JP2022122046A - Radiation imaging device, radiation imaging system including the same, and structure inspection device - Google Patents

Abstract

To provide a radiation imaging device that is inexpensive so as to be applicable to general-purpose products, and enables high-speed driving, low power consumption, and acquisition of highly accurate image data.SOLUTION: A radiation imaging device according to the present invention uses, in a pixel circuit, a thin film transistor using an oxide semiconductor with a small off-current and a small hysteresis for a channel formation region as an amplifying element, and a thin film transistor using polycrystalline silicon for a channel formation region, which operates at high speed and can reduce power consumption as a switching element for outputting an electric signal from a pixel to a signal line.SELECTED DRAWING: Figure 1

Description

The present invention relates to a radiation imaging apparatus using X-rays and the like, and a radiation imaging system and a structure inspection apparatus equipped with the radiation imaging apparatus.

Devices that use radiation to image subjects and structures (hereinafter referred to as radiation imaging devices) are used in various fields such as the medical and industrial fields. An image diagnostic apparatus for imaging the inside of a human body using a medical imaging apparatus is widely used in the medical field.

In conventional radiation imaging apparatuses using X-rays, X-rays are emitted from an X-ray source to a specific part of a patient (bone, lung, etc.), and the X-rays that pass through the specific part are directly or indirectly detected by a sensor. It received light and acquired image data as digital data. Indirect means that radiation is received by a sensor after being converted into light of a wavelength that can be sensed by a photoelectric conversion element using a scintillator.

In such a radiation imaging apparatus, a general-purpose product has a pixel circuit composed of a thin film transistor using amorphous silicon or polycrystalline silicon. In addition, in high-performance products, the pixel circuit was constructed using single crystal silicon.

JP 2014-59293 A

However, in a configuration using amorphous silicon, it is difficult to shoot moving images at a high frame rate due to its low carrier mobility, and it is difficult to reduce the size of thin film transistors, resulting in large power consumption. there were. For this reason, in the case of battery drive, the camera must be recharged frequently, resulting in a situation in which shooting cannot be performed in an emergency. Further, when the amplifying element in the pixel circuit is made of amorphous silicon, hysteresis and off-current become problems, and it is difficult to acquire a highly accurate image.

In addition, in a configuration using polycrystalline silicon, the carrier mobility is 100 times faster than that of amorphous silicon, so it is possible to shoot moving images at a high frame rate, and the size of the thin film transistor can be reduced, so power consumption is low. It is possible to improve However, the problems of hysteresis and off-current in the amplifying element have not been solved, which has hindered acquisition of highly accurate image data. Diseases such as cancer are desirably discovered with very small lesions, but if the accuracy of the image data is low, such lesions appear unclear and pose the problem of being overlooked by doctors.

Also, in the case of a structure using single crystal silicon, there is no problem as described above, but it is very expensive and could only be used for high-performance high-end products.

In addition, in Japanese Patent Application Laid-Open No. 2004-59293, which is a prior document, a radiographic imaging device including a pixel in which a thin film transistor using polycrystalline silicon in a channel forming region and a thin film transistor using an oxide semiconductor in a channel forming region are mixed is disclosed. There are hints of equipment. However, the invention disclosed in this publication is characterized in that the channel formation region of the third transistor for storing charges generated by the photoelectric conversion element is formed of an oxide semiconductor. Polycrystalline silicon and oxide semiconductor are listed side by side as materials used for channel formation regions of the first transistor functioning as an amplifying element and the second transistor functioning as a switching element. However, as described in paragraphs 0071 to 0074, it suggests that it is preferable to use the same type of semiconductor material for the first transistor and the second transistor. There is no suggestion of

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional art. It is an object of the present invention to provide a radiation imaging apparatus that

The radiation imaging apparatus of the present invention comprises a conversion element that receives radiation or light converted from the radiation and generates charges, and a thin film transistor as an amplification element that is driven by a gate voltage based on the charges generated by the conversion element. , a thin film transistor as a first switch element for outputting an electric signal generated by the thin film transistor to a signal line, a channel forming region of the thin film transistor as the amplifying element being composed of an oxide semiconductor, the first The channel forming region of the thin film transistor as the switching element is made of polycrystalline silicon.

