JP2009135212A - Radiation image detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain the electrical characteristics (dark current, defect) of a radiation detector for the long term. <P>SOLUTION: A radiation image detector is formed by laminating a bias electrode 8 for transmitting the electromagnetic wave for recording which carries an image information, a photoconductive layer 5 for recording whose main component being a-Se for generating charges by the irradiation with the electromagnetic wave for recording transmitted through the bias electrode 8, a charge accumulator for accumulating the generated charges, a plurality of reference electrodes 2, and a substrate 1 in this order. In the detector, a first intermediate layer 7 consisting of antimony sulfide, and a second intermediate layer 6 consisting of an a-Se layer containing at least one species from among an alkali metal fluoride, an alkaline earth metal fluoride, an alkali metal oxide, an alkaline earth metal oxide, SiO<SB>x</SB>, GeO<SB>x</SB>(0.5≤x≤1.5 for both x) as a specific material, are laminated and provided between the bias electrode 8 and the photoconductive layer 5 for recording so that the second intermediate layer 6 faces the photoconductive layer 5 for recording, and the average concentration of the specific material in the second intermediate layer 6 is made to be ≥0.0003 mol% and ≤0.003 mol%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiation image detector suitable for application to a radiation imaging apparatus such as an X-ray.

2. Description of the Related Art In radiography for medical diagnosis, there is known a radiation imaging apparatus that uses a radiation image detector (which mainly includes a semiconductor) that detects radiation and converts it into an electrical signal. As a radiation image detector, a direct conversion method in which radiation is directly converted into charges and accumulated, and radiation is converted into light once by a scintillator such as CsI: Tl or GOS (Gd ₂ O ₂ S: Tb). There is an indirect conversion method in which light is converted into electric charges by a photoconductive layer and accumulated. Further, from the reading method, charges generated by radiation irradiation are stored in a storage capacitor, and the stored charges are read by turning on and off an electrical switch such as a thin film transistor (TFT) one pixel at a time. A so-called optical reading method in which charges generated by radiation irradiation are stored in a power storage unit, and the stored charges are read using a semiconductor material that generates charges by light irradiation. It is roughly divided into

  The direct conversion type radiographic image detector applies a predetermined bias voltage between the bias electrode formed on the surface of the radiation-sensitive semiconductor film (recording photoconductive layer) and the reference electrode formed on the substrate. It is configured to detect the radiation by collecting the electric charge generated with the irradiation with the charge collecting electrode formed on the back surface of the semiconductor film and taking it out as a radiation detection signal. The layer is often formed of amorphous selenium (a-Se) because of the advantages of high dark resistance and excellent response speed.

  In general, a metal material having a large work function (about 5 eV) such as Au, Pt, and Pd is often used as the electrode material from the viewpoint of environmental stability. Since the work function of a-Se is about 5.8 eV and the difference from the above electrode material is small, when an electrode is formed on a-Se and a bias voltage having a positive potential is applied, a-Se is applied from the electrode. A dark current is generated by holes injected with the help of an electric field. Once injected, these extra holes contribute to a large dark current well beyond the high resistivity of a-Se.

For example, in Patent Document 1 or Patent Document 2, when an Sb ₂ S ₃ layer (0.01 to 50 μm thickness) is stacked on an a-Se layer, the correctness depends on the interface between the Se layer and the Sb ₂ S ₃ layer. It is described that the pores can be blocked. In general, a radiation image detector is provided with a hole capturing layer. For example, in Patent Document 3, a layer in which a-Se is doped with LiF is applied to a positive bias application electrode. It describes that it is provided as a hole trapping layer (thickness 0.5 to 10 μm) for trapping holes injected into the photoelectric conversion layer and reducing dark current.
JP 2001-284628 A JP 2001-177140 A JP-A-9-36341

Although the hole blocking layer described in Patent Documents 1 and 2 can satisfy initial electrical characteristics (dark current), it can maintain electrical characteristics (dark current, defects) over a long period of time. was difficult. This is because it relies holes of blocking the interface between the Se layer and Sb ₂ S ₃ layer, a slight characteristic change at a joint interface of the Se layer and Sb ₂ S ₃ layer, a hole blocking characteristics change This is considered to be easy, but for this reason, there is a problem that the dark current characteristics after repeated use temporarily deteriorate.

  On the other hand, the hole capture layer described in Patent Document 3 needs to have a LiF concentration of 0.05 to 5% in order to capture all holes injected from the electrode into the photoelectric conversion layer. Thus, when the concentration of LiF to be doped is high, crystallization is likely to occur over time, and it is difficult to maintain the quality over a long period of time.

