embodiment. [Figure 2]2 is a part of a circuit diagram of the radiation imaging apparatus of the first embodiment. [Figure 3] 3A to 3C are diagrams illustrating an operation method of the first embodiment. [Figure 4] FIG. 3 is a diagram illustrating the measurement operation of the first embodiment. [Figure 5] FIG. 10 is a diagram illustrating an operation method of a modified example of the first embodiment. [Figure 6] FIG. 3 is a diagram illustrating the measurement operation of the first embodiment. [Figure 7] 10 is a part of a circuit diagram of a radiation imaging apparatus according to a second embodiment. [Figure 8] FIG. 10 is a diagram illustrating the measurement operation of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0011] Example 1 A radiation imaging system for inspecting electronic components to which the present invention can be applied will be described with reference to FIG. 1. The radiation generating device can irradiate radiation downward (in the -z direction) in the figure. The movable stage carrying the object to be inspected (subject) and the movable stage carrying the radiation imaging device each move within the xy plane, while the radiation imaging device continuously acquires images. The radiation control device can supply the radiation generating device with a high voltage required for radiation generation and signals to control the generation and stopping of radiation. The radiation imaging system may also include a computer. The computer controls the radiation control device, the movable stage, and the radiation imaging device. The computer can also cause the radiation imaging device to perform various operations, such as imaging, measuring threshold voltages (described below), and determining the characteristics of switching elements.

[0012] The radiation imaging device includes a sensor substrate that detects radiation, a readout circuit that reads out charge information from the sensor substrate, a drive circuit that controls the drive of the sensor substrate, and a power supply unit that supplies voltage to these. The radiation imaging device also includes a charge measurement unit that is used to measure the threshold voltage of the switching element for each pixel or each region. The charge measurement unit may be a dedicated unit, or another element in the radiation imaging device may also function as the charge measurement unit.

[0013] In this embodiment, the readout circuit can function as the charge measurement unit. The radiation imaging device can also include a control and calculation unit that controls the sensor substrate, readout circuit, drive circuit, and power supply unit. The control and calculation unit can control the transition between processes, such as the threshold voltage measurement operation described below, and control the functions of the radiation imaging device. The control and calculation unit can also form a two-dimensional image based on output information from the readout circuit. The radiation imaging device can further include a memory.

[0014] The radiation imaging device will be described with reference to FIG. 2. The radiation imaging device has a drive circuit 114, a sensor substrate 112, a bias power supply 103, and a readout circuit 113. In this embodiment, the readout circuit 113 can function as a charge measurement unit. The radiation imaging device may further have an output buffer amplifier 109, an analog-to-digital (A / D) converter 110, and a control and calculation unit. The control and calculation unit can process the output of the A / D converter 110 to generate an image signal and determine the characteristics of the pixel switch elements. The sensor substrate 112 is a sensor in which radiation-detecting pixels 100 are arranged in a two-dimensional matrix of multiple rows and multiple columns.

[0015] For ease of explanation, FIG. 2 shows only some of the pixels 100 on the sensor substrate 112, but an actual sensor substrate may have many more pixels; for example, in the case of a 17×17 inch sensor, the sensor substrate may have approximately 2800 rows and approximately 2800 columns of pixels. Each pixel 100 has a conversion element 102 that converts radiation or light into an electric charge, and a switch element 101 that outputs an electric signal corresponding to the charge of the conversion element. The switch element 101 is a transistor such as a TFT, and has a gate electrode 101b, a source electrode 101c, a drain electrode 101a, and a channel layer (not shown). From the viewpoint of increasing the speed and resolution of radiation imaging devices, it is preferable to use an oxide semiconductor, for example, an amorphous oxide semiconductor such as IGZO or IZO, for the channel layer.

[0016] The conversion element 102 is either an indirect or direct conversion element, and converts irradiated radiation into electric charges. An indirect conversion element includes a wavelength converter that converts radiation into light and a photoelectric conversion element that converts the light into electric charges. A direct conversion element directly converts radiation into electric charges. In this embodiment, a PIN-type diode primarily made of amorphous silicon (a-Si) is used as the indirect conversion element. The conversion element 102 includes an individual electrode 102a, a common electrode 102c, and a photoelectric conversion layer 102b sandwiched between them and primarily made of a-Si. The photoelectric conversion layer 102b is a PIN-type diode in which the side closer to the individual electrode 102a is n+ type and the side closer to the common electrode 102c is p+ type. The individual electrode 102a is connected to the source electrode 101c of the switch element 101, and the common electrode 102c is electrically connected to the bias power supply 103 via a common bias line Bs.

[0017] In this embodiment, the bias line Bs extends in the column direction, but it may also extend in the row direction. The gate electrodes 102b of each switch element of the pixels in the kth row (shown as k = 0 to Y-1) are commonly connected to a drive line Vg(k). The drain electrodes 101a of each switch element of the pixels in the jth column (shown as j = 0 to X-1) are commonly connected to a signal line Sig(j) provided for each column, and the source electrodes 101c of each switch element are respectively connected to the individual electrodes 102c of the conversion elements of each pixel.

[0018] The drive lines Vg provided in each row are connected to the control electrodes of the switch elements in that row. The drive circuit 114 is, for example, a shift register, and controls the conduction state of the switch elements 101 by supplying control signals to the switch elements 101 via the drive lines Vg(0), Vg(1), . . .

[0019] The readout circuit 113 is provided with an amplifier circuit 106 for each signal line Sig, which amplifies the electrical signal on each signal line Sig. Each amplifier circuit 106 has an integrating amplifier 105, a variable gain amplifier 104, and a sample-and-hold circuit 107. The integrating amplifier 105 amplifies the electrical signal on the signal line. The variable gain amplifier 104 amplifies the electrical signal from the integrating amplifier 105 with a variable gain. The sample-and-hold circuit 107 samples and holds the electrical signal amplified by the variable gain amplifier 104.

[0020] The integrating amplifier 105 includes an operational amplifier 121 that amplifies and outputs the electrical signal on the signal line, an integrating capacitor 122, and a reset switch 123. The integrating amplifier 105 can change its gain (amplification factor) by changing the value of the integrating capacitor 122.

[0021] The integrating amplifier 105 can integrate the input current for a predetermined period and output it as a voltage signal. As a result, the integrating amplifier 105 can integrate the current flowing into the integrating amplifier 105 while the drive line potential Vg transitions from Voff to Von and output a voltage signal. Since the integrated value of the current is the amount of charge, the amount of charge based on the current input to the integrating amplifier 105 can be measured from the output voltage of the integrating amplifier 105.

[0022] The readout circuit 113 also has a switch 126 for each column and a multiplexer 108. The multiplexer 108 sequentially turns on the switches 126 for each column, thereby sequentially outputting the electrical signals output in parallel from the amplifier circuits 106 to an output buffer amplifier 109 as serial signals. The output buffer amplifier 109 performs impedance conversion on the electrical signals and outputs them. An analog-to-digital (A / D) converter 110 converts the analog electrical signals output from the output buffer amplifier 109 into digital electrical signals and outputs them to the control and calculation unit.

[0023] The drive circuit 114 outputs a control signal having a conductive potential Von that turns the switch element into a conductive state and a non-conductive potential Voff that turns the switch element into a non-conductive state to each of the drive lines Vg(0), Vg(1), . . .

[0024] The power supply unit supplies a reference potential Vref to the non-inverting input terminal of each operational amplifier, a bias potential Vs to the bias power supply 103, and a conductive potential Von and a non-conductive potential Voff to the drive circuit. The bias potential Vs is set to be a sufficiently negative potential with respect to the reference potential Vref (for example, Vs-Vref=-2 to -10V) in order to apply a reverse bias to the conversion element 102 and sufficiently deplete the photoelectric conversion layer 102b to perform photoelectric conversion.

[0025] The conduction potential Von is a sufficiently large positive potential (Von-Vref=+20 to +5V) that puts the switch element into a completely conductive state, allowing for rapid signal charge transfer from the conversion element. The non-conduction potential Voff controls the switch element so that it is completely non-conductive. In other words, Voff is a sufficiently large negative potential (Voff-Vref=-5 to -20V) that makes the drain-source leakage current in the switch element negligibly small (10^-14 A or less).

[0026] 3(a) and 3(b) show a flowchart and a timing chart of the operation S100 of measuring the threshold voltage of each pixel in the radiation imaging apparatus. The radiation imaging apparatus is controlled by an operation method including the following steps shown in FIG. Reset step S001: The drive lines Vg are sequentially set to the conductive potential Von, and unnecessary charges (such as dark charges due to dark currents in the conversion elements) accumulated in the conversion elements 102 are discharged to the readout circuit 113 to reset the conversion elements.

[0027] First step S002: The drive line potential Vg(0) for row 0 is set to the non-conducting potential Voff, and the switch element for row 0 is set to the non-conducting state. In the readout circuit 113, the integrating amplifier 105 measures the amount of charge N based on the current flowing through the signal line for each column. The output of the integrating amplifier 105 is input to the sample-and-hold circuit 107 via the variable gain amplifier 104 of the readout circuit 113. The sample-and-hold circuit 107 samples the output of the integrating amplifier 105 at the timing indicated by "N" in FIG. 3(b). The sampled and held voltage is read out via a multiplexer and output as digital data from the A / D converter 110. This digital data is a value corresponding to the amount of charge N. In this embodiment, the data obtained by A / D conversion of the integrated and sampled and held voltage is used as the amount of charge. The amount of charge N measured in this manner is obtained by integrating the current flowing through each signal line during this process until the current settles down.

[0028] Second step S003: The potential of the drive line in row 0 is set to the conductive potential Von, and the switch element in row 0 is set to the conductive state. In the readout circuit 113, the charge amount S is measured for each column by an integrating amplifier. The output of the integrating amplifier 105 is sampled and held at the timing indicated by "S" in FIG. 3(b), and is output from the readout circuit 113 via the A / D converter 110 as digital data indicating the charge amount S. The charge amount S is obtained by integrating the current flowing through the signal line during this step until the current settles down.

[0029] Third step S004: The difference between the charge amount N and the charge amount S is calculated based on the data obtained in the first and second steps. In this way, the charge amount associated with the transition of the gate potential of each switch element in the 0th row can be calculated. As will be described later, the charge amount that is the difference between the charge amount N and the charge amount S includes information about the threshold voltage.

[0030] The difference between the charge amount S and the charge amount N is the charge amount obtained by integrating the current that flows while the switch element transitions from a non-conducting state to a conducting state. Figure 3(b) shows that after the reset process, Vg on row 0 is changed to Voff and then to Von, and the difference between the charge amount N and the charge amount S on row 0 is obtained. In this way, by alternately performing the first and second processes for each row, the difference between the charge amounts obtained in the first and second processes can be obtained for all pixels.

[0031] The difference in the amount of charge contains information about the threshold voltage of the switching element. Details of obtaining information including the threshold voltage based on the difference between the amount of charge N and the amount of charge S will be described later.

[0032] Figure 4(a) shows an equivalent circuit diagram of one pixel on the sensor substrate, including the gate-source parasitic capacitance Cgs, which is one of the parasitic capacitances of the switch element. For ease of explanation, the source electrode and drain electrode of the switch element will be distinguished by calling the one connected to the signal line Vg the source electrode and the one connected to the individual electrode the drain electrode.

[0033] The parasitic capacitance Cgs varies depending on the gate voltage Vg. Figure 4(b) shows an example of a Cgs-Vg curve, which shows the dependence of the parasitic capacitance Cgs on the gate voltage of a normal pixel. Figure 4(c) shows an example of a curve showing the dependence of the parasitic capacitance Cgs on the gate voltage (Vg) of an abnormal pixel in which the threshold voltage of the switching element is shifted in the negative direction compared to normal pixels. The parasitic capacitance of a switching element generally varies depending on the gate voltage Vg. In an n-channel TFT, a positive gate bias results in an accumulation state in which the parasitic capacitance Cgs increases. Therefore, as shown in Figures 4(b) and 4(c), the value of Cgs increases at the threshold voltage V0. Now, when the drive line potential is switched from Voff to Von, switching each switching element from a non-conductive state to a conductive state, a charging current (denoted as displacement current I) for Cgs flows through the drive line and signal line. Consider the amount of charge q, which is the integral of the current I flowing through the signal line, in the readout circuit 113 connected to each signal line. In a normal pixel, the magnitude of q is represented by the area a1 of the hatched portion under the Cgs-Vg curve in Figure 4(b). The charge amount q corresponds to the charge amount obtained by integrating the current that flows while the drive line potential is transitioning from Voff to Von.

[0034] Using the charge amounts N and S determined in the first and second steps, the charge amount q = charge amount N - charge amount S, so the approximate threshold voltage V0 of each pixel can be estimated from the magnitudes of charge amounts N and S. Furthermore, if the shape of the Cgs-Vg curve, the maximum parasitic capacitance Cmax, and the minimum parasitic capacitance Cmin are known, the threshold voltage V0 of the switching element can be estimated more accurately from the charge amount q. In this invention, the acquisition of the charge amount q containing information about the threshold voltage V0 and the estimation and measurement of the threshold voltage V0 as described above are collectively referred to as measuring the threshold voltage V0.

[0035] If the threshold voltage V0 differs from pixel to pixel, the Cgs-Vg curve will also differ from pixel to pixel. Figure 4(c) shows an example of the Cgs-Vg curve for a pixel where V0 is shifted negatively compared to a normal pixel. The magnitude of the charge q' corresponding to the hatched area a2 is greater than the charge q (= a1) corresponding to the hatched area a1 shown in Figure 4(b). By utilizing this characteristic, the charge q measured in a normal pixel can be used as a reference value and compared with the charge q' measured in an abnormal pixel to determine whether the switch element is degraded or otherwise abnormal.

[0036] In addition to measuring the amount of charge as described above and determining the characteristics of the switching element based on the amount of charge, the threshold value of the switching element can be estimated as described above. To accurately estimate the threshold voltage V0 for each pixel, it is recommended to eliminate the influence of unnecessary charges in the photoelectric conversion element. To achieve this, (1) a reset process is performed before the first and second processes to remove dark charges in the photoelectric conversion element. Furthermore, (2) the amount of radiation irradiated to the radiation imaging device should be kept constant between the first and second processes, and it is even more recommended that radiation not be irradiated to the radiation imaging device between the first and second processes.

[0037] The threshold voltage V0 estimated as described above can be used to determine or predict the lifespan of the radiation imaging device. As an example of a method for determining the lifespan, pixels whose threshold voltage V0 of the switching element is outside a predetermined range (for example, +1 to -3 V) are defined as abnormal pixels. Next, the characteristics of the switching elements are determined based on the threshold voltages of the pixels in the effective area, and the control and calculation unit determines whether the total number of abnormal pixels (number of abnormalities) D exceeds a predetermined allowable value Dmax. When D>Dmax, it is determined that the radiation imaging device has reached the end of its lifespan, and the user may be notified by any means to request device replacement.

[0038] As an example of a lifespan prediction method, the future progression of deterioration may be predicted based on the transition of the threshold voltage V0 of each pixel and the number of abnormalities D, based on the time change of the threshold voltage V0 of each pixel, and the time when the number of abnormalities D will deviate from a predetermined allowable value Dmax. The measurement and determination of the threshold and the prediction of the lifespan may be performed by a computer based on information on the amount of charge output from the radiation imaging device.

[0039] (Modification of Example 1) Next, a modified example of the first embodiment will be described. Figures 5(a) and 5(b) are timing charts for calculating the average value of the threshold voltage V0 over the entire pixel region. The timing chart of Figure 5(a) will be described. In this case, the radiation imaging device is controlled by an operating method including the following steps.

[0040] Reset step S001: The same as in the first embodiment.

[0041] First step S002: The drive line potential Vg(0) of all rows is set to the non-conducting potential Voff, and the switch elements of all rows are set to the non-conducting state. As in the first embodiment, the integrating amplifier 105 is used for each column to integrate the current flowing through the signal line and output a voltage. The sample-and-hold circuit of the readout circuit 113 holds the voltage from the integrating amplifier 105 at the timing indicated by "N" in FIG. 5(a), and then outputs it from the readout circuit 113. Data indicating the charge amount N is output by the A / D converter 110, completing the measurement of the charge amount N.

[0042] Second step S003: The drive line potential of all rows is set to the conductive potential Von, and the switch elements of all rows are set to the conductive state. As in Example 1, the current flowing through the signal line is integrated using the integrating amplifier 105 for each column, and a voltage corresponding to the output voltage of the integrating amplifier 105 is sampled and held at the timing indicated by "S" in Figure 5(b) and output from the readout circuit 113. The output of the readout circuit 113 is A / D converted to digital data indicating the amount of charge S, and the measurement of the amount of charge S is completed.

[0043] Third process S004: In the same manner as in Example 1, find the difference between the charge amounts S and N, and obtain information including the threshold voltage V0 of the switching elements included in the pixels of all rows for each column. Further, by averaging the information obtained for each column over all columns, the average value over the entire pixel region of the information including the threshold voltage V0 can be measured. In a modified example, since the total charge amount of the pixels arranged in a column can be obtained, the tendency of the threshold voltage V0 of the switching elements can be understood. Even by such a method, deterioration of the entire radiation imaging apparatus can be determined.

[0044] Note that, as described above and as shown in FIG. 5(a), the first process and the second process may be continuously performed after a single reset process to obtain the charge amount N and the charge amount S, or as shown in FIG. 5(b), a reset process may be performed before the first process and the second process, respectively.

[0045] With reference to FIG. 6, supplement the threshold voltage measurement that can be performed in this modified example. For simplicity of explanation, assume that the number of pixels constituting the pixel region is 1 hundred, and all pixels are normal pixels (threshold voltage V0) or abnormal pixels (threshold voltage V0') similar to those in FIG. 4. FIG. 6(a) is a Cgs-Vg curve when all 100 pixels are normal pixels, and FIG. 6(b) is a Cgs-Vg curve when 90 out of 100 pixels are normal pixels and 10 are abnormal pixels.

[0046] In this modified example, the total charge amount for 100 pixels at Voff and Von can be obtained by performing the first process and the second process once each. In FIG. 6(a), the magnitude of the charge amount obtained in the first process and the second process, Q, is equal to 100 times the area a1. On the other hand, in FIG. 6(b), the total charge amount Q' for 100 pixels can be expressed as 90×a1 + 10×a2 using the areas a1 and a2 of Example 1. If V0' is a negative value compared to V0, then Q < Q', and it can be said that Q and Q' reflect the average value over the entire pixel region of the threshold voltage.

[0047] Note that Q and Q' are the summed charge amounts for multiple pixels, and it is not possible to uniquely determine the threshold voltage for each pixel from these. For example, it is impossible to separately determine the number of pixels whose thresholds have shifted from the amount of threshold shift. However, as described above, determining the average threshold voltage for the entire pixel region or for each region is often sufficient for determining or predicting the lifespan of the device. In this case, the lifespan of the device can be determined or predicted using a method and configuration simpler than those of Example 1.

[0048] Example 2 A radiation imaging apparatus according to this embodiment will be described with reference to Fig. 7. Description of the same configuration as in embodiment 1 will be omitted. The difference between embodiment 1 and this embodiment is that the bias power supply 103 functions as a charge measuring unit.

[0049] The bias power supply 103 outputs a bias potential Vs. In addition, since the bias power supply 103 functions as a charge measurement unit, it is configured to include an integrating amplifier that functions as a charge-to-voltage conversion circuit, as shown in Figure 7. Note that the circuit is not limited to an integrating amplifier as long as it can measure charge from the bias power supply.

[0050] Figure 8 shows an equivalent circuit diagram of one pixel on the sensor substrate in Figure 7, including the gate-drain capacitance (Cgd), which is one of the parasitic capacitances of the switching element. Similar to Figure 2(b), Cgd also depends on the gate voltage Vg and increases above the threshold voltage V0. When the drive line potential is switched from Voff to Von, a charging current (displacement current I) for Cgd flows from the drive line to the bias line. The parasitic capacitance Cgd varies depending on the gate voltage. A shift in the threshold voltage of the switching element also changes the Cgd-Vg curve. An integrating amplifier, which functions as a charge-voltage conversion circuit, is provided in the bias power supply 103. The amount of charge q, obtained by integrating the displacement current I flowing through the bias line by the integrating amplifier 105, corresponds to the area under the Cgd-Vg curve (not shown). Based on this, using the same procedure as in Example 1, the change in the threshold voltage of the switching element can be obtained from the difference in the amount of charge q. This allows the threshold voltage V0 for each pixel, as well as the average threshold voltage V0 for each region or the entire pixel region, to be estimated.

[0051] The bias line is a common line for all pixels and is connected to all pixels at once, which is more convenient than the first embodiment for finding the average value of information including the threshold voltage V0 over the entire pixel area.

[0052] In this embodiment, an example has been described in which the charge measurement unit is disposed within the bias power supply 103. However, the charge measurement unit may be provided as an independent circuit separate from the bias power supply 103, and the charge based on the displacement current I flowing through the bias line may be measured.

[0053] Furthermore, the charge measurement unit may measure the charge based on the control current flowing through the drive line, rather than based on the signal current of the signal line or the bias current of the bias line. In this case, an integrating circuit may be provided for each drive line to integrate the current flowing through the drive line wired from Voff to each gate and the current flowing through the drive line wired from Von to each gate. In this case, the charge at Voff and Von may be measured based on the output voltage of the integrating circuit provided for each drive line, and the difference may be used as the amount of charge when transitioning from Voff to Von. When measuring the current flowing through the drive line, the charge measured by the charge measurement unit is based on the sum of the charging current to Cgs and the charging current to Cgd. The information about the threshold voltage that can be obtained based on the charge is similar to the case of measuring the charge flowing through the signal line or the case of measuring the charge flowing through the bias line.

[0054] In the above explanations, the drive line potential is changed from Voff to Von, but this order may be reversed (from Von to Voff). The signs of the displacement current I and the charge quantity q are reversed, but the magnitudes remain the same, so the same discussion as above applies. It is also possible to reverse the order of the first and second steps in each of the above-mentioned embodiments.

[0055] (Other embodiments) The disclosure of the present specification includes the following radiation imaging device and method for operating the radiation imaging device. (Item 1) a plurality of pixels each including a conversion element that converts radiation or light into an electric charge and stores the electric charge, and a switch element that reads out an electric signal corresponding to the electric charge from the conversion element; a bias power supply that supplies a bias potential to the conversion element via a bias line; a drive circuit that supplies a control signal to a control electrode of the switch element via a drive line to control the switch element; a readout circuit that reads out an electrical signal from the switch element via a signal line; a charge measuring unit that measures an amount of charge based on a current flowing through any one of the signal line, the bias line, and the drive line; A method for operating a radiation imaging apparatus including a control and calculation unit, a measuring step of measuring the amount of charge by the charge measuring unit while the switching element is transitioning from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; a determining step of determining characteristics of the switching element based on the measured amount of charge by the control and calculation unit. (Item 2) In the measuring step, the amount of charge is measured while the switch elements provided in the plurality of pixels transition from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; 2. The method for operating a radiation imaging apparatus according to item 1, wherein the determining step determines characteristics of the switch elements included in the plurality of pixels based on the measured amounts of charge. (Item 3) 3. The method for operating a radiation imaging apparatus according to item 1 or 2, wherein the measuring step is carried out after the conversion elements are reset. (Item 4) 4. The method for operating a radiation imaging device according to any one of items 1 to 3, wherein the measurement step includes a first step of measuring a first amount of charge by the charge measuring unit when the switch element is controlled to a non-conductive state, a second step of measuring a second amount of charge by the charge measuring unit when the switch element is controlled to a conductive state, and a third step of calculating a difference between the first amount of charge and the second amount of charge. (Item 5) 5. The method for operating a radiation imaging apparatus according to any one of items 1 to 4, wherein the channel layer of the switching element is an oxide semiconductor. (Item 6) 6. The method for operating a radiation imaging apparatus according to any one of items 1 to 5, wherein the charge measuring unit has an integrating amplifier. (Item 7) 7. The method for operating a radiation imaging apparatus according to any one of items 1 to 6, wherein the characteristics of the switching element are determined by comparing the measured amount of charge with a predetermined reference value. (Item 8) 8. The method for operating a radiation imaging apparatus according to any one of items 1 to 7, wherein the characteristics of the switch elements include information about threshold voltages of the switch elements. (Item 9) Item 9. The method for operating a radiation imaging device according to item 8, further comprising a step in which the control calculation unit determines the state of the radiation imaging device by comparing the number of switch elements whose information on the threshold voltage is outside a predetermined range with an allowable value. (Item 10) a plurality of pixels each including a conversion element that converts radiation or light into an electric charge and stores the electric charge, and a switch element that reads out an electric signal corresponding to the electric charge from the conversion element; a bias power supply that supplies a bias potential to the conversion element via a bias line; a drive circuit that supplies a control signal to a control electrode of the switch element via a drive line to control the switch element; a readout circuit that reads out an electrical signal from the switch element via a signal line; a charge measuring unit that measures an amount of charge based on a current flowing through any one of the signal line, the bias line, and the drive line while the switch element transitions from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; a control calculation unit that determines characteristics of the switch element based on the amount of charge. (Item 11) the charge measurement unit measures the amount of charge while the switch elements included in the plurality of pixels transition from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; Item 11. The radiation imaging apparatus according to item 10, wherein the control and calculation unit determines characteristics of the switch elements provided in the plurality of pixels based on the measured amount of charge. (Item 12) 12. The radiation imaging apparatus according to item 10 or 11, wherein the charge measurement unit measures the amount of charge after the conversion element is reset. (Item 13) 13. The radiation imaging device according to any one of items 10 to 12, wherein the measurement of the charge amount includes determining a difference between a first charge amount measured when the switch element is controlled to a non-conductive state and a second charge amount measured when the switch element is controlled to a conductive state. (Item 14) 14. The radiation imaging device according to any one of items 10 to 13, wherein a channel layer of the switching element is an oxide semiconductor. (Item 15) 15. The radiation imaging apparatus according to any one of items 10 to 14, wherein the charge measuring unit has an integrating amplifier. (Item 16) 16. The radiation imaging apparatus according to any one of items 10 to 15, wherein the characteristics of the switching element are determined by comparing the measured amount of charge with a predetermined reference value. (Item 17) 17. The radiation imaging apparatus according to any one of items 10 to 16, wherein the characteristics of the switching elements include information about threshold voltages of the switching elements. (Item 18) Item 18. The radiation imaging device according to item 17, characterized in that the control calculation unit further determines the state of the radiation imaging device by comparing the number of switch elements whose information on the threshold voltage is outside a predetermined range with an allowable value.

[0056] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0057] Vg(0),...,Vg(Y-1): drive line potential, N, S: timing of sampling charge

Claims

1. a plurality of pixels each including a conversion element that converts radiation or light into an electric charge and stores the electric charge, and a switch element that reads out an electric signal corresponding to the electric charge from the conversion element; a bias power supply that supplies a bias potential to the conversion element via a bias line; a drive circuit that supplies a control signal to a control electrode of the switch element via a drive line to control the switch element; a readout circuit that reads out an electrical signal from the switch element via a signal line; a charge measuring unit that measures an amount of charge based on a current flowing through any one of the signal line, the bias line, and the drive line; A method for operating a radiation imaging apparatus including a control and calculation unit, a measuring step of measuring the amount of charge by the charge measuring unit while the switching element is transitioning from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; a determining step of determining characteristics of the switching element based on the measured amount of charge by the control and calculation unit.

2. In the measuring step, the amount of charge is measured while the switch elements provided in the plurality of pixels transition from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; 2. The method of claim 1, wherein the determining step determines characteristics of the switch elements included in the plurality of pixels based on the measured amounts of charge.

3. 2. The method for operating a radiation imaging apparatus according to claim 1, wherein the measuring step is carried out after the conversion elements are reset.

4. 2. The method for operating a radiation imaging device according to claim 1, wherein the measurement step includes a first step of measuring a first charge amount by the charge measuring unit when the switch element is controlled to a non-conductive state, a second step of measuring a second charge amount by the charge measuring unit when the switch element is controlled to a conductive state, and a third step of calculating a difference between the first charge amount and the second charge amount.

5. 2. The method for operating a radiation imaging apparatus according to claim 1, wherein the channel layer of the switching element is an oxide semiconductor.

6. 2. The method for operating a radiation imaging apparatus according to claim 1, wherein the charge measuring unit includes an integrating amplifier.

7. 2. The method of operating a radiation imaging apparatus according to claim 1, wherein the characteristics of the switching element are determined by comparing the measured amount of charge with a predetermined reference value.

8. 2. The method of claim 1, wherein the characteristics of the switching elements include information about threshold voltages of the switching elements.

9. 9. The method for operating a radiation imaging device according to claim 8, further comprising a step in which the control and calculation unit determines the state of the radiation imaging device by comparing the number of switch elements whose information about the threshold voltage is outside a predetermined range with an allowable value.

10. a plurality of pixels each including a conversion element that converts radiation or light into an electric charge and stores the electric charge, and a switch element that reads out an electric signal corresponding to the electric charge from the conversion element; a bias power supply that supplies a bias potential to the conversion element via a bias line; a drive circuit that supplies a control signal to a control electrode of the switch element via a drive line to control the switch element; a readout circuit that reads out an electrical signal from the switch element via a signal line; a charge measuring unit that measures an amount of charge based on a current flowing through any one of the signal line, the bias line, and the drive line while the switch element transitions from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; a control calculation unit that determines characteristics of the switch element based on the amount of charge.

11. the charge measurement unit measures the amount of charge while the switch elements included in the plurality of pixels transition from a non-conductive state to a conductive state or from a conductive state to a non-conductive state; 11. The radiation imaging apparatus according to claim 10, wherein the control and calculation unit determines characteristics of the switch elements included in the plurality of pixels based on the measured amounts of charge.

12. 11. The radiation imaging apparatus according to claim 10, wherein the charge measurement unit measures the amount of charge after the conversion element is reset.

13. 11. The radiation imaging device according to claim 10, wherein the measurement of the charge amount includes determining a difference between a first charge amount measured when the switch element is controlled to a non-conductive state and a second charge amount measured when the switch element is controlled to a conductive state.

14. 11. The radiation imaging apparatus according to claim 10, wherein the channel layer of the switching element is made of an oxide semiconductor.

15. 11. The radiation imaging apparatus according to claim 10, wherein the charge measuring unit includes an integrating amplifier.

16. 11. The radiation imaging apparatus according to claim 10, wherein the characteristics of the switching element are determined by comparing the measured amount of charge with a predetermined reference value.

17. 11. The radiation imaging apparatus according to claim 10, wherein the characteristics of the switching elements include information about threshold voltages of the switching elements.

18. 18. The radiation imaging apparatus according to claim 17, wherein the control and calculation unit further determines the state of the radiation imaging apparatus by comparing the number of the switch elements whose information about the threshold voltage is outside a predetermined range with an allowable value.

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