In the radiation imaging device of the present invention, in the pixel circuit, a thin film transistor using an oxide semiconductor having a small hysteresis and off current as a channel formation region is used as an amplification element, and a switching element for supplying an electric signal from the pixel to the signal line is used. A thin film transistor using polycrystalline silicon for a channel formation region, which operates at high speed and can reduce power consumption, is used.

In the present invention, by combining thin film transistors using different semiconductor materials, which has not been suggested in the past, it is possible to obtain a radiographic image at low cost, high-speed driving at a high frame rate, low power consumption, and high accuracy. We have realized the provision of a radiation imaging apparatus that

1 is a diagram showing the configuration of a radiation imaging apparatus according to the present invention; FIG. FIG. 2 is a diagram showing a circuit configuration of a pixel 5 shown in FIG. 1; FIG. 2 is a diagram showing the configuration of a conversion element and a thin film transistor of a pixel 5 shown in FIG. 1; 2A is a diagram showing a circuit configuration of a readout circuit 3 shown in FIG. 1, and FIG. 3B is a diagram showing a circuit configuration of a column circuit 202; FIG. FIG. 2 is a diagram showing an X-ray imaging system to which the radiation imaging apparatus shown in FIG. 1 is applied;

Embodiments to which the present invention can be suitably applied will be described in detail below with reference to the drawings. In the present invention, radiation refers to beams of particles (including photons) emitted by radiation decay such as α-rays, β-rays, and γ-rays. , particle beams, and cosmic rays are also included.

FIG. 1 shows a schematic configuration of a radiation imaging apparatus 1 of the present invention. As shown in FIG. 1, the radiation imaging apparatus has a plurality of pixels 5 formed on a substrate such as flat glass, each of which converts incident light or radiation into electrical signals. The pixel unit 4 constitutes a region (flat detector) in which a plurality of pixels 5 are arranged in a matrix. For example, a 17-inch radiation imaging device has about 2800 rows×about 2800 columns of pixels.

A gate driver 2 for driving the pixels 5, a readout circuit 3 for reading out electrical signals from the pixels 5, and a system control circuit 6 for controlling their operation timings are mounted on the substrate using solder or a conductive adhesive. are coupled to conductive paths such as metal traces on the substrate.

The gate driver 2 drives the pixel section 5 with a variable pixel addition number. The readout circuit 3 outputs the electric signal from the driven pixel unit 4 as image data digitized. The radiation imaging apparatus 1 further includes a signal processing unit (not shown) that processes image data from the readout circuit 3 and outputs the processed image data, a power supply unit (not shown) that supplies bias to each component, and the like.

The gate driver 2 receives a control signal from the system control circuit 6 and has a configuration capable of switching the scanning area and the pixel addition number. The power supply unit receives voltage from an external power supply (not shown) or a built-in battery, and includes a power supply circuit such as a regulator that supplies the voltage required by the gate driver 2, the readout circuit 3, the pixel unit 4, and the system control circuit 6. there is

Further, in this embodiment, the system control circuit 6 has a function capable of switching between a plurality of imaging operations. The imaging operation in the present invention has a plurality of parameters, and is determined by a combination of values of each parameter prepared in advance. The parameters include, for example, frame rate, amplification factor (gain), pixel addition number (binning). The number of pixel additions corresponds to the number of pixel rows driven simultaneously by the gate driver 2. For example, if the number of pixel rows driven simultaneously is one, the number of additions is 1, and the number of rows driven simultaneously is 1. If so, the number of additions is 2.

Next, the configuration and operation of the pixel 5 will be described with reference to FIG. The conversion element 21 is a photoelectric conversion element that converts radiation or light converted from radiation by a scintillator into charges. The switch element 21 (second switch element) has a function of switching the connection state between the conversion element 21 and the reset potential Vrst in order to initialize the conversion element 21 , and is controlled by the gate driver 2 via the drive wiring 26 . be done. Capacitor 23 has a function of holding the charge generated by conversion element 21 . The amplifying element 24 is driven by a gate voltage corresponding to the charges held in the capacitor 23, and generates an output current corresponding to the gate voltage at the drain electrode. The switch element 25 (first switch element) has a function of outputting the output current as an electric signal to the signal line 28 and is controlled by the gate driver 2 via the drive wiring 27 .

In this embodiment, as the conversion element 21, an indirect type having a scintillator that converts radiation into light in a wavelength band that can be detected by the conversion element 21 is used on the radiation incident side. Specifically, a PIN photodiode whose main material is amorphous silicon is used. In addition to the indirect type conversion element 21, a direct type conversion element that directly converts radiation into electric charges may be used. In that case, amorphous selenium, cadmium telluride, or the like is used as the main material.

As the switching elements 24 and 25 and the amplifying element 24, MOS transistors having a control terminal and two main terminals are preferably used, and thin film transistors (TFTs) are used in this embodiment. Details will be described later.

One electrode of the conversion element 21, the cathode, is electrically connected to one of the two main terminals of the switch element 22, the drain electrode, and the other electrode, the anode, is connected to a bias potential or a ground potential. A source electrode, which is the other main terminal of the switch element 22, is connected to the reset potential Vrst.

A drive wiring 26 for controlling the switch element 22 is electrically connected in common to control terminals of the switch element 22 of each of the plurality of pixels 5 existing in the same row direction, and the gate driver 2 outputs the conductive state of the switch element 22 . A drive signal is provided to control the In this manner, the gate driver 2 simultaneously controls the connection state and the non-connection state of the switching elements 22 of the plurality of pixels 5 present in the same row, so that the conversion elements 21 of the plurality of pixels 5 present in the same row are reset at the same time. Further, by simultaneously performing this reset operation for all rows, it is possible to initialize the conversion elements 22 of a plurality of pixels 5 existing in the pixel section 4 at the same time.

The drive wiring 27 for controlling the switch element 25 is electrically connected in common to the control terminals of the switch elements 25 of the plurality of pixels 5 existing in the same row direction, and the conduction state of the switch elements 25 is controlled by the gate driver 2 . A driving signal for control is given on a row-by-row basis. In this manner, the gate driver 2 controls the connection state and the non-connection state of the switch elements 25 in units of rows, so that electric signals from the pixels 5 can be output to the signal lines 28 in units of rows.

Next, operation of the pixel 5 will be described with reference to FIG. Prior to photographing the subject, drive signals for making the switch elements 22 conductive are simultaneously supplied from the gate driver 2 to the drive wirings 26 of all the rows, and the conversion elements 21 of the plurality of pixels 5 in the pixel section 4 are set at the reset potential Vrst. simultaneously connected to The conversion element 21 is in a state in which a reverse bias is applied when the cathode is set to the reset potential Vrst. This reset operation may be performed sequentially for each row instead of for all pixels at once. Further, during this reset operation, the capacitor 23 is also reset by the reset potential Vrst.

After that, the switch element 22 is driven to the non-conducting state again, but the conversion element 22 and the like maintain the reset state. Next, X-ray imaging is performed on the subject, and radiation, which is X-rays generated by imaging, or light converted from the radiation by a scintillator is incident on the conversion element 21 . The conversion element 21 generates an electric charge corresponding to the amount of incident radiation or light. The generated charge is accumulated in the capacitor 23 during a predetermined photographing time, and a voltage corresponding to the amount of accumulated charge is generated at one terminal thereof. The amplifying element 24 is driven using the generated voltage as a gate voltage, and generates an output current corresponding to the gate voltage at the drain electrode. The source electrode of the amplifying element 24 is connected to the bias potential VDD, forming a source follower circuit. After a predetermined imaging time, drive signals for making the switch elements 25 conductive are sequentially supplied from the gate driver 2 to the drive wiring 27 in units of rows, and the output currents of the pixels 5 existing in the same row are applied to the respective columns as electrical signals. They are sequentially output to the signal line 28 . This series of operations is the basic operation of each pixel 5 for acquiring an X-ray image of the subject. This is done by changing the frequency or the like for driving the element 25 .