  This is because, since the melting point of the compound dopant is generally as high as 800 ° C. or higher, the doping method using an alloy raw material in which a compound dopant is mixed with an Se raw material as a vapor deposition raw material has a low efficiency of doping the compound dopant into the vapor deposition film. Therefore, it is necessary to use a so-called co-evaporation method in which the above compound dopant is doped by vapor deposition from another vapor deposition source, and by this co-deposition, crystals are formed in the a-Se film which is the base material of the hole trapping layer. This is probably because defects such as nucleation are easily introduced.

  The present invention has been made in view of the above circumstances, and even if doping is performed by co-evaporation, thermal damage to the base a-Se film is small, electrical characteristics (dark current) after repeated use, and long-term use An object of the present invention is to provide a radiographic image detector capable of maintaining electrical characteristics (dark current, defects).

The radiation image detector of the present invention comprises a bias electrode that transmits a recording electromagnetic wave carrying image information, and a main component of a-Se that generates charges by irradiation of the recording electromagnetic wave that has passed through the bias electrode. A radiographic image detector comprising a recording photoconductive layer, a power storage unit for accumulating the generated charge, a plurality of reference electrodes, and a substrate stacked in this order, of the bias electrode or the reference electrode A first intermediate layer made of antimony sulfide between the electrode having a positive potential with respect to the power storage unit and the recording photoconductive layer when the charge of the power storage unit is read; As the substance, at least one of alkali metal fluoride, alkaline earth metal fluoride, alkali metal oxide, alkaline earth metal oxide, SiO _x , GeO _x (x is both 0.5 ≦ x ≦ 1.5) Contains seed a second intermediate layer made of an a-Se layer is provided by laminating the second intermediate layer toward the recording photoconductive layer side, and the specific intermediate concentration of the second intermediate layer is 0. It is characterized by being 0003 mol% or more and 0.003 mol% or less.

When the average concentration of the specific substance in the second intermediate layer is x (mol%) and the layer thickness of the second intermediate layer is y (μm), x · y ≧ 0.0003 and y ≦ 30. It is preferable.
The layer thickness of the second intermediate layer is preferably 1 to 30 μm.

The radiological image detector of the present invention comprises a bias electrode that transmits a recording electromagnetic wave carrying image information, and a charge that is generated by irradiation of the recording electromagnetic wave that has passed through the bias electrode. In a radiation image detector comprising a recording photoconductive layer, a power storage unit for accumulating generated charges, a plurality of reference electrodes, and a substrate stacked in this order, of the bias electrode or the reference electrode, When reading the charge, a first intermediate layer made of antimony sulfide is interposed between the electrode having a positive potential with respect to the power storage unit and the recording photoconductive layer, and an alkali metal fluoride as a specific substance. A-Se containing at least one of alkaline earth metal fluoride, alkali metal oxide, alkaline earth metal oxide, SiO _x , GeO _x (x is 0.5 ≦ x ≦ 1.5) Second consisting of layers Since the intermediate layer is provided by laminating the second intermediate layer toward the recording photoconductive layer side, dark current leakage generated only in the case of the first intermediate layer is prevented. Can capture the shortage of hole capturing ability, suppress dark current after repeated use, and stabilize electric characteristics over a long period of time.

  In particular, by providing the first intermediate layer and the second intermediate layer in a stacked manner, the specific substance average concentration of the second intermediate layer is 0.0003 mol% compared to the case where the first intermediate layer is not provided. Since the concentration can be suppressed to a low concentration of 0.003 mol% or less, crystallization hardly occurs over time, and an increase in image defects can be suppressed. In addition, by suppressing the specific substance average concentration of the second intermediate layer to a low concentration of 0.0003 mol% or more and 0.003 mol% or less, there is little thermal damage caused by the specific substance at the time of manufacture, so durability is improved. It can be set as the outstanding radiographic image detector.

The radiation image detector includes a direct conversion system that directly converts radiation into electric charge and accumulates the charge, and once converts the radiation into light by a scintillator such as CsI: Tl, GOS (Gd ₂ O ₂ S: Tb) There is an indirect conversion method in which light is converted into electric charges by a photoconductive layer such as a-Se, and the radiation image detector of the present invention is applied to the former direct conversion method and the latter indirect conversion method. It is possible. In addition to X-rays, γ rays, α rays, etc. can be used as radiation.
The radiation image detector of the present invention can be used for both the TFT method and the so-called optical reading method.

  Hereinafter, the radiation image detector of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of a radiation image detector according to an embodiment of the present invention. A radiological image detector 10 shown in FIG. 1 includes an active matrix layer 2 comprising a reading circuit comprising TFTs, a pixel electrode and a storage capacitor, an electron blocking layer 3, a crystallization preventing layer 4, and a recording photoconductive layer on a substrate 1. 5, a second intermediate layer 6, a first intermediate layer 7, and a bias electrode 8 that transmits a recording electromagnetic wave carrying image information are laminated in this order.

  An enlarged cross-sectional view of the active matrix layer 2 is shown in FIG. In the active matrix layer 2, as shown in FIG. 3, a TFT 31 and a storage capacitor 32 are formed corresponding to each pixel, and an output line of each TFT 31 is connected to a signal detection means (not shown). The control line of each TFT 31 is connected to a TFT control means (not shown). The storage capacitor 32 is formed by laminating a lower electrode 33, an insulating layer 34, an upper electrode 35, and a charge collection electrode 36 in this order on the substrate 1. Here, in the upper electrode 35 of the storage capacitor 32, a region facing the lower electrode 33 is a region where charge is induced (accumulated) and corresponds to a power storage unit. The lower electrode 33 is an electrode for providing a reference potential with respect to the bias electrode 8 and corresponds to the reference electrode.

  When the radiographic image detector 10 irradiates the recording photoconductive layer 5 with X-rays while an electric field is formed between the bias electrode 8 and the reference electrode, the radiographic image detector 10 enters the recording photoconductive layer 5. Charge pairs are generated, and latent image charges corresponding to the amount of the charge pairs are accumulated in the power storage unit in the active matrix layer 2. When reading the accumulated latent image charge, the TFTs of the active matrix layer 2 are sequentially driven to output an image signal based on the latent image charge corresponding to each pixel from the output line, and this image signal is detected. By detecting by means, the electrostatic latent image carried by the latent image charge can be read. In FIG. 1, when reading the electric charge of the power storage unit, the electrode having a positive potential with respect to the power storage unit is the bias electrode 8. Therefore, the second intermediate layer 6 and the first intermediate layer 7 are A second intermediate layer 6 is provided between the bias electrode 8 and the recording photoconductive layer 5 so as to face the recording photoconductive layer 5.

  The bias electrode 8 only needs to be transparent to X-rays. For example, a gold thin film can be used. The recording photoconductive layer 5 is mainly composed of a-Se and may be doped with an alkali metal. Here, the main component means a content of 50% or more.

As the substrate 1, glass, polyimide, polycarbonate, a flexible substrate in which an insulating thin film such as SiO ₂ is formed on a SUS metal plate having a thickness of about 0.1 mm can be used.

The electron blocking layer 3 is a layer for blocking or capturing electrons injected from the pixel electrode into the recording photoconductive layer 5 in the layer or at the layer interface, and is Sb ₂ S ₃ , As ₂ Se ₃ , As _2. An inorganic material such as S ₃ or CdSe, an organic film such as PVK or polycarbonate (PC) to which a hole transport molecule is added, or the like can be used. The thickness of the electron blocking layer is preferably about 0.05 to 5 μm.

  The crystallization preventing layer 4 is an a-Se layer containing 3 to 40%, preferably 10 to 33% of at least one element selected from the group consisting of As, Sb, and Bi, and preferably has a thickness of 0.05 to An a-Se layer of 0.3 μm or an organic film such as a polycarbonate film can be used. By providing the anti-crystallization layer, crystallization of the recording photoconductive layer 5 at the interface with the recording photoconductive layer 5 can be suppressed.

The second intermediate layer 6 includes, as specific substances, alkali metal fluorides, alkaline earth metal fluorides, alkali metal oxides, alkaline earth metal oxides, SiO _x , GeO _x (x is 0.5 ≦ x ≦ 1.5, preferably x = 1) a-Se layer containing at least one kind, and the specific substance with respect to a-Se has an average concentration of 0.0003 mol% or more and 0.003 The layer is contained in an amount of not more than mol%, more preferably not less than 0.0003 mol% and less than 0.003 mol%.

  The second intermediate layer 6 has a specific substance average concentration of 0.0003 mol% or more and 0.003 mol% or less, and the second intermediate layer has a specific substance average concentration of x (mol%) and a second intermediate layer. When the layer thickness is y (μm), it is preferable that x · y ≧ 0.0003 and y ≦ 30 be satisfied. This will be described with reference to FIG. FIG. 4 is a logarithmic graph showing the relationship between x and y. It is the shaded portion of the graph that satisfies the relationship of y ≦ 30 when x · y ≧ 0.0003 (the points in the graph are the specific substance average concentration and the layer thickness in the examples). The leakage component of the dark current is captured by the specific substance contained in the second intermediate layer. Even if the thickness of the second intermediate layer is as thin as 0.1 μm, the second intermediate layer is specified. If the substance average concentration is as high as 0.003 mol%, the absolute amount of the specific substance contained in the second intermediate layer is secured, while the specific substance average concentration in the second intermediate layer is as low as 0.0003 mol%. However, if the thickness of the second intermediate layer is as thick as 1 μm, the absolute amount of the specific substance contained in the second intermediate layer is similarly secured, and the specific substance average of the second intermediate layer is secured. By appropriately adjusting the concentration and the layer thickness, the second intermediate layer can have a specific substance necessary for capturing the dark current leakage component.

  As described above, the thickness of the second intermediate layer 6 can be appropriately selected according to the desired amount of trapped charges, but is particularly preferably in the range of 1 to 30 μm. By setting the thickness of the second intermediate layer 6 to 1 μm or more, the hole trapping function can be sufficient even if the concentration of the specific substance is about 0.0003 mol%. On the other hand, when the layer thickness of the second intermediate layer 6 is 30 μm or less, it is possible to suppress a decrease in X-ray sensitivity. The thickness of the second intermediate layer has a value of 10% of the maximum specific substance concentration in the intermediate layer by measuring the concentration distribution of the specific substance added to the Se film simultaneously formed on the substrate. It can be obtained by measuring the length of the region sandwiched between the two most distant interfaces.

  When the specific substance contained in the second intermediate layer 6 concentrates on the bonding interface with the first intermediate layer 7 or the recording photoconductive layer 5 in contact with the second intermediate layer 6, crystallization occurs at this interface over time. Is likely to occur. This is thought to be because the residual water at the interface reacts with the specific substance to isolate the alkali metal, alkaline earth metal, or Si or Ge of the specific substance. For this reason, the concentration of the specific substance in the interface region between the first intermediate layer 7 and the recording photoconductive layer 5 is 1.5 digits toward the interface between the first intermediate layer 7 and the recording photoconductive layer 5. / 1 μm or less, more preferably 0.5 to 1.5 digits / 1 μm or less. Thereby, the time for the specific substance to diffuse in a-Se and reach the interface region is extended, and the lifetime can be extended.

  In order to obtain such a concentration distribution, the vapor deposition source of Se, which is the base material of the second intermediate layer, is separated from the vapor deposition source of the specific substance contained in the second intermediate layer, and co-vapor deposition is performed simultaneously. It can be manufactured using the law. For example, it is possible to create a concentration distribution of the specific substance in the layer thickness direction by keeping the deposition rate of Se as a base material constant and appropriately controlling the deposition source temperature of the specific substance with respect to time. Further, by using the deposition source shutter and further the substrate shutter, the boundary in the layer thickness direction of the second intermediate layer is clarified, the first intermediate layer 7 adjacent to the second intermediate layer, and the recording photoconductive layer. Inhibition of function 5 can be prevented.

  The upper region, the lower region, or the entire region of the intermediate layer of the second intermediate layer 6 may be doped with As, Sb, Bi, or the like as long as the hole capturing ability is not lost.

  As shown in FIG. 1, the second intermediate layer 6 is preferably provided in direct contact with the recording photoconductive layer 5. Both the recording photoconductive layer 5 and the second intermediate layer 6 are based on a-Se, and have a high continuity of a-Se bonding at the bonding interface, and therefore have a small barrier to electron mobility. Therefore, by providing the second intermediate layer 6 in direct contact with the recording photoconductive layer 5, electrons generated inside the recording photoconductive layer 5 are converted into the recording photoconductive layer 5 and the second intermediate layer 6. Can be swept out to the electrode 8 without accumulating in the interfacial region where they contact each other.

The first intermediate layer 7 is a layer made of antimony sulfide that blocks holes and allows electrons to pass therethrough. Here, the antimony sulfide may not have a complete Sb ₂ S ₃ composition but may have a slight compositional deviation. The thickness of the first intermediate layer 7 depends on the film formation conditions of antