JP2019153692A - Radiation imaging device and radiation imaging system - Google Patents

Abstract

To provide a technique capable of taking an energy subtraction image with a simple and convenient element structure.SOLUTION: A radiation imaging device comprises: a light transmitting substrate with a plurality of photoelectric conversion elements which are arranged like a two-dimensional array on a first face side; a first scintillator arranged so as to hold the substrate and the plurality of photoelectric conversion elements therebetween; and a second scintillator disposed on a second face side of the substrate opposite to the first face side thereof. The plurality of photoelectric conversion elements include a first photoelectric conversion element and a second photoelectric conversion element. The second photoelectric conversion element includes a metal conductive layer serving as a first electrode, an impurity semiconductor layer, a semiconductor layer, and a second electrode from the side of the substrate in turn. The first photoelectric conversion element includes no metal conductive layer, an impurity semiconductor layer serving as a first electrode, a semiconductor layer, and a second electrode from the side of the substrate in turn.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a radiation imaging apparatus and a radiation imaging system.

  As an imaging apparatus used for medical image diagnosis and nondestructive inspection, there is a radiation imaging apparatus including an imaging panel in which pixels in which a combination of a conversion element that converts radiation into electric charge and a switching element such as a thin film transistor (TFT) are arranged in an array Widely used. Using such a radiation imaging apparatus, a method of acquiring a plurality of radiation images using radiation having different energy components, and acquiring an energy subtraction image in which a specific subject portion is separated or emphasized from a difference of the acquired radiation images It has been known. In Patent Document 1, scintillators are arranged on both surfaces of a light-transmitting substrate, and a photodiode for detecting light emitted from one side of the scintillator and a photodiode for detecting light emitted from the other side of the scintillator are arranged. Has been shown to do. By detecting light emitted from different scintillators, signals of two different energy components are acquired by one irradiation of radiation, and an energy subtraction image can be generated.

JP 2010-56396 A

  In Patent Document 1, it is necessary that the light of one of the photodiodes be light-transmitting and the light of the other photodiode be light-shielding with respect to light from one scintillator. Therefore, in order to generate one pixel data of a radiographic image, two photodiodes having different conductive materials used for the electrodes are used, so that the element structure becomes complicated and the manufacturing cost may increase.

  An object of the present invention is to provide a technique capable of acquiring an energy subtraction image with a simple element structure.

  In view of the above problems, a radiation imaging apparatus according to an embodiment of the present invention includes a substrate that transmits light in which a plurality of photoelectric conversion elements are arranged in a two-dimensional array on the first surface side, the substrate, and the substrate. Radiation comprising: a first scintillator disposed so as to sandwich a plurality of photoelectric conversion elements; and a second scintillator disposed on the second surface side opposite to the first surface of the substrate. In the imaging apparatus, the plurality of photoelectric conversion elements include a first photoelectric conversion element and a second photoelectric conversion element, and the second photoelectric conversion element is first in order from the substrate side. A metal conductive layer functioning as an electrode; an impurity semiconductor layer; a semiconductor layer; and a second electrode. The first photoelectric conversion element includes a metal conductive layer in order from the substrate side. In addition, the impurity semiconductor layer functioning as the first electrode, the semiconductor layer, and the second Characterized in that it comprises a pole, a.

  By the above means, there is provided a technique capable of efficiently selecting light emitted from phosphors arranged on the front and back with a simple element structure and efficiently receiving light.

The figure which shows the structural example of the radiation imaging system using the radiation imaging device which concerns on embodiment of this invention. The figure which shows the structural example of the imaging panel of the radiation imaging device of FIG. The figure which shows the structural example of the cross section of the pixel of the radiation imaging device of FIG. The figure which shows the example of arrangement | positioning of the pixel of the radiation imaging device of FIG. 2 is a timing chart showing the operation of the radiation imaging apparatus of FIG. 2 is a timing chart showing the operation of the radiation imaging apparatus of FIG. The figure which shows the operation | movement flow of the radiation imaging device of FIG. The figure which shows the example of the pixel interpolation of the radiation imaging device of FIG.

  Hereinafter, specific embodiments of a radiation imaging apparatus according to the present invention will be described with reference to the accompanying drawings. Note that, in the following description and drawings, common reference numerals are given to common configurations over a plurality of drawings. Therefore, a common configuration is described with reference to a plurality of drawings, and a description of a configuration with a common reference numeral is omitted as appropriate. The radiation in the present invention includes a beam having energy of the same degree or more, such as X-rays, β-rays, γ-rays, etc., which are beams formed by particles (including photons) emitted by radiation decay, such as X It can also include rays, particle rays, and cosmic rays.

  With reference to FIGS. 1-8, the structure and operation | movement of the radiation imaging device by embodiment of this invention are demonstrated. FIG. 1 is a diagram illustrating a configuration example of a radiation imaging system 200 using a radiation imaging apparatus 210 according to an embodiment of the present invention. The radiation imaging system 200 is configured to electrically capture an optical image converted from radiation and obtain an electrical signal (radiation image data) for generating a radiation image. The radiation imaging system 200 includes, for example, a radiation imaging apparatus 210, a radiation source 230, an exposure control unit 220, and a computer 240.

  The radiation source 230 starts radiation emission in accordance with an exposure command (radiation command) from the exposure control unit 220. The radiation emitted from the radiation source 230 is irradiated to the radiation imaging apparatus 210 through an unillustrated object. The radiation source 230 also stops radiation emission according to a stop command from the exposure control unit 220.

  The radiation imaging apparatus 210 includes an imaging panel 212 and a control unit 214 that controls the imaging panel 212. The control unit 214 generates a stop signal for stopping radiation emission from the radiation source 230 based on a signal obtained from the imaging panel 212. The stop signal is supplied to the exposure control unit 220, and the exposure control unit 220 sends a stop command to the radiation source 230 in response to the stop signal. The control unit 214 is, for example, PLD (abbreviation of Programmable Logic Device) such as FPGA (abbreviation of Field Programmable Gate Array), or ASIC (abbreviation of Application Specific Integrated Computer, or an abbreviation of a computer program integrated with a computer). Or a combination of all or part of them.

  The computer 240 controls the radiation imaging apparatus 210 and the exposure control unit 220. The computer 240 also includes a signal processing unit 241 that receives the radiation image data output from the radiation imaging apparatus 210 and processes the radiation image data. The signal processing unit 241 can generate a radiation image from the radiation image data.

  The exposure control unit 220 has an exposure switch (not shown) as an example. When the exposure switch is turned on by the user, the exposure control unit 220 sends an exposure command to the radiation source 230 and starts indicating the start of radiation emission. A notification is sent to the computer 240. Upon receiving the start notification, the computer 240 notifies the control unit 214 of the radiation imaging apparatus 210 of the start of radiation emission in response to the start notification.

  FIG. 2 shows a configuration example of the imaging panel 212. The imaging panel 212 includes a pixel array 112. The pixel array 112 includes a plurality of pixels PIX each including photoelectric conversion elements S arranged in a two-dimensional array for detecting radiation. Further, the pixel array 112 includes a plurality of column signal lines Sig1 to Sig4 along the column direction (vertical direction in FIG. 2) for outputting the signal generated by the photoelectric conversion element S. Further, the imaging panel 212 includes a drive circuit (row selection circuit) 114 that drives the pixel array 112 and a readout circuit 113 for detecting a signal that appears on the column signal line Sig of the pixel array 112. In the configuration shown in FIG. 2, for simplification of description, the pixel array 112 is configured by 4 rows × 4 columns of pixels PIX, but in reality, more pixels PIX can be arranged. In one example, the imaging panel 212 may have dimensions of 17 inches and may have approximately 3000 rows by approximately 3000 columns of pixels PIX.

  Each pixel PIX includes a photoelectric conversion element S for detecting radiation, and a photoelectric conversion element S and a column signal line Sig for each photoelectric conversion element (a signal line Sig corresponding to the photoelectric conversion element C among the plurality of signal lines Sig). And a switch element T for connecting the two. Each photoelectric conversion element S outputs a signal corresponding to the amount of incident radiation to the column signal line Sig. As the photoelectric conversion element S, for example, a PIN type photodiode that is disposed on an insulating substrate such as a glass substrate and mainly uses amorphous silicon can be used. In the present embodiment, the conversion element S can be configured as an indirect element that detects light after the radiation is converted into light by a scintillator. In the indirect element, the scintillator can be shared by a plurality of pixels PIX (a plurality of photoelectric conversion elements S).

  The switch element T can be configured by a transistor such as a thin film transistor (TFT) having a control terminal (gate) and two main terminals (source, drain), for example. The photoelectric conversion element S has two main electrodes, one main electrode of the photoelectric conversion element S is connected to one of the two main terminals of the switch element T, and the other main electrode of the photoelectric conversion element S Are connected to a bias power supply 103 via a common bias line Bs. The bias power supply 103 supplies a bias voltage Vs. The control terminal of the switch element T of each pixel PIX arranged in the first row is connected to the gate line Vg1 arranged along the row direction (lateral direction in FIG. 2). Similarly, the control terminals of the switches SW of the respective pixels PIX arranged in the second to fourth rows are connected to the gate lines Vg2 to Vg4, respectively. A gate signal is supplied to the gate lines Vg1 to Vg4 by the drive circuit 114.

  In each pixel PIX arranged in the first column, the main terminal of the switch element T that is not connected to the photoelectric conversion element S is connected to the column signal line Sig1 in the first column. Similarly, in each pixel PIX arranged in the second to fourth columns, the main terminal on the side not connected to the photoelectric conversion element S of the switch element T is connected to the column signal lines Sig2 to Sig4 in the second to fourth columns, respectively. Is done.

  The read circuit 113 has a plurality of column amplifiers CA so that one column amplifier CA corresponds to one column signal line Sig. Each column amplifier CA may include an integrating amplifier 105, a variable amplifier 104, a sample hold circuit 107, and a buffer circuit 106. The integrating amplifier 105 amplifies the signal appearing on the column signal line Sig. The integrating amplifier 105 can include an operational amplifier and an integrating capacitor and a reset switch connected in parallel between the inverting input terminal and the output terminal of the operational amplifier. A reference potential Vref is supplied to the non-inverting input terminal of the operational amplifier. The integration capacitor is reset by turning on the reset switch, and the potential of the column signal line Sig is reset to the reference potential Vref. The reset switch can be controlled by a reset pulse RC supplied from the control unit 214.

  The variable amplifier 104 amplifies the signal output from the integrating amplifier 105 with a set amplification factor. The sample hold circuit 107 samples and holds the signal output from the variable amplifier 104. The sample hold circuit 107 can be configured by a sampling switch and a sampling capacitor. The buffer circuit 106 buffers the signal output from the sample hold circuit 107 (impedance conversion) and outputs the result. The sampling switch can be controlled by a sampling pulse supplied from the control unit 214.

  Read circuit 113 also includes a multiplexer 108 that selects and outputs signals from a plurality of column amplifiers CA provided in correspondence with each column signal line Sig in a predetermined order. The multiplexer 108 includes, for example, a shift register. The shift register performs a shift operation in accordance with the clock signal CLK supplied from the control unit 214, and one signal from the plurality of column amplification units CA is selected by the shift register. Read circuit 113 further includes a buffer 109 for buffering (impedance conversion) the signal output from multiplexer 108 and an AD converter 110 for converting an analog signal output from buffer 109 into a digital signal. sell. The output of the AD converter 110, that is, radiation image data is transferred to the computer 240.

  In the present embodiment, as will be described later, on both the incident surface (first surface) side for allowing the radiation of the substrate to enter and the back surface (second surface) opposite to the incident surface. A scintillator for converting radiation into visible light is arranged so as to cover each surface. The photoelectric conversion element S included in each pixel PIX includes two types of photoelectric conversion elements S. In the configuration shown in FIG. 2, the photoelectric conversion elements S12, S14, S21, S23, S32, S34, S41, and S43 are arranged to receive light from two scintillators. Below, when specifying these photoelectric conversion elements which receive the light from two scintillators among the photoelectric conversion elements S, it calls the 1st photoelectric conversion element 901. In the photoelectric conversion elements S11, S13, S22, S24, S31, S33, S42, and S44, a light shielding layer 903 is disposed between the scintillator on the back surface and the photoelectric conversion element S. Accordingly, the photoelectric conversion elements S11, S13, S22, S24, S31, S33, S42, and S44 are arranged so that light from the scintillator on the back surface is blocked and light from the scintillator on the incident surface is received. Hereinafter, these photoelectric conversion elements S are referred to as second photoelectric conversion elements 902 when the photoelectric conversion elements S among the photoelectric conversion elements S from which light from the scintillator on the back surface is blocked are specified. The light-blocking layer 903 is a layer that blocks light emitted from the scintillator, and may block light between the scintillator that covers the back side of the substrate and the second photoelectric conversion element 902. At this time, in the second photoelectric conversion element 902, the light from the scintillator on the back surface may not be completely blocked. A light shielding layer 903 is disposed between the scintillator that covers the back side of the substrate and the second photoelectric conversion element 902 so that the amount of light that can be received from the back scintillator is smaller than that of the first photoelectric conversion element 901. It only has to be done.

  Here, a light shielding layer 903 is disposed between the scintillator disposed on the back surface side of the substrate and the second photoelectric conversion element 902. Therefore, of the radiation incident from the incident surface side of the substrate, the low energy component is absorbed by the scintillator that covers the incident surface side of the substrate, is converted into visible light, and enters each pixel PIX. Moreover, the high energy component which was not absorbed by the scintillator arranged on the incident surface side of the substrate in the radiation is absorbed by the scintillator covering the back surface side of the substrate and converted into visible light. In the second photoelectric conversion element 902, since the back surface side of the substrate is shielded from light, light emitted from the back surface side of the substrate does not enter. Therefore, light converted from a component with high energy of radiation does not enter the second photoelectric conversion element 902. On the other hand, since the first photoelectric conversion element 901 is not provided with the light shielding layer 903, light converted from a component having high radiation energy is incident thereon.

  As described above, in the first photoelectric conversion element 901, a signal caused by a high energy component and a low energy component of radiation, and in the second photoelectric conversion element 902, a signal caused by a low energy component of radiation. Can be acquired respectively. That is, information on different radiation energies can be held in the pixels PIX adjacent to each other. By holding information acquired from radiation of different energy components in adjacent pixels PIX in this way, energy subtraction can be performed using a method described later.

  FIG. 3 schematically illustrates an example of a cross-sectional structure of the pixel PIXA, the pixel PIXC, and the pixel PIXB having the first photoelectric conversion element 901 and the pixel PIXB having the second photoelectric conversion element 902. Here, the radiation is described as being incident from the upper side of the drawing, but the radiation may be incident from the lower side of the drawing. 3A, the first photoelectric conversion element 901 and the second photoelectric conversion element 902 are disposed between the substrate 310 and the scintillator 904 disposed on the incident surface (first surface) side of the substrate 310. Is done. Further, FIG. 3A shows a case where the light shielding layer 903 is arranged between the second photoelectric conversion element 902 and the scintillator 905 in the pixel PIXB. 3B and 3C illustrate that the first photoelectric conversion element 901 and the second photoelectric conversion element 902 are arranged between the substrate 310 and the scintillator 904 that covers the incident surface side of the substrate 310. It is the same as FIG. 3A. On the other hand, in the configuration of FIG. 3C, in the pixel PIXD, the light shielding layer 903 is disposed between the first photoelectric conversion element 901 and the scintillator 904 disposed on the incident surface (first surface) side of the substrate 310. The case where it is arranged is shown. 3B and FIG. 3C show the area of the first photoelectric conversion element 901 of the pixel PIXC and the pixel PIXD as compared with the second photoelectric conversion element 902 of the pixel PIXB in a plan view to the substrate 310. It is small.

  The photoelectric conversion element S of each pixel PIX is disposed on an insulating substrate 310 such as a glass substrate that transmits light emitted from the scintillators 904 and 905. Each pixel PIX includes a conductive layer 311, an insulating layer 312, a semiconductor layer 313, an impurity semiconductor layer 314, and a conductive layer 315 in this order on a substrate 310. The conductive layer 311 constitutes a gate electrode of a transistor (for example, TFT) constituting the switch element T. The insulating layer 312 is disposed so as to cover the conductive layer 311, and the semiconductor layer 313 is disposed on a portion of the conductive layer 311 that constitutes the gate electrode with the insulating layer 312 interposed therebetween. The impurity semiconductor layer 314 is disposed on the semiconductor layer 313 so as to constitute two main terminals (source and drain) of the transistor constituting the switch element T. The conductive layer 315 constitutes a wiring pattern that is electrically connected to each of two main terminals (source and drain) of the transistor that constitutes the switch element T. A part of the conductive layer 315 constitutes a column signal line Sig, and the other part constitutes a wiring pattern for connecting the photoelectric conversion element S and the switch element T.

  Each pixel PIX further includes an interlayer insulating film 316 that covers the insulating layer 312 and the conductive layer 315. The interlayer insulating film 316 is provided with a contact plug 317 for connecting to a portion of the conductive layer 315 constituting the switch element T. Each pixel PIX includes a photoelectric conversion element S disposed on the interlayer insulating film 316. In the example illustrated in FIG. 3, the photoelectric conversion element S is configured as an indirect photoelectric conversion element that converts light converted from radiation by the scintillators 904 and 905 into an electrical signal. The photoelectric conversion element S includes a conductive layer 318, an insulating layer 319, a semiconductor layer 320, an impurity semiconductor layer 321, a conductive layer 322, and an electrode layer 325 stacked on the interlayer insulating film 316 in order from the substrate 310 side. A protective layer 323 and an adhesive layer 324 are disposed on the photoelectric conversion element S. The scintillator 904 is disposed on the adhesive layer 324 so as to cover the incident surface side of the substrate 310. The scintillator 905 is arranged so as to cover the back surface side opposite to the incident surface of the substrate 310.

  Here, the second photoelectric conversion element 902 includes a metal conductive layer 318 that functions as a lower electrode (first electrode), and the first photoelectric conversion element 901 functions as a lower electrode (first electrode). There is no conductive layer 318 of metal to be used. In addition, the conductive layer 322 and the electrode layer 325 constitute an upper electrode (second electrode) of each photoelectric conversion element S. The impurity semiconductor layer 319, the semiconductor layer 320, the impurity semiconductor layer 321, and the conductive layer 322 constitute a PIN photodiode as the photoelectric conversion element S. For example, the impurity semiconductor layer 319 is formed of an n-type impurity semiconductor layer, and the impurity semiconductor layer 321 is formed of a p-type impurity semiconductor layer. Here, the impurity semiconductor layer 319 may be a p-type impurity semiconductor layer, and the impurity semiconductor layer 321 may be an n-type impurity semiconductor layer. With this structure, the first photoelectric conversion element 901 does not have the metal conductive layer 318 and the impurity semiconductor layer 319 functions as a lower electrode, so that light from the scintillator 905 can enter the semiconductor layer 320. . Since the impurity semiconductor layer 319 is a material having higher resistance than a metal, the area of the first photoelectric conversion element 901 is as viewed in a plan view with respect to the substrate 310 as illustrated in FIGS. 3B and 3C. It is preferable that the size be smaller than that of the second photoelectric conversion element 902. Further, in order to make the electric field applied to the first photoelectric conversion element 901 substantially uniform, the contact plug 317 for connecting the impurity semiconductor layer 319 of the first photoelectric conversion element 901 and the conductive layer 315 is connected to the substrate 310. It is preferable that the first photoelectric conversion element 901 be arranged at substantially the center in plan view. In addition, the contact plug 317 connected to the impurity semiconductor layer 319 of the first photoelectric conversion element may be formed using the same material as the impurity semiconductor layer 319 of the first photoelectric conversion element. The scintillators 904 and 905 can be formed using a material such as GOS (gadolinium oxysulfide) or CsI (cesium iodide). These materials can be formed by bonding, printing, vapor deposition, or the like. The scintillator 904 and the scintillator 905 may use the same material, or may use different materials depending on the energy of radiation to be acquired.

  In the present embodiment, the photoelectric conversion element S is an example using a PIN photodiode, but is not limited thereto. The photoelectric conversion element S may be, for example, a pn type photodiode.

  Next, the arrangement of the light shielding layer 903 that is disposed in the second photoelectric conversion element 902 and blocks light incident from the scintillator 905 will be described.

  3A, the second photoelectric conversion element 902 of the pixel PIXB includes a conductive layer 318, a semiconductor layer 320, and an upper electrode that form a lower electrode from the incident surface side of the substrate 310 toward the scintillator 904. , And a conductive layer 322 constituting the structure. The conductive layer 318 constituting this lower electrode functions as the light shielding layer 903. Specifically, the contact plug 317 and the conductive layer 318 are made of a metal material that is opaque to light emitted from the scintillator 905, such as Al, Mo, Cr, or Cu, and is disposed between the scintillator 905 and the semiconductor layer 320. To do. Thus, the conductive layer 318 functions as the light shielding layer 903. In other words, the second photoelectric conversion element 902 of the pixel PIXB is disposed between the scintillator 905 and the second photoelectric conversion element 902 so that the amount of light that can be received from the scintillator 905 is smaller than that of the first photoelectric conversion element 901. A light shielding layer 903 is disposed on the surface. Further, the second photoelectric conversion element 902 of the pixel PIXB is arranged to receive light from the scintillator 904, similarly to the first conversion element photoelectric conversion element 901 of the pixel PIXA. As a result, signals having different energy components can be acquired between the adjacent pixels PIXA and PIXB.

  3C, the first photoelectric conversion element 901 of the pixel PIXD includes the impurity semiconductor layer 319, the semiconductor layer 320, the impurity semiconductor layer 321, and the upper electrode from the incident surface side of the substrate 310. The conductive layer 322 and the electrode layer 325 are included in this order. The conductive layer 322 constituting this upper electrode functions as the light shielding layer 903. Specifically, the conductive layer 322 is made of a metal material that is opaque to light emitted from the scintillator 904, such as Al, Mo, Cr, or Cu, and is disposed between the scintillator 904 and the semiconductor layer 320, The conductive layer 3318 functions as the light-blocking layer 903. In other words, the first photoelectric conversion element 901 of the pixel PIXD has a space between the scintillator 904 and the first photoelectric conversion element 901 so that the amount of light that can be received from the scintillator 904 is smaller than that of the second photoelectric conversion element 902. A light shielding layer 903 is disposed on the surface. Also, the first photoelectric conversion element 901 of the pixel PIXD is arranged to receive light from the scintillator 905, similarly to the first photoelectric conversion element 901 of the pixel PIXA. On the other hand, in the photoelectric conversion element S, a material transparent to light emitted from the scintillator 904 such as ITO (indium tin oxide) is used for the electrode layer 325. As a result, signals having different energy components can be acquired between the adjacent pixel PIXA or the pixel PIXC or the pixel PIXD and the pixel PIXB.

  When the light from the scintillator 905 is blocked as in the pixel PIXB shown in FIGS. 3A and 3B, the switch elements T and column signal lines of the pixels PIXA and PIXC that receive the light from the scintillator 905 are used. The position of Sig may be arranged close to the pixel PIXB side. With such an arrangement, the aperture ratio of the first photoelectric conversion element 901 to the scintillator 905 can be increased in the pixel PIXA and the pixel PIXC.

  Further, the light shielding layer 903 does not need to completely shield the light from the scintillator 904 or the scintillator 905 to the photoelectric conversion element S as described above. Energy subtraction is possible if the amount of light received from the scintillator 904 or scintillator 905 on the side where the light shielding layer 903 is arranged is different between the adjacent pixel PIXA or pixel PIXC and the pixel PIXB. In such a case, it is determined in advance how much light is incident on the second photoelectric conversion element 902 of the pixel PIXB with respect to the light received by the first photoelectric conversion element 901 of the pixel PIXA, the pixel PIXC, or the pixel PIXC. Check it out. Based on this, correction can be performed by performing difference processing based on the output of the first photoelectric conversion element 901.

  As shown in FIG. 3, in the orthogonal projection with respect to the incident surface of the substrate 310, each column signal line Sig is arranged so as to overlap a part of the pixel PIX. Such a configuration is advantageous in that the area of the photoelectric conversion element S of each pixel PIX is increased, but on the other hand, the capacitive coupling between the column signal line Sig and the photoelectric conversion element S is increased. It is disadvantageous. When radiation is incident on the photoelectric conversion element S, electric charges are accumulated in the photoelectric conversion element S, and the potential of the conductive layer 318 that is the lower electrode changes, the column is connected by capacitive coupling between the column signal line Sig and the photoelectric conversion element S. Crosstalk in which the potential of the signal line Sig changes occurs. 4A to 4C show a method for dealing with this crosstalk. In the photoelectric conversion elements S arranged in the row direction intersecting the column direction among the plurality of photoelectric conversion elements S, the number of pixels PIX having the second photoelectric conversion elements 902 in which the included light shielding layers 903 are arranged is determined for each row. Arrange them to be the same. In addition, in the photoelectric conversion elements S arranged in the column direction among the plurality of photoelectric conversion elements S, the pixels PIX having the plurality of second photoelectric conversion elements 902 included are arranged so as to be the same for each column. By arranging in this way, occurrence of artifacts due to crosstalk in units of rows and columns can be suppressed.

  Further, the radiation imaging apparatus 210 may have a function of automatically detecting the start of radiation irradiation. In this case, for example, the gate line Vg is operated so that the switch element T is turned on / off, a signal from the photoelectric conversion element S is read, and the presence / absence of radiation irradiation is determined from the output signal. When the number of pixels PIX having the second photoelectric conversion elements 902 including the light shielding layer 903 is different for each row, the amount of signal output for each row is changed, and the detection accuracy varies. For this reason, as shown in FIGS. 4A to 4C, in the photoelectric conversion elements S arranged in the row direction intersecting the column direction among the plurality of photoelectric conversion elements S, the light shielding layer 903 included is arranged. The number of pixels PIX having two photoelectric conversion elements 902 is arranged to be the same for each row. With such an arrangement, the detection accuracy for automatically detecting the start of radiation irradiation is stabilized.

  In addition, the arrangement example of the pixels PIX in FIG. 4B reduces the density of the pixels PIX having the first photoelectric conversion elements 901 as compared with the arrangement example of the pixels PIX in FIG. Since the light from the scintillator 905 enters the photoelectric conversion element S through the substrate 310, the light diffuses depending on the thickness of the substrate 310, and MTF (Modulation Transfer Function) decreases. For this reason, even if the density of the pixel PIX having the first photoelectric conversion element 901 is reduced, the resolution is not substantially lowered. That is, when the first photoelectric conversion element 901 receives light emitted from the scintillator 905, the number of pixels PIX including the first photoelectric conversion element 901 is larger than the number of pixels PIX including the second photoelectric conversion element 902. May be less.

  Further, in order to suppress the diffusion of light from the scintillator 905 through the substrate 310 and reduce the decrease in MTF, the thickness of the substrate 310 may be reduced by mechanical polishing or chemical polishing. Further, in order to reduce the decrease in MTF, as shown in FIG. 3, an anti-scattering layer such as a louver layer or a micro lens that imparts directivity to light emitted by the scintillator between the scintillator 905 and the substrate 310. 326 may be provided. Further, in order to reduce the decrease in MTF, the resolution may be increased by a sharpening process in the image processing in the signal processing unit 241 of the computer 240. Also, as a method of matching the MTF of the low energy component due to the light from the scintillator 904 and the high energy component due to the light from the scintillator 905, in addition to increasing the resolving power, the MTF is lowered by matching the higher resolving power with the lower one. Let Thereafter, energy subtraction processing may be performed.

  Next, operations of the radiation imaging apparatus 210 and the radiation imaging system 200 will be described with reference to FIG. Here, the operation of the radiation imaging apparatus 210 having the imaging panel 212 including the pixels PIX each having 4 rows and 4 columns each including the photoelectric conversion element S illustrated in FIG. 2 will be described. The operation of the radiation imaging system 200 is controlled by the computer 240. The operation of the radiation imaging apparatus 210 is controlled by the control unit 214 under the control of the computer 240.

  First, the control unit 214 causes the drive circuit 114 and the readout circuit 113 to perform idle reading until radiation of radiation from the radiation source 230, in other words, irradiation of radiation to the radiation imaging apparatus 210 is started. In the idle reading, the driving circuit 114 sequentially drives the gate signals supplied to the gate lines Vg1 to Vg4 of each row of the pixel array 112 to the active level, and resets the dark charges accumulated in the photoelectric conversion element S. It is. Here, during idle reading, an active level reset pulse is supplied to the reset switch of the integrating amplifier 105, and the column signal line Sig is reset to the reference potential. The dark charge is a charge that is generated even though no radiation is incident on the photoelectric conversion element S.

  The control unit 214 can recognize the start of radiation emission from the radiation source 230 based on the start notification supplied from the exposure control unit 220 via the computer 240, for example. Further, as shown in FIG. 1, the radiation imaging apparatus 210 may be provided with a detection circuit 216 that detects a current flowing through the bias line Bs or the column signal line Sig of the pixel array 112. The control unit 214 can recognize the start of radiation irradiation from the radiation source 230 based on the output of the detection circuit 216.

  When the radiation is irradiated, the control unit 214 controls the switch element T to be in an opened state (off state). As a result, charges generated in the photoelectric conversion element S due to radiation irradiation are accumulated. The control unit 214 stands by in this state until radiation irradiation is completed.

  Next, the control unit 214 causes the driving circuit 114 and the reading circuit 113 to perform the main reading. In the main reading, the drive circuit 114 drives the gate signal supplied to the gate lines Vg1 to Vg4 in each row of the pixel array 112 to the active level. Then, the readout circuit 113 reads out the electric charge accumulated in the photoelectric conversion element S through the column signal line Sig, and outputs it to the computer 240 as radiation image data through the multiplexer 108, the buffer 109, and the AD converter 110.

  Next, acquisition of offset image data will be described. The photoelectric conversion element S continues to accumulate dark charges even in a state where it is not irradiated with radiation. For this reason, the control part 214 acquires offset image data by performing the same operation | movement as acquiring radiation image data, without irradiating a radiation. By subtracting the offset image data from the radiation image data, the offset component due to the dark charge can be removed.

  Next, driving for capturing a moving image will be described with reference to FIG. When capturing a moving image, a plurality of gate lines Vg are simultaneously driven to an active level in order to read out at high speed. At this time, if signals of the pixel PIX having the first photoelectric conversion element 901 and the pixel PIX having the second photoelectric conversion element 902 are output to one column signal wiring Sig, energy components cannot be separated. End up. Therefore, as shown in FIG. 6, by simultaneously setting the gate signals supplied to the gate line Vg1 and the gate line Vg3 to the active level, the photoelectric conversion element S12 that is the first photoelectric conversion element 901 and the photoelectric conversion element S32. Is output to the column signal line Sig2. At the same time, signals from the photoelectric conversion elements S11 and S31, which are the second photoelectric conversion elements 902, are output to the column signal line Sig1. By outputting the signals of the first photoelectric conversion element 901 and the second photoelectric conversion element 902 to different column signal lines Sig, energy subtraction processing can be performed.

  Next, an image processing flow in the present embodiment will be described with reference to FIG. First, in step S910, the control unit 214 performs control so as to accumulate charges generated by the photoelectric conversion element S during radiation irradiation in order to acquire radiation image data after performing the above-described idle reading. . Next, in step S911, the control unit 214 causes the drive circuit 114 and the reading circuit 113 to perform main reading, and reads out radiation image data. In step S911, radiation image data is output to the computer 240. Next, the control unit 214 performs an accumulation operation for acquiring offset image data in step S912. In step 913, the control unit 214 causes the drive circuit 114 and the readout circuit 113 to read the offset image data, and causes the computer 240 to output the offset image data.

  Next, the signal processing unit 241 of the computer 240 performs offset correction by subtracting the radiation image data acquired in step S911 by the offset image data acquired in step S913. Next, in step S <b> 915, the signal processing unit 241 performs the radiation image data after the offset correction, the radiation image data output from the first photoelectric conversion element 901, and the radiation output from the second photoelectric conversion element 902. Separate into image data. Here, in the configuration of FIG. 3A, the second photoelectric conversion element 902 is irradiated with radiation from the top in the drawing, light from the scintillator 904 is blocked, and is generated by high-energy radiation from the scintillator 905. A description will be given assuming that light is received. The radiation image data output from the first photoelectric conversion element 901 is referred to as double-sided image data, and the radiation image data output from the second photoelectric conversion element 902 is referred to as single-sided image data.

  Next, in step S916, the signal processing unit 241 performs the gain correction of the double-sided image data using the gain correction image data captured without the subject. In step S917, the signal processing unit 241 performs gain correction of the double-sided image data using the gain correction image data.

  After performing the gain correction, in step S918, the signal processing unit 241 detects the missing double-sided image data of the pixel PIX that does not include the first photoelectric conversion element 901, in other words, the pixel PIX that includes the second photoelectric conversion element 902. Perform pixel interpolation to compensate. Similarly, in step S919, the signal processing unit 241 performs pixel interpolation to compensate for missing single-sided image data of the pixel PIX that does not include the second photoelectric conversion element 902, in other words, the pixel PIX that includes the first photoelectric conversion element 901. I do. The pixel interpolation in steps S918 and S919 will be described with reference to FIG. Here, an example of the arrangement shown in FIG. 4B when the number of pixels PIX including the first photoelectric conversion element 901 is larger than the number of pixels PIX including the second photoelectric conversion element 902 will be described.

  First, pixel interpolation of double-sided image data will be described with reference to FIG. The double-sided image data of the pixel E having the second photoelectric conversion element 902 that outputs single-sided image data is the pixels A, B, C, and the like that have the first photoelectric conversion element 901 that outputs double-sided image data adjacent to the pixel E. Interpolation is performed using double-sided image data of D, F, G, H, and I. For example, the signal processing unit 241 may interpolate the double-sided image data of the pixel E using an average value of double-sided image data of 8 pixels adjacent to the pixel E. Further, for example, the signal processing unit 241 may interpolate the double-sided image data of the pixel E using the average value of the double-sided image data of some adjacent pixels such as the pixels B, D, F, and H. . In step S918, by performing pixel interpolation, radiation image data generated by the high energy component and low energy component of the radiation of each pixel PIX is generated.

  Next, pixel interpolation of single-sided image data will be described with reference to FIG. The single-sided image data of the pixel J having the first photoelectric conversion element 901 that outputs double-sided image data is the pixels K, L, M, and the like that have the second photoelectric conversion element 902 that outputs single-sided image data adjacent to the pixel J. Interpolation is performed using N single-sided image data. For example, the signal processing unit 241 may interpolate the single-sided image data of the pixel J using the average value of the single-sided image data of four pixels adjacent to the pixel J. In this case, for example, the distance from the position where the pixel J is arranged to the pixel K and the distance to the pixel N are different. Therefore, the single-sided image data output from the pixels K, L, M, and N may be weighted and averaged according to the distance. In step S919, by performing pixel interpolation, radiation image data generated by the high energy component of the radiation of each pixel PIX is generated.

  Next, in step S920, the signal processing unit 241 generates radiation image data based on a low energy component of radiation. As described above, when the light shielding layer 903 is provided on the radiation incident side of the second photoelectric conversion element 902, the single-sided image data is radiation image data based on a high energy component. The double-sided image data is radiation image data having both high energy and low energy components. For this reason, the radiation image data of a low energy component can be produced | generated by subtracting the single-sided image data by which pixel storage was carried out from the double-sided image data by which the pixel interpolation was carried out.

  Further, when the light shielding layer 903 is provided on the side opposite to the side on which the radiation of the second photoelectric conversion element 902 is incident, the single-sided image data becomes radiation image data based on a low energy component. For this reason, high-energy component radiation image data can be generated by subtracting the single-sided image data stored in the pixel from the double-sided image data subjected to pixel interpolation. However, since the radiation image by the high energy component is a radiation component that cannot be absorbed by the scintillator 904 on the side where the radiation is incident, the light amount from the scintillator 905 is smaller than the light amount from the scintillator 904. Therefore, when the single-sided image data is subtracted from the double-sided image data to generate the high-energy component radiation image data, the noise of the low-energy component radiation image data is carried on the high-energy component radiation image data. As a result, the S / N ratio of the radiation image data of the high energy component is lowered. For this reason, as shown in the above-described embodiment, the radiation incident side of the second photoelectric conversion element 902 is shielded, the double-sided image data is a high energy component + low energy component, and the single-sided image data is a high energy component. Let it be image data. Then, the S / N ratio can be improved by subtracting the single-sided image data from the double-sided image data to generate a low energy image.

  In step S922, the signal processing unit 241 generates an energy subtraction image. Specifically, the signal processing unit 241 determines the difference between the signal output from the first photoelectric conversion element 901 and the signal output from the second photoelectric conversion element 902 acquired in step S920, and the second photoelectric conversion element. The difference from the signal output from the conversion element 902 is taken. As a result, an energy subtraction image that is the difference between the high-energy component radiation image data and the low-energy component radiation image data is generated.

  Further, the signal processing unit 241 may generate a normal radiation image that does not perform energy subtraction in step S920 based on the double-sided image data output from the first photoelectric conversion element 901 in step S918. The first photoelectric conversion element 901 receives light from the scintillator 904 on the radiation incident side and light from the scintillator 905 on the opposite side to the radiation incident side. Thus, a higher S / N ratio can be obtained in a normal radiographic image than when only light emitted by one scintillator is received.

  Here, as shown in Patent Document 1, in order to generate one pixel data of the radiation image, only the light of the scintillator on the opposite side to the photoelectric conversion element that receives only the light of the scintillator on the radiation incident side is used. Consider a radiation imaging apparatus having a photoelectric conversion element for receiving light. A difference between the two signals output from the two photoelectric conversion elements is taken to generate an energy subtraction image, and a normal radiation image can be generated by adding the two signals. However, since two photoelectric conversion elements are required to generate one pixel data, the structure becomes complicated and the manufacturing cost may increase. In addition, the size of each photoelectric conversion element may be reduced, and the S / N ratio of the obtained signal may be reduced. In addition, when generating a normal radiographic image, when two signals are added, noise superimposed on each signal is also added, which may reduce the S / N ratio. On the other hand, in the present embodiment, a light shielding layer 903 for blocking light from the scintillator 904 or the scintillator 905 is disposed only in some of the pixels PIX including the second photoelectric conversion element 902 among the plurality of pixels PIX. The That is, since it is only necessary to add the light shielding layer 903 to some of the pixels PIX, the structure is not complicated, and a radiation imaging apparatus that can acquire an energy subtraction image while suppressing the manufacturing cost can be realized. In addition, since the first photoelectric conversion element 901 receives light emitted from the scintillator 904 and the scintillator 905, sensitivity to incident radiation can be improved, and as a result, the image quality of the obtained radiation image can be improved. Further, when generating a normal radiographic image, a radiographic image is generated from a signal generated by receiving light emitted from the two scintillators 904 and 905. For this reason, compared with a structure like patent document 1, the S / N ratio at the time of image | photographing a normal radiographic image improves.

  In the present embodiment, radiation images of radiation having two different energy components can be recorded with one radiation irradiation (one-shot method) on a subject using one imaging panel 212. For this reason, compared with the radiation imaging device which produces | generates an energy subtraction image using two imaging panels, the number of parts of a radiation imaging device decreases and manufacturing cost can be reduced. Further, since the weight of the radiation imaging apparatus 210 can be reduced, a radiation imaging apparatus that is easy to use for a portable user can be realized. In addition, since the energy subtraction image is generated by one imaging panel, a radiation imaging apparatus that does not cause the problem of positional deviation between the photoelectric conversion elements between the two imaging panels can be realized. Furthermore, it is possible to realize a radiation imaging apparatus capable of generating a radiation image with a high S / N ratio in generating not only an energy subtraction image but also a normal radiation image.

  As mentioned above, although embodiment which concerns on this invention was shown, it cannot be overemphasized that this invention is not limited to these embodiment, In the range which does not deviate from the summary of this invention, embodiment mentioned above can be changed and combined suitably. Is possible.

210 Radiation Imaging Device 310 Substrate 901 First Photoelectric Conversion Element 902 Second Photoelectric Conversion Element 903 Light Shielding Layer 904, 905 Scintillator

Claims (16)

A substrate that transmits light in which a plurality of photoelectric conversion elements are arranged in a two-dimensional array on the first surface side; a first scintillator that is disposed so as to sandwich the substrate and the plurality of photoelectric conversion elements; A radiation imaging apparatus comprising: a second scintillator disposed on a second surface side of the substrate opposite to the first surface;
The plurality of photoelectric conversion elements include a first photoelectric conversion element and a second photoelectric conversion element,
The second photoelectric conversion element includes, in order from the substrate side, a metal conductive layer functioning as a first electrode, an impurity semiconductor layer, a semiconductor layer, and a second electrode.
The first photoelectric conversion element includes, in order from the substrate side, an impurity semiconductor layer that functions as a first electrode without a metal conductive layer, a semiconductor layer, and a second electrode. A radiation imaging apparatus.   The radiation imaging apparatus according to claim 1, wherein the plurality of first photoelectric conversion elements have an area smaller than that of the second photoelectric conversion element in a plan view of the substrate. A plurality of switch elements provided corresponding to each of the plurality of photoelectric conversion elements;
A contact plug that electrically connects one switch element of the plurality of switch elements and the first photoelectric conversion element is disposed at a substantially center of the photoelectric conversion element in a plan view to the substrate, The radiation imaging apparatus according to claim 1, wherein the radiation imaging apparatus is made of the same material as the impurity semiconductor layer.   The radiation imaging apparatus according to claim 1, wherein the first photoelectric conversion element and the second photoelectric conversion element are PIN photodiodes.   The radiation imaging apparatus according to claim 1, wherein an anti-scattering layer is disposed between the second scintillator and the second surface.   The radiation imaging apparatus according to claim 1, wherein a light shielding layer is disposed between the semiconductor layer of the first photoelectric conversion element and the first scintillator.   The radiation imaging apparatus according to claim 1, wherein radiation is incident from a side of the first surface.   The radiation imaging apparatus according to claim 1, wherein radiation is incident from a side of the second surface. The radiation imaging apparatus further includes a plurality of signal lines along a column direction for outputting signals generated by the plurality of photoelectric conversion elements,
2. The photoelectric conversion elements arranged in a row direction intersecting with the column direction among the plurality of photoelectric conversion elements, the number of the plurality of second photoelectric conversion elements included is the same for each row. The radiation imaging apparatus of any one of thru | or 8.   The radiation imaging according to claim 9, wherein, in the photoelectric conversion elements arranged in the column direction among the plurality of photoelectric conversion elements, the number of the plurality of second photoelectric conversion elements included is the same for each column. apparatus. The radiation imaging apparatus further includes a plurality of signal lines along a column direction for outputting signals generated by the plurality of photoelectric conversion elements,
9. The photoelectric conversion element arranged in the column direction among the plurality of photoelectric conversion elements, wherein the number of the plurality of second photoelectric conversion elements included is the same for each column. The radiation imaging apparatus according to item 1.   The radiation imaging apparatus according to claim 1, wherein the number of the plurality of second photoelectric conversion elements is smaller than the number of the plurality of first photoelectric conversion elements. The radiation imaging apparatus according to any one of claims 1 to 12,
A radiation imaging system comprising: a signal processing unit that processes a signal from the radiation imaging apparatus.   The signal processing unit generates an energy subtraction image based on a signal output from each of the plurality of first photoelectric conversion elements and a signal output from each of the plurality of second photoelectric conversion elements. The radiation imaging system according to claim 13.   The signal processing unit includes a difference between a signal output from each of the plurality of first photoelectric conversion elements and a signal output from each of the plurality of second photoelectric conversion elements, and the second photoelectric conversion. The radiation imaging system according to claim 13 or 14, wherein an energy subtraction image is generated based on a difference between the signal output from each of the elements.   The radiation imaging system according to claim 13, wherein the signal processing unit generates a normal radiation image based on a signal output from each of the plurality of first photoelectric conversion elements.

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