Next, the readout circuit 3 will be described. The readout circuit 3 includes a column circuit 202 provided for each signal line 28 (each column of the pixel section 4), a multiplexer 203, a buffer amplifier 204, and an analog/digital converter (A/D converter) 205. . The configuration of each column circuit 202 will be described later in detail with reference to FIG. 4(b). The multiplexer 203 converts the parallel analog electrical signals output from each column circuit 202 into serial analog electrical signals. Buffer amplifier 204 transmits the serial analog electrical signal from multiplexer 203 to A/D converter 205 . The A/D converter 205 converts the analog electrical signal output from the buffer amplifier 204 into a digital electrical signal, and outputs the digital electrical signal to a subsequent signal processing circuit (not shown). The signal processing circuit performs predetermined or designated image processing on the input digital electrical signal as an image signal, and then outputs the image signal to the outside of the radiation imaging apparatus 1 .

The column circuit 202 will be described with reference to FIG. 4(b). The column circuit 202 comprises a voltage follower circuit, a low pass filter and a sample hold circuit. The voltage follower circuit includes a constant current source and an operational amplifier, and the operational amplifier has a positive input terminal connected to the signal line 28 and a negative input terminal and an output terminal connected to each other. One end of the signal line 28 is connected to one terminal of a constant current source, and the other terminal of this constant current source is connected to a bias potential VSS. The electric signal of the pixel 5 output to the signal line 28 is converted from a current signal to a voltage signal by this voltage follower circuit.

The sample-and-hold circuit has a first sample-and-hold section CDS1 and a second sample-and-hold section CDS2 that perform a holding operation to hold an input voltage signal. The first sample-and-hold section CDS1 is composed of a capacitive element C-CDS1 and a reset switch element SW-CDS1 connected to one electrode of the capacitive element C-CDS1. The second sample-and-hold section CDS2 is composed of a capacitive element C-CDS2 and a reset switch element SW-CDS2 connected to one electrode of the capacitive element C-CDS2. On/off of the reset switch elements SW-CDS1 and SW-CDS2 are controlled by control signals supplied from the system control circuit 6, respectively. When the reset switch element SW-CDS1 is switched from off to on, the first sample/hold section CDS1 switches from the hold mode to the sampling mode. During the sampling mode, the input signal to the first sample and hold unit charges the capacitive element C-CDS1. When the reset switch element SW-CDS1 is switched from on to off, the first sample and hold section switches from the sampling mode to the hold mode. During the hold mode, the signal held in the capacitive element C-CDS1 is held (fixed) and then supplied to the multiplexer 203 .

The basic operation of the second sample-and-hold section is the same, but the operating timing is different from that of the first sample-and-hold section, and as a result, the content of the electrical signal to be sampled/held is also different. Specifically, the first sample/hold section samples/holds an electrical signal as a noise signal during non-imaging, and the second sample/hold section samples/holds an electrical signal as an image signal during imaging. That is, the sample-and-hold circuit is for performing correlated double sampling (CDS). Both signals are differentially processed by a differential amplifier used as a buffer amplifier 204 to remove noise signal components from the image signal, and then sent to an A/D converter 205 .

A variable resistance element RLPF is connected between the voltage follower circuit and the sample-and-hold circuit. Variable resistance element RLPF changes its own resistance value according to a control signal supplied from system control circuit 6 . When the reset switch element SW-CDS1 is turned on, the variable resistance element RLPF and the capacitance element C-CDS1 are brought into a conductive state, and the variable resistance element RLPF and the capacitance element C-CDS1 form a low-pass filter. A low-pass filter is a filter circuit for filtering a signal output from an operational amplifier.

Next, details of the switch elements 22 and 25 and the amplifier element 24 of the pixel 5 provided in the pixel portion 4 will be described. The switch elements 22 and 25 and the amplifier element 24 are MOS transistors. The switch elements 22 and 25 are composed of thin film transistors using polysilicon for channel formation regions. The amplification element 24 is composed of a thin film transistor using an oxide semiconductor for a channel formation region.

