JP2010087003A - Radiograph detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiograph detector equipped with a semiconductor layer, wherein both a function of preventing crystallization of a semiconductor layer and a function for blocking injection of electric charges into the semiconductor layer are sufficiently provided. <P>SOLUTION: The radiograph detector 10 is a laminate having a voltage applied electrode 1 to which a voltage is applied, a semiconductor layer 5 which generates an electric charge upon receiving radiation, and a detecting electrode 8 for detecting an electric signal corresponding to a dose in this order. The audiograph detector 10 is a laminate having an electric charge injection blocking layer 2 which blocks injection of electric charges into the semiconductor layer 5 from the voltage applied electrode 1, and a crystallization suppressing layer 4 for suppressing crystallization of the semiconductor layer 5 in this order from the voltage applied electrode 1 side between the voltage applied electrode 1 and the semiconductor layer 5. Here, a pure a-Se layer 3 with a thickness of 0.01-0.5 μm is provided between the electric charge injection blocking layer 2 and the crystallization suppressing layer 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiological image detector that records a radiographic image by generating electric charge upon irradiation with radiation and accumulating the electric charge.

  2. Description of the Related Art Conventionally, in the medical field and the like, various radiological image detectors that record a radiographic image related to a subject by irradiation with radiation that has passed through the subject have been proposed and put into practical use.

  As the radiation image detector, for example, there is a radiation image detector using amorphous selenium that generates an electric charge when irradiated with radiation. As such a radiation image detector, a so-called optical reading type or TFT (thin film) is used. An electric reading type using a transistor, a thin film transistor (CCD), a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS) sensor, or the like has been proposed.

  As an optical reading type radiographic image detector, for example, as shown in FIG. 14, the first electrode layer 101 that transmits the radiation carrying the radiographic image and the irradiation of the radiation that has transmitted the first electrode layer 101 are received. Among the charges generated in the recording photoconductive layer 102, the charge generated in the recording photoconductive layer 102 acts as an insulator, and the charge in the other polarity A charge transport layer 103 that acts as a conductor, a photoconductive layer 104 for reading that generates charges when irradiated with reading light, a transparent linear electrode 106 that transmits the reading light, and a light-shielding linear electrode that blocks the reading light A structure in which a second electrode layer composed of 107 is laminated in this order has been proposed.

  When a radiographic image is recorded on the above-described optical reading type radiographic image detector, first, in a state where a negative voltage is applied to the first electrode layer 101 of the radiographic image detector by a high-voltage power source, the subject is Radiation that passes through and carries a radiographic image of the subject is irradiated from the first electrode layer 101 side of the radiographic image detector.

  The radiation applied to the radiation image detector passes through the first electrode layer 101 and is applied to the recording photoconductive layer 102. Then, a charge pair is generated in the recording photoconductive layer 102 by the irradiation of the radiation, and the positive charge is combined with the negative charge charged in the first electrode layer 101 and disappears, and the negative charge is a latent image. A radiographic image is recorded by being accumulated in the power storage unit 105 formed at the interface between the recording photoconductive layer 102 and the charge transport layer 103 as charges (see FIG. 14).

  Next, in a state where the first electrode layer 101 is grounded, the reading light is irradiated from the second electrode layer side, and the reading light passes through the transparent linear electrode 106 and reaches the reading photoconductive layer 104. Irradiated. The positive charge generated in the reading photoconductive layer 104 by irradiation of the reading light is combined with the latent image charge in the power storage unit 105, and the negative charge is charged to the transparent linear electrode 106 and the light shielding linear electrode 107. The current flowing when coupled with the charge is detected by a charge amplifier connected to the light shielding linear electrode, and the image signal corresponding to the radiation image is read.

  However, when the first electrode layer 101 is grounded for reading out the image signal after the radiographic image is recorded in the radiographic image detector as described above, the first is caused by the influence of the electrons accumulated in the power storage unit 105. Holes are injected from the electrode layer 101 into the recording photoconductive layer 102, and this hole injection causes noise to be mixed into the read image signal, and the image quality of the read radiographic image deteriorates (see FIG. 14).

  On the other hand, as a radiographic image detector using TFTs in the electric reading method, for example, an upper electrode to which a bias voltage is applied, a semiconductor layer that generates charges upon irradiation with radiation, and charges generated in the semiconductor layers are used. An active matrix substrate in which a plurality of pixels each having a pixel electrode to be collected, a storage capacitor for storing the charge collected by the pixel electrode, and a TFT switch for reading out the charge stored in the storage capacitor are two-dimensionally arranged is stacked. What has been proposed is proposed.

  When a radiographic image is recorded on the radiographic image detector using the TFT as described above, first, a positive voltage is applied to the upper electrode of the radiographic image detector by the voltage source, and the object is transmitted. The radiation carrying the radiographic image of the subject is emitted from the upper electrode side of the radiographic image detector.

  And the radiation irradiated to the radiographic image detector permeate | transmits an upper electrode, and is irradiated to a semiconductor layer. Then, a charge pair is generated in the semiconductor layer by irradiation of the radiation, and the negative charge is combined with the positive charge charged on the upper electrode and disappears, and the positive charge is latent image charge as each pixel of the active matrix substrate. Are collected in each pixel electrode and accumulated in each accumulation capacitor to record a radiographic image.

  Then, the TFT switch of the active matrix substrate is turned on in response to the control signal output from the gate driver, the charge stored in the storage capacitor is read out, and the charge signal is detected by the charge amplifier to produce a radiographic image. The corresponding image signal is read.

  However, even in a radiographic image detector using a TFT, when a positive voltage is applied to the upper electrode as described above, holes are injected from the upper electrode into the semiconductor layer by this voltage application. Then, even after the radiation irradiation is stopped, holes are injected from the upper electrode, the holes are detected as an afterimage current, noise is mixed in the read image signal, and the image quality of the read radiation image Will deteriorate.

Patent Documents 1 and 2 also propose radiation image detectors using amorphous selenium. In the radiation image detectors described in these documents, amorphous selenium is applied from an electrode to which a voltage is applied. In order to prevent charges from being injected into the layer, it has been proposed to provide a charge injection blocking layer formed from Sb ₂ S ₃ between the electrode and the amorphous selenium layer.

  On the other hand, in the radiation image detector using amorphous selenium as described above, there is a problem that amorphous selenium is crystallized due to heat at the time of forming the electrode or contact with the electrode.

Therefore, for example, Patent Document 3 proposes a radiation image detector in which an anti-crystallization layer made of amorphous selenium containing As is provided between an electrode and an amorphous selenium layer.
JP 2001-284628 A JP 2001-177140 A JP 2008-78597 A

  Here, in order to solve both the problem of charge injection and the problem of crystallization of amorphous selenium as described above, both a charge injection blocking layer and a crystallization prevention layer are provided between the electrode and amorphous selenium. However, it has been experimentally found that the charge injection blocking function of the charge injection blocking layer is lowered when the As concentration is increased in order to obtain a sufficient anticrystallization function of the crystallization blocking layer. That is, it has been found that it is difficult to sufficiently obtain both the crystallization prevention function and the charge injection prevention function.

  An object of this invention is to provide the radiographic image detector which can fully obtain both a crystallization prevention function and a charge injection prevention function in view of said situation.

  The first radiation image detector according to the present invention includes a voltage application electrode to which a voltage is applied, a semiconductor layer that generates a charge when irradiated with radiation, and a detection electrode that detects an electrical signal corresponding to the radiation dose. A radiation image detector, which is sequentially stacked, and suppresses crystallization of a charge injection blocking layer and a semiconductor layer, which block charge injection from the voltage application electrode to the semiconductor layer between the voltage application electrode and the semiconductor layer. In the radiation image detector in which the crystallization suppressing layer is laminated in this order from the voltage application electrode side, a pure a having a thickness of 0.01 μm or more and 0.5 μm or less between the charge injection blocking layer and the crystallization suppressing layer. -Se layer is provided.

  The second radiation image detector of the present invention includes a voltage application electrode to which a voltage is applied, a semiconductor layer that generates charges upon irradiation of radiation, and a detection electrode that detects an electrical signal corresponding to the radiation dose. Radiation image detectors stacked in order, between the semiconductor layer and the detection electrode, a crystallization suppression layer that suppresses crystallization of the semiconductor layer and a charge injection block that blocks injection of charge from the detection electrode to the semiconductor layer In the radiation image detector in which the layers are laminated in this order from the semiconductor layer side, a pure a-Se layer having a thickness of 0.01 μm or more and 0.5 μm or less is provided between the charge injection blocking layer and the crystallization suppressing layer. It is provided.

  In the first and second radiographic image detectors of the present invention, the thickness of the pure a-Se layer can be 0.01 μm or more and 0.3 μm or less.

  Further, the thickness of the pure a-Se layer can be 0.01 μm or more and 0.1 μm or less.

  In addition, the voltage application electrode may be applied with a negative voltage when irradiated with radiation and grounded when reading an electric signal.

  Moreover, a positive voltage can be applied to the voltage application electrode during radiation irradiation.

  Here, the “pure a-Se layer” refers to a layer formed of a-Se in which impurities such as As are 1% or less.

  According to the first and second radiological image detectors of the present invention, a pure a-Se layer having a thickness of 0.01 μm or more and 0.5 μm or less is provided between the charge injection blocking layer and the crystallization suppressing layer. Thus, the pure a-Se layer can improve the charge injection blocking function, and both the crystallization prevention function and the charge injection blocking function can be sufficiently obtained. In addition, since the thickness is 0.01 μm or more and 0.5 μm or less, the pure a-Se layer itself can be prevented from being crystallized.

  In the first and second radiation image detectors of the present invention, the thickness of the pure a-Se layer is 0.01 μm or more and 0.3 μm or less, more preferably 0.01 μm or more and 0.1 μm or less. In this case, the crystal of the pure a-Se layer itself can be further suppressed.

  Hereinafter, a first embodiment of a radiation image detector of the present invention will be described with reference to the drawings. The radiation image detector of the first embodiment is a so-called optical reading radiation image detector. FIG. 1 is a perspective view of the radiation image detector, and FIG. 2 is a cross-sectional view of the radiation image detector shown in FIG.

  As shown in FIGS. 1 and 2, the radiation image detector 10 according to the first embodiment of the present invention is described later from a first electrode layer 1 and a first electrode layer 1 that transmit radiation carrying a radiation image. A hole injection blocking layer 2 for blocking injection of holes into the recording photoconductive layer 5, a pure a-Se layer 3, and a crystallization preventing layer 4 for preventing crystallization of the recording photoconductive layer 5. And the recording photoconductive layer 5 that generates charges when irradiated with radiation transmitted through the first electrode layer 1, and the charge of one polarity among the charges generated in the recording photoconductive layer 5 is A charge transport layer 6 that acts as an insulator and acts as a conductor for the other polarity charge, a reading photoconductive layer 7 that generates charges when irradiated with reading light, and a second electrode The layer 8 is laminated in this order. In the vicinity of the interface between the recording photoconductive layer 5 and the charge transport layer 6, a power storage unit 9 that accumulates charges generated in the recording photoconductive layer 5 is formed. In addition, although each said layer is formed in order from the 2nd electrode layer 8 on a glass substrate, the glass substrate is abbreviate | omitted in FIG. 1 and FIG.

The first electrode layer 1 may be any material as long as it transmits radiation. For example, the first electrode layer 1 may be a Nesa film (SnO ₂ ), ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), or an amorphous light-transmitting oxide film. A certain IDIXO (Idemitsu Indium X-metal Oxide; Idemitsu Kosan Co., Ltd.) can be used with a thickness of 50 to 200 nm, and Al or Au with a thickness of 100 nm can also be used.

The hole injection blocking layer 2 is made of an alloy of Sb _x S _100-x . Sb _x S _100-x preferably has a composition ratio that satisfies 41 ≦ x ≦ 60. For example, Sb ₄₂ S ₅₈ , Sb ₄₅ S ₅₅ , Sb ₆₀ S _40, or the like can be used. The thickness of the hole injection blocking layer 2 is 0.5 μm. The thickness of the hole injection blocking layer 2 is preferably 0.25 μm or more and 3 μm or less, and more preferably 0.3 μm or more and 0.7 μm or less.

  The pure a-Se layer 3 blocks the injection of holes from the first electrode layer 1 to the recording photoconductive layer 5 in the same manner as the hole injection blocking layer 2, and the pure a-Se layer 3 is made of pure a-Se. Is formed. In addition, pure a-Se here means a-Se which impurities, such as As, are 1% or less, for example. The thickness of the pure a-Se layer 3 is preferably 0.01 μm or more and 0.5 μm or less, more preferably 0.01 μm or more and 0.3 μm or less, and further preferably 0.01 μm or more and 0.1 μm or less. is there. The reason why the thickness as described above is preferable as the thickness of the pure a-Se layer 3 will be described in detail later.

  The pure a-Se layer 3 has a lower hole injection blocking function of the hole injection blocking layer 2 when the concentration of As or the like of the crystallization blocking layer 4 is increased to improve the crystallization blocking function. In consideration of the above, it is provided to further prevent hole injection.

  The crystallization preventing layer 4 includes a-Se containing at least one element selected from the group consisting of As, Sb, and Bi, 5% to 40%, more preferably 7% to 20%, and further 9% to 15%. A layer is preferred. The thickness of the crystallization preventing layer 4 is preferably 0.7 μm or more and 1.3 μm or less.

  The recording photoconductive layer 5 only needs to generate a charge when irradiated with radiation, and is excellent in that the quantum efficiency is relatively high with respect to the radiation and the dark resistance is high. A material mainly composed of Se is used. Moreover, when using the photoconductive substance which has a-Se as a main component, it uses with what has a-Se as a main component containing alkali metals, such as Na, K, Li, and content of an alkali metal is 0.01- It is preferable to set it as 5000 ppm. The thickness is suitably 100 μm or more and 2000 μm or less. In particular, when it is used for mammography, it is preferably 150 μm or more and 250 μm or less, and when used for general photographing, it is preferably 500 μm or more and 1200 μm or less.

As the charge transport layer 6, for example, the larger the difference between the mobility of charges charged in the first electrode layer 1 during recording of a radiation image and the mobility of charges having the opposite polarity, the better (for example, 10 ^2). or more, preferably 10 ³ or higher), such as poly N- vinylcarbazole (PVK), N, N'-diphenyl -N, N'-bis (3-methylphenyl) - [1,1'-biphenyl] -4 , 4′-diamine (TPD), organic compounds such as discotic liquid crystal, or TPD polymer (polycarbonate, polystyrene, PVK) dispersion, semiconductors such as a-Se, As ₂ Se ₃ doped with 10 to 200 ppm of Cl The substance is appropriate. A thickness of about 0.2 to 2 μm is appropriate.

  The reading photoconductive layer 7 may be any material that exhibits conductivity when irradiated with reading light and erasing light. For example, a-Se, Se-Te, Se-As-Te, metal-free phthalocyanine, A photoconductive material mainly containing at least one of metal phthalocyanine, MgPc (Magnesium phtalocyanine), VoPc (phase II of Vanadyl phthalocyanine), CuPc (Cupper phtalocyanine), and the like is preferable. A thickness of about 5 to 20 μm is appropriate.

  The second electrode layer 8 includes a plurality of transparent linear electrodes 8a that transmit reading light and a plurality of light-shielding linear electrodes 8b that shield reading light. Then, as shown in FIG. 1, the transparent linear electrodes 8a and the light shielding linear electrodes 8b are alternately arranged in parallel at a predetermined interval.

  The transparent linear electrode 8a transmits reading light and is made of a conductive material. Any material may be used as long as it is as described above. For example, as with the first electrode layer 1, ITO, IZO, or IDIXO can be used. Alternatively, a metal such as Al or Cr may be used to form a thickness that allows the reading light to pass (for example, about 10 nm).

  The light shielding linear electrode 8b shields the reading light and is made of a conductive material. Any material may be used as long as it is as described above. For example, there are Cr, Mo, and W having a thickness of 100 to 300 nm. Alternatively, a light shielding layer made of a resist material may be patterned in a stripe shape in advance, and the same material as that of the transparent linear electrode may be patterned thereon in a stripe shape to function as a light shielded electrode.

  Next, the operation of recording and reading a radiation image on the radiation image detector of the first embodiment will be described.

  First, as shown in FIG. 3A, in a state where a negative voltage is applied to the first electrode layer 1 of the radiation image detector 10 by the high voltage power source 20, the subject is transmitted and a radiation image of the subject is carried. Radiation is irradiated from the first electrode layer 1 side of the radiation image detector 10.

  The radiation applied to the radiation image detector 10 passes through the first electrode layer 1 and is applied to the recording photoconductive layer 5. Then, a charge pair is generated in the recording photoconductive layer 5 by irradiation of the radiation, and the positive charge is combined with the negative charge charged on the first electrode layer 1 and disappears, and the negative charge is a latent image. A radiographic image is recorded by being accumulated in the power storage unit 9 formed at the interface between the recording photoconductive layer 5 and the charge transport layer 6 as charges (see FIG. 3B).

  Then, as shown in FIG. 4, the first electrode layer 1 is grounded. Here, at this time, since the negative charge is accumulated in the power storage unit 9 by the above-described recording operation, the first electrode layer 1 is positively charged. In the radiation image detector 10 of the present embodiment, positive charges charged in the first electrode layer 1 by the hole injection blocking layer 2 and the pure a-Se layer 3 are injected into the recording photoconductive layer 5. Is being prevented.

  Next, the reading light L1 is irradiated from the second electrode layer 8 side, and the reading light L1 passes through the transparent linear electrode 8a and is irradiated to the reading photoconductive layer 7. The positive charge generated in the reading photoconductive layer 7 by the irradiation of the reading light L1 is combined with the latent image charge in the power storage unit 9, and the negative charge is passed through the charge amplifier 30 connected to the light shielding linear electrode 8b. The light shielding linear electrode 8b is combined with a positive charge charged.

  Then, a current flows through the charge amplifier 30 due to the combination of the negative charge generated in the reading photoconductive layer 7 and the positive charge charged on the light shielding linear electrode 8b, and this current is integrated and detected as an image signal. Then, an image signal corresponding to the radiation image is read.

  Here, the radiological image detector 10 of the present embodiment corrects the positive hole injection blocking layer 2 when the concentration of As or the like of the anticrystallization layer 4 is increased to improve the anticrystallization function as described above. The pure a-Se layer 3 is provided to further prevent hole injection in consideration of a decrease in the hole injection blocking function, but the As concentration and the pure a in the crystallization prevention layer 4 are provided. The relationship with the hole injection blocking function of the Se layer 3 will be examined.

  FIG. 5 shows the relationship between the As concentration of the crystallization preventing layer 4 and the leakage current from the first electrode layer 1 to the recording photoconductive layer 5. The solid line graph shown in FIG. 5 is the result of measuring the leakage current by providing pure a-Se as in this embodiment, and the wavy line graph shown in FIG. 5 is the leakage current without providing pure a-Se. It is the result of having measured.

As can be seen from FIG. 5, when the pure a-Se layer is provided as in the present embodiment, the leakage current does not increase so much even if the As concentration of the anti-crystallization layer is increased, and generally allowed. The leak current can be suppressed to 10 pA / mm ² or less, which is a reference value of the leak current. On the other hand, when the pure a-Se layer is not provided, it can be seen that the leakage current increases as the As concentration of the anti-crystallization layer increases and becomes 10 pA / mm ² or more.

  Further, the relationship between the thickness of the pure a-Se layer 3 and the leakage current will be examined. FIG. 6 is a graph showing the result of measuring the leakage current by changing the thickness of the pure a-Se layer. As shown in the graph of FIG. 6, when the thickness of the pure a-Se layer is less than 0.01 μm, the leakage current is large. However, when the thickness is 0.01 μm or more, the leakage current decreases rapidly, and then It can be seen that the leakage current remains small as the thickness increases. However, if the pure a-Se layer is too thick, the pure a-Se layer itself may crystallize and increase the leakage current. Therefore, the preferred thickness of the pure a-Se layer is as described above. It is considered to be 0.01 μm or more and 0.5 μm or less. Further, it is more preferably 0.01 μm or more and 0.3 μm or less, and further preferably 0.01 μm or more and 0.1 μm or less.

  The reason why the thin pure a-Se layer does not crystallize is that the thin pure a-Se layer is sandwiched between the relatively hard hole injection blocking layer 2 and the crystallization preventing layer 4 to change the a-Se chain. Is suppressed, and it is presumed that it is difficult to cause crystallization accompanied by a large volume reduction.

  FIG. 7 shows the relationship between the number of imaging and the amount of leakage with respect to the radiation image detector when the pure a-Se layer is provided as in the present embodiment and when the pure a-Se layer is not provided. It is shown. That is, FIG. 7 shows the results of evaluating the durability when the pure a-Se layer is provided and when the pure a-Se layer is not provided. The graph of a of FIG. 7 shows the result when the pure a-Se layer is provided, and the graphs of b, c, and d show the result when the pure a-Se layer is not provided.

  As shown in the graph of FIG. 7a, it can be seen that when a pure a-Se layer is provided, the leak amount does not change and remains sufficiently small regardless of the increase in the number of photographing. On the other hand, as shown in the graphs b to d in FIG. 7, it can be seen that when the pure a-Se layer is not provided, the leak amount increases as the number of photographing increases.

  Here, when the reason why the leakage current from the first electrode layer to the recording photoconductive layer can be suppressed when the pure a-Se layer is provided as in this embodiment, the pure a-Se layer Details of function expression are unknown, but can be inferred as follows.

The hole injection blocking layer formed of an alloy of Sb _x S _100-x and the anti-crystallization layer made of a-Se containing As have a large number of electron traps, and are the first in recording a radiographic image. It is formed by electrons trapped in a potential gradient opposite to the electric field due to the voltage applied to the electrode, and prevents injection of holes from the first electrode layer. In this state, when the applied voltage to the first electrode layer is removed at the time of reading the radiation image, a reverse potential gradient due to the remaining trap remains, and rather, the injection of holes from the first electrode layer is promoted. It will be. In the anti-crystallization layer composed of a-Se containing As, the number of electron traps is larger than that of hole traps, and the balance of the trap amount of electrons and holes deteriorates as the concentration of As increases. It is presumed that the current will increase. In addition, in the hole injection blocking layer made of Sb _x S _100-x, it is considered that the balance of traps of both charges can be controlled by the Sb composition, thereby suppressing the hole leakage current. It is easily affected by variations and it is difficult to stabilize the performance.

On the other hand, as shown in the schematic diagram of the energy band diagram shown in FIG. 8B, since the pure a-Se layer has a relatively large band gap, hole injection composed of Sb _x S _100-x. It can be inferred that the injected charge amount can be further reduced by the work function difference from the blocking layer, which contributes to the improvement of the charge injection blocking performance. FIG. 8A is a schematic diagram of an energy band diagram when no pure a-Se layer is provided.

  In the radiation image detector 10 of the first embodiment, the hole injection blocking layer 2, the pure a-Se layer 3, and the crystal are provided between the first electrode layer 1 and the recording photoconductive layer 5. Although the anti-crystallization layer 4 is provided, the problem of crystallization also occurs in the reading photoconductive layer 7, and a negative voltage is applied to the first electrode layer 1 when the radiation image is recorded, and the second electrode layer 8. Injection of holes into the reading photoconductive layer 7 may also occur, so that the reading is performed between the reading photoconductive layer 7 and the second electrode layer 8 as in the radiographic image detector 15 shown in FIG. The anti-crystallization layer 13, the pure a-Se layer 12, and the hole injection blocking layer 11 may be provided in this order from the photoconductive layer 7 side. In addition, about the component of each layer other than a layer structure, it is the same as that of the radiographic image detector 10 mentioned above.

  Further, a hole injection blocking layer 2, a pure a-Se layer 3 and a crystallization preventing layer 4 are provided between the first electrode layer 1 and the recording photoconductive layer 5, and the reading photoconductive layer 7 and Between the second electrode layer 8, an anti-crystallization layer 13, a pure a-Se layer 12, and a hole injection blocking layer 11 may be provided in this order from the reading photoconductive layer 7 side.

  In the description of the first embodiment, the radiation image detector is described in which a negative voltage is applied as a bias voltage to the first electrode layer. However, a positive voltage is applied to the first electrode layer as a bias voltage. The radiation image detector may also be provided with the pure a-Se layer of the present invention.

  However, in that case, an electron injection blocking layer is provided instead of the hole injection blocking layer. That is, an electron injection blocking layer, a pure a-Se layer, and a crystallization preventing layer are provided between the first electrode layer and the recording photoconductive layer, and between the reading photoconductive layer and the second electrode layer. In addition, an anti-crystallization layer, a pure a-Se layer, and an electron injection blocking layer may be provided in this order from the reading photoconductive layer side.

Examples of the electron injection blocking layer include Sb ₂ S ₃ and organic compounds.

  Next, a second embodiment of the radiation image detector of the present invention will be described. The radiation image detector according to the second embodiment is a radiation image detector using a TFT. FIG. 10 is a partial cross-sectional view of the radiation image detector according to the second embodiment.

  As shown in FIG. 10, the radiation image detector 50 according to the second embodiment includes an active matrix substrate 60 and a radiation detection unit 70 stacked on the active matrix substrate 60.

  The radiation detector 70 includes a semiconductor layer 75 formed on substantially the entire surface of the active matrix substrate 60, a crystallization preventing layer 74 provided on the semiconductor layer 75, a pure a-Se layer 73, and hole injection blocking. A layer 72 and an upper electrode 71 are provided.

  The semiconductor layer 75 has electromagnetic wave conductivity, and generates electric charges inside the film when irradiated with X-rays. As the semiconductor layer 75, for example, an amorphous a-Se film having a film thickness of 100 to 1000 μm whose main component is selenium can be used. The semiconductor layer 75 is formed on the active matrix substrate 60 by a vacuum deposition method.

  The upper electrode 71 is made of a low-resistance conductive material such as Au or Al.

  The crystallization preventing layer 74, the pure a-Se layer 73, and the hole injection blocking layer 72 are the same as those in the first embodiment.

  The active matrix substrate 60 includes a pixel electrode 61 that collects charges generated in the semiconductor layer 75, a storage capacitor 62 that stores charges collected by the pixel electrode 61, and a TFT switch 63 that reads charges stored in the storage capacitor 62. A plurality of pixels 64, a number of scanning wirings 65 for turning on / off the TFT switch 63, and a number of data wirings 66 for reading out the charges accumulated in the storage capacitor 62.

  As the TFT switch 63, an a-Si TFT using amorphous silicon as an active layer is generally used.

  FIG. 11 shows a plan view of the active matrix substrate 60. As shown in FIG. 11, the active matrix substrate 60 is provided with a large number of pixels 64 having storage capacitors 62 and TFT switches 63 in a two-dimensional manner, and scanning wirings 65 and data wirings 66 are arranged in a grid pattern. Has been placed. A read circuit 80 comprising an amplifier for detecting signal charges flowing out to the data line 66 is connected to the end of the data line 66, and a control signal for turning on / off the TFT switch 63 is supplied to the scan line 65. An output gate driver 90 is connected.

  Here, in the radiographic image detector of the TFT system, a positive voltage is applied to the upper electrode during recording and reading of the radiographic image. By applying this positive voltage, holes are generated from the upper electrode to the semiconductor layer. Injected. Then, even after the radiation irradiation is stopped, holes are injected from the upper electrode, the holes are detected as an afterimage current, noise is mixed in the read image signal, and the image quality of the read radiation image Will deteriorate.

  Therefore, in the radiation image detector 50 of the present embodiment, the hole injection blocking layer 72 and the pure a− are interposed between the upper electrode 71 and the semiconductor layer 75 in order to block the injection of holes from the upper electrode 71. An Se layer 73 is provided.

  Next, the operation of recording and reading a radiation image on the radiation image detector of the second embodiment will be described.

  First, as shown in FIG. 12, in a state where a positive voltage is applied to the upper electrode 71 of the radiation image detector 50 by the voltage source 55, the radiation that has passed through the subject and carries the radiation image of the subject is detected by the radiation image detector. 50 is irradiated from the upper electrode 71 side.

  The radiation applied to the radiation image detector 50 passes through the upper electrode 71 and is applied to the semiconductor layer 75. Then, a charge pair is generated in the semiconductor layer 75 by the irradiation of the radiation, and the negative charge is combined with the positive charge charged in the upper electrode 71 and disappears, and the positive charge is a latent image charge of each pixel 64. A radiation image is recorded by being collected in each pixel electrode 61 and accumulated in each storage capacitor 62.

  Then, a control signal for turning on the TFT switch 63 is sequentially output from the gate driver 90 shown in FIG. Then, the TFT switch 63 connected to each scanning wiring 65 is turned on in response to the control signal output from the gate driver 90, and the stored charge is read from the storage capacitor 62 of each pixel 64 to the data wiring 66. The charge signal flowing out to the data wiring 66 is detected as an image signal by the charge amplifier of the readout circuit 80, and the image signal is read according to the radiation image.

  The operations of the hole injection blocking layer 72 and the pure a-Se layer 73 in the radiation image detector 50 of the present embodiment are the same as those of the radiation image detector 10 of the first embodiment.

  In the radiological image detector 55 of the second embodiment, a positive voltage is applied as a bias voltage to the upper electrode 1, so that a hole injection blocking layer 72 is interposed between the upper electrode 71 and the semiconductor layer 75. Although the pure a-Se layer 73 and the crystallization preventing layer 74 are provided, the problem of crystallization also occurs between the semiconductor layer 75 and the pixel electrode 61, and electrons from the pixel electrode 61 to the semiconductor layer 75 are generated. Implantation may also occur, and therefore, like the radiographic image detector 55 shown in FIG. 13, an anti-crystallization layer 78, a pure a-Se layer 77, and a layer between the semiconductor layer 75 and the pixel electrode 61 in order from the semiconductor layer 75 side. An electron injection blocking layer 76 may be provided.

  Further, a hole injection blocking layer 72, a pure a-Se layer 73 and a crystallization preventing layer 4 are provided between the upper electrode 71 and the semiconductor layer 75, and a semiconductor is interposed between the semiconductor layer 75 and the pixel electrode 61. The crystallization preventing layer 78, the pure a-Se layer 77, and the electron injection blocking layer 76 may be provided in this order from the layer 75 side.

  In the description of the second embodiment, the radiation image detector in which a positive voltage is applied as a bias voltage to the upper electrode has been described. However, the radiation image detector in which a negative voltage is applied as a bias voltage to the upper electrode. Also, a pure a-Se layer of the present invention may be provided. However, in that case, an electron injection blocking layer is provided instead of the hole injection blocking layer. That is, an electron injection blocking layer, a pure a-Se layer, and an anti-crystallization layer are provided between the upper electrode and the semiconductor layer, and an anti-crystallization layer is sequentially formed between the semiconductor layer and the pixel electrode from the semiconductor layer side, A pure a-Se layer and a hole injection blocking layer may be provided.

In the above-described embodiment, a so-called direct conversion type radiation image detector that directly converts radiation into electric charges has been described. However, the present invention is not limited thereto, and radiation is once converted into light by a phosphor and the light is charged. The present invention can also be applied to a radiation image detector having a configuration similar to a so-called indirect conversion type radiation image detector. Note that a radiation image detector having a configuration similar to the indirect conversion type radiation image detector is more than a direct conversion type radiation image detector.
The Se layer is thinned, a light transmission type first electrode layer is provided, a phosphor is provided above the first electrode layer, and light from the phosphor is converted into electric charges. In the radiographic image detector configured as described above, the thickness of the recording photoconductive layer or the semiconductor layer is about 1 to 30 μm. In the case of an electric reading type radiographic image detector, the storage capacity is It does not have to be.

The perspective view which shows 1st Embodiment of the radiographic image detector of this invention. 2-2 sectional view of the radiation image detector shown in FIG. The figure for demonstrating the effect | action of recording of the radiographic image to the radiographic image detector of 1st Embodiment. The figure for demonstrating the effect | action of recording of the radiographic image to the radiographic image detector of 1st Embodiment. The figure for demonstrating the effect | action of reading of the radiographic image from the radiographic image detector of 1st Embodiment. Graph showing the relationship between the As concentration of the anti-crystallization layer and the leakage current from the first electrode layer to the recording photoconductive layer The graph which shows the result of having measured the leakage current by changing the thickness of a pure a-Se layer Graph showing the relationship between the number of light shots and the amount of leakage for a radiation image detector Schematic diagram of energy band diagram when no pure a-Se layer is provided Schematic diagram of energy band diagram when a pure a-Se layer is provided Sectional drawing which shows the modification of the radiographic image detector of 1st Embodiment. Partial sectional drawing of the radiographic image detector of the 2nd Embodiment of this invention Plan view of an active matrix substrate in the radiation image detector of the second embodiment The figure for demonstrating the effect | action of recording and reading of the radiographic image to the radiographic image detector of 2nd Embodiment. Sectional drawing which shows the modification of the radiographic image detector of 2nd Embodiment. Diagram for explaining hole injection in a conventional radiation image detector

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st electrode layer 2 Hole injection blocking layer 3 Pure a-Se layer 4 Crystallization prevention layer 5 Photoconductive layer for recording 6 Charge transport layer 7 Photoconductive layer for reading 8 Second electrode layer 8a Transparent linear electrode 8 b Light-shielding linear electrode 9 Power storage unit 10 Radiation image detector 11 Hole injection blocking layer 12 Pure a-Se layer 13 Anti-crystallization layer 15 Radiation image detector 50 Radiation image detector 56 Radiation image detector 60 Active matrix substrate 61 Pixel electrode 62 Storage capacitor 63 TFT switch 64 Pixel 65 Scanning wiring 66 Data wiring 70 Radiation detector 71 Upper electrode 72 Hole injection blocking layer 73 Pure a-Se layer 74 Crystallization preventing layer 75 Semiconductor layer 76 Electron injection blocking layer 77 Pure a-Se layer 78 Anti-crystallization layer

Claims (6)

A radiation image detector in which a voltage application electrode to which a voltage is applied, a semiconductor layer that generates a charge when irradiated with radiation, and a detection electrode that detects an electrical signal corresponding to the radiation dose are stacked in this order, Between the voltage application electrode and the semiconductor layer, a charge injection blocking layer that blocks injection of charges from the voltage application electrode to the semiconductor layer, and a crystallization suppression layer that suppresses crystallization of the semiconductor layer, In the radiation image detector laminated in this order from the voltage application electrode side,
A radiation image detector, wherein a pure a-Se layer having a thickness of 0.01 μm or more and 0.5 μm or less is provided between the charge injection blocking layer and the crystallization suppressing layer. A radiation image detector in which a voltage application electrode to which a voltage is applied, a semiconductor layer that generates a charge when irradiated with radiation, and a detection electrode that detects an electrical signal corresponding to the radiation dose are stacked in this order, Between the semiconductor layer and the detection electrode, a crystallization suppressing layer for suppressing crystallization of the semiconductor layer and a charge injection blocking layer for blocking charge injection from the detection electrode to the semiconductor layer are on the semiconductor layer side. In the radiation image detectors stacked in this order from
A radiation image detector, wherein a pure a-Se layer having a thickness of 0.01 μm or more and 0.5 μm or less is provided between the charge injection blocking layer and the crystallization suppressing layer.   The radiation image detector according to claim 1, wherein the pure a-Se layer has a thickness of 0.01 μm or more and 0.3 μm or less.   The radiographic image detector according to claim 1, wherein a thickness of the pure a-Se layer is 0.01 μm or more and 0.1 μm or less.   5. The radiation image detector according to claim 1, wherein a negative voltage is applied to the voltage application electrode when the radiation is irradiated, and the voltage application electrode is grounded when the electric signal is read. 6.   The radiographic image detector according to claim 1, wherein a positive voltage is applied to the voltage application electrode when the radiation is applied.

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