Since polycrystalline silicon has a carrier mobility about 100 times higher than that of amorphous silicon, high-speed switching operation is possible. This means that information can be read out at high speed, and is suitable for, for example, a radiation imaging apparatus for motion picture imaging at a high frame rate. In addition, since it can be implemented as a thin film transistor with a small channel width due to high carrier mobility, it is possible to reduce the gate voltage and thus the power consumption.

Oxide semiconductors (amorphous indium gallium zinc oxide, etc.) have a carrier mobility that is about 20 times higher than that of amorphous silicon, and an off current that is much smaller than that of amorphous silicon or polycrystalline silicon.

This off current will be described in detail. An oxide semiconductor has a bandgap of 3.0 eV or more, which is much larger than the bandgap of silicon (1.1 eV). The off resistance of a thin film transistor is inversely proportional to the carrier concentration due to thermal excitation in the channel formation region. Since silicon has a bandgap of 1.1 electron volts, the concentration of thermally excited carriers at room temperature (200 K) is about 1×10 ¹¹ cm ⁻³ . On the other hand, the bandgap of an oxide semiconductor is as large as 3.0 electron volts or more. For example, when the bandgap is 3.2 electron volts, the concentration of thermally excited carriers is approximately 1×10 ⁻⁷ cm ⁻³ . Since resistivity is inversely proportional to carrier concentration for the same carrier mobility, the resistivity of a semiconductor with a bandgap of 3.2 eV is 18 orders of magnitude higher than that of silicon. Therefore, a thin film transistor in which an oxide semiconductor is used for a channel formation region can achieve extremely low off-state current.

In addition, when an oxide semiconductor is mounted as a thin film transistor, the channel length tends to be designed to be relatively short compared to amorphous silicon or polycrystalline silicon. Thereby, low hysteresis can be realized.

The amplifying element 24 is required to have a function of accurately amplifying the electric signal based on the charges generated by the converting element 21, and thus requires low hysteresis and high carrier mobility. On the other hand, a low off-state current is required in order to prevent unnecessary potential from being output to the bias potential VDD. Therefore, it is effective to use an oxide semiconductor material having properties such as low hysteresis, high carrier mobility, and low off current for the channel formation region. And this is an important performance for obtaining high-precision image data.

Conventionally, all the thin film transistors provided in the pixel section 4 were generally made of the same semiconductor material in order to reduce manufacturing costs. However, the thin film transistors in the pixel 5 have different functions, and different performances are required. Therefore, it is difficult to say that the conventional configuration is optimized in terms of performance.

In the present invention, the switch elements 22 and 24 are composed of thin film transistors using polycrystalline silicon for channel formation regions, and the amplifier element 24 is composed of thin film transistors using an oxide semiconductor for a channel formation region. This makes it possible to achieve high-speed readout, low power consumption during driving, and high-precision image data acquisition at the same time. As a result, it is possible to provide a radiation imaging apparatus that achieves high-precision, high-speed moving image capturing and low power consumption.

Next, the structure of one pixel of the thin film transistor and the conversion element in this embodiment will be described in more detail with reference to FIG.

A protective layer 31 made of SiON is provided on a flat glass substrate 30 . Layers 32-1, 32-2 and 32-3 made of polycrystalline silicon are formed on the protective layer 31 by a known manufacturing method and patterned. 32-1 constitutes a channel formation region of the switch element 22, 32-2 constitutes one electrode of the capacitor 23, and 32-3 constitutes a channel formation region of the switch element 25. FIG.

A gate insulating film 35 made of SiO is formed on the layer made of polycrystalline silicon. Metal layers 36-1, 36-2 and 36-3 made of Al or its alloy are formed on the gate insulating film 35 by patterning. 36-1 constitutes the gate electrode of the switch element 22, 36-2 constitutes the other electrode of the capacitor 23, and 36-3 constitutes the gate electrode of the switch element 25. FIG.

A protective layer (not shown) made of SiN is formed on the metal layers 36-1, 36-2, and 36-3, and an interlayer insulating film 36 made of SiO is formed thereon. Wiring layers 38, 39 and 41 made of Al or its alloy are formed on the interlayer insulating film 36 by patterning. This wiring layer may have a multi-layer structure in which layers made of Ti or TiN are provided above and below for adhesion to layers adjacent above and below and for prevention of migration. A wiring 38 is connected to the source electrode of the switch element 22 and supplies the reset potential Vrst. A wiring 39 electrically connects the drain electrode of the switch element 22, the cathode electrode of the conversion element 21, one terminal of the capacitor 23, and the gate electrode of the amplification element 24 to each other. A wiring 41 electrically connects the drain electrode of the switch element 25 and the signal line 28 . An interlayer insulating film 37 made of SiO is formed on the wiring layers 38 , 39 and 41 .

An oxide semiconductor layer 44 made of an oxide semiconductor (for example, indium gallium zinc oxide, etc.) is formed on the interlayer insulating film 37 by a known sputtering method, ALD method, or the like, and then patterned. Note that the oxide semiconductor layer 44 includes a channel forming region of the amplifying element 24 .

A wiring layer 40 made of Al or an alloy thereof, which also serves as the drain electrode of the amplifying element 24 , is formed by patterning in a state of hanging over one end of the oxide semiconductor layer 44 . The wiring layer 40 may have a multi-layer structure in which layers made of Ti and TiN are provided above and below in order to improve adhesion with layers adjacent above and below, prevent migration, and improve ohmic contact with the oxide semiconductor layer 44. good. This wiring layer 40 is connected to the source electrode of the switch element 25 through a contact hole.

An interlayer insulating film 43 made of SiO is formed on the wiring layer 40 and the oxide semiconductor layer 44 . A wiring layer 45 made of Al or an alloy thereof is formed on the interlayer insulating film 43 by patterning. This wiring layer 45 also serves as the source electrode of the amplifying element 24 and supplies the bias potential VDD to the amplifying element 24 .

A planarization layer 46 made of TEOS or the like is formed on the wiring layer 45 . A conversion element 21 is formed on the planarization layer 46 . The conversion element 21 includes, from the flattening layer 46 side, a cathode 48 made of a metal such as Al, a P-type semiconductor layer 50 made of Si or the like, an I-type semiconductor layer 51 and an N-type semiconductor layer 52, and an anode 53 made of a metal such as Al. are stacked in that order. Cathode 48 is electrically connected to a portion of wiring layer 39 through contact hole 47 formed in planarization layer 46 . A bank layer 49 made of SiO is formed on the end of the cathode 48 and the contact hole 47 . The bank layer 49 is formed for the purpose of preventing short-circuiting with the anode 53 at the end of the cathode 48 of the conversion element 21 , flattening the contact hole 47 , and defining the layout of the conversion element 21 .

A thin film transistor using an oxide semiconductor for a channel formation region is generally an n-channel device (that is, an NMOS transistor). A thin film transistor made of polycrystalline silicon can be designed as either a p-channel device or an n-channel device, but in this embodiment a PMOS is used.

The structure described above can be easily manufactured using well-known semiconductor processes. The polycrystalline silicon forming one terminal of the capacitor 23 may be doped with an impurity to increase conductivity. Moreover, the contact portions between the source/drain electrodes of the switch elements 22, 25 and the amplifier element 24 and the polycrystalline silicon may be silicided. Also, a metal such as Mo or an alloy other than Al may be used for the wiring layer. A shield layer made of metal may be provided between the interlayer insulating films for the purpose of shielding the channel forming region made of polycrystalline silicon or oxide semiconductor from light. Also, the oxide semiconductor layer 44 may be amorphous, crystalline, or a mixture thereof.

Next, a radiation imaging system to which the radiation imaging apparatus of the present invention is applied will be described with reference to FIG.

In FIG. 5, 60 is an X-ray source that generates X-rays. Reference numeral 61 denotes a subject to be imaged or an affected part of the subject. 63 is the radiation imaging apparatus of the present invention. Reference numeral 62 denotes a support that encloses and supports the radiation imaging apparatus, and is arranged to face the X-ray source 60 with the subject 61 interposed therebetween. Reference numeral 64 denotes a computer that controls the radiation imaging apparatus 63, and transmits to the system control circuit 6 of the radiation imaging apparatus 63 instructions for switching among a plurality of types of imaging operations, timing instructions for starting, interrupting, and stopping imaging operations. do. It also acquires image data taken from the radiation imaging device 63 , performs further image processing, and displays it on the display 65 .

Next, the imaging method will be described. A subject 61 places an affected area to be imaged in front of a radiation imaging device 63 supported on a support 62 in accordance with instructions from a doctor or technician. A doctor or a technician operates the computer 64 to activate the radiation imaging apparatus 63 and set it to a ready state.

The radiation imaging apparatus 63 placed in the ready state supplies a drive signal from the gate driver 2 to the switch element 22 through the drive wiring 26 to bring it into a conducting state. When the switch element 22 is turned on, the cathode of the conversion element 21, one electrode of the capacitor 23, and the gate electrode, which is the control electrode of the amplification element 24, are reset to the reset potential Vrst. This reset operation is performed for all pixels of the pixel section 4 . In this state, the gate driver 2 supplies a drive signal to the switch element 25 via the drive wiring 27, and outputs the current generated at the drain electrode of the amplifier element 25 with the reset potential Vrst as the gate potential to the signal line 28 as an electrical signal. . The current output to the signal line 28 is converted into a voltage by the operational amplifier of the column circuit 202 in the readout circuit 3, and then held as a noise signal (dark current signal) during non-shooting by the first sample-and-hold unit. . The above is the operation in the ready state, and when the ready state is completed, the radiation imaging apparatus 63 notifies the computer that it is ready for imaging.

The doctor or technician informed that the imaging is possible operates the X-ray source 60 to emit X-rays toward the affected area of the subject 61 . X-rays emitted from the X-ray source 60 pass through the affected area of the subject 61 and are received by the pixel section 4 of the radiation imaging device 63 directed to the support 62 . The received X-rays are converted into light having a wavelength that can be detected by the conversion element 21 by a scintillator arranged on the light receiving surface side of the radiation imaging device 63 . The converted light is received and photoelectrically converted by each of the conversion elements 21 to generate an amount of charge corresponding to the amount of received light. The generated charge is accumulated in the capacitor 23 of each pixel 5 for a predetermined imaging time, and the voltage generated at one terminal of the capacitor 23 by the accumulated charge is used as the gate voltage to drive the amplifying element 24 . A current is generated at the drain electrode of the amplifying element 24 .

Although not shown, the radiation imaging device 63 has a known X-ray incident automatic detection function for detecting incident X-rays. The X-ray incidence automatic detection function transmits a detection signal to the system control circuit 6 when X-ray incidence is detected. After receiving the detection signal, the system control circuit 6 starts driving the gate driver 2 and the readout circuit 3 to read out the generated current as an electric signal after a predetermined imaging time has elapsed. At this time, the gate driver 2 drives the pixels 5 of the pixel section 4 on a row-by-row basis. Here, the number of binnings is set to 1, and reading out in units of one row will be described as an example.

A drive signal supplied from the gate driver 2 through the drive wiring 26 is simultaneously supplied to the gate electrodes 36-3 of the switch elements 25 in the plurality of pixels 5 arranged in the first row, and the switch elements 25 are turned on. state. Then, the current flowing through the drain electrode of the switch element 25 is output as an electric signal to each signal line 28 provided in each pixel column of the pixel section 4 .

The current output to the signal line 28 is converted into voltage by the operational amplifier of each column circuit 202 in the readout circuit 3, and then sampled and held by the second sample and hold section as an image signal at the time of photographing. Next, the multiplexer 203 sequentially reads the voltage signals held by the capacitive element C-CDS1 of the first sample-and-hold section and the capacitive element C-CDS2 of the second sample-and-hold section of each column circuit 202 for each signal line. The buffer amplifier 204 takes the differential between the voltage signal held by the capacitive element C-CDS1 and the voltage signal held by the capacitive element C-CDS2 transmitted from the multiplexer 203 and transmits the difference to the A/D converter 205 . The A/D converter 205 converts the differential signal output from the buffer amplifier 204 into a digital electrical signal, and outputs the digital electrical signal to a subsequent signal processing circuit (not shown).

The above processing is sequentially repeated for each column circuit in units of rows, and electric signals as image signals are read out from all the pixels 5 of the pixel section 4 . The image signal read out by the readout circuit 3 is subjected to predetermined image processing by a signal processing circuit (not shown), transmitted from the radiation imaging apparatus 1 to the computer 64, and displayed on the display 65 as image data. be. A doctor diagnoses the affected part of the subject 61 based on the image displayed on the display.

In the above embodiments, the radiation imaging apparatus for medical use has been described, but the radiation imaging apparatus of the present invention is not limited to this application, and can be applied to a structure inspection apparatus for inspecting the internal structure of a building or the like. It is possible.

Reference Signs List 1, 63 radiation imaging apparatus 2 gate driver 3 readout circuit 4 pixel section 5 pixel 21 conversion element 22 second switch element 23 capacitor 24 amplification element 25 first switch element 26, 27 drive wiring 28 signal line 30 substrate 31 protective layer 32 polycrystalline silicon 35 gate insulating film 36 metal layer 37, 43 interlayer insulating film 38, 39, 40, 41, 45 wiring layer 44 oxide semiconductor 46 planarizing layer 47 contact hole 48 cathode electrode 49 bank layer 50 p-type semiconductor layer 51 I-type semiconductor layer 52 N-type semiconductor layer 53 anode electrode 60 X-ray source 61 subject 62 support 64 computer 65 display 202 column circuit 203 multiplexer 204 buffer amplifier 205 ADC

Claims (12)

a conversion element that receives radiation or light converted from the radiation and generates an electric charge;
a thin film transistor as an amplifying element driven by a gate voltage based on the charge generated by the conversion element;
a thin film transistor as a first switching element that outputs an electrical signal generated by the thin film transistor to a signal line;
A radiation imaging device, wherein a channel forming region of a thin film transistor as said amplifying element is made of an oxide semiconductor, and a channel forming region of said thin film transistor as said first switching element is made of polycrystalline silicon. 2. A radiation imaging apparatus according to claim 1, further comprising a thin film transistor as a second switch element connecting said conversion element and a reset potential, wherein a channel forming region of said thin film transistor is made of polycrystalline silicon. 3. The radiation imaging device according to claim 2, wherein the oxide semiconductor is indium gallium zinc oxide. 4. The radiation imaging device according to claim 3, wherein said oxide semiconductor is amorphous. 5. A radiation imaging apparatus according to claim 4, further comprising a scintillator for converting said radiation into light having a wavelength to which said conversion element can be sensitive. 6. A radiation imaging apparatus according to claim 5, wherein said conversion element is a PIN photodiode. 7. The radiation imaging apparatus according to claim 6, further comprising a capacitor connected to a gate electrode of a thin film transistor as said amplifying element for storing charges generated by said conversion element. 8. The radiation imaging apparatus according to claim 7, further comprising a plurality of pixels, each pixel having said conversion element, said amplification element, said first switch element, and said second switch element. 9. The radiation imaging apparatus according to claim 8, further comprising a gate driver that drives the plurality of first switch elements and second switch elements. The electrical signal output to the signal line during non-shooting and the electrical signal output to the signal line during shooting are sampled and held, and the sampled and held electrical signals are differentiated, converted to a digital electrical signal, and output. 10. The radiographic imaging apparatus according to claim 9, further comprising a readout circuit for reading. a radiation imaging apparatus according to claim 10;
a computer that controls the radiation imaging device;
a display for displaying image data instructed by the computer;
and an X-ray source that emits X-rays to the radiation imaging device. A structure inspection apparatus comprising the radiation imaging apparatus according to claim 10 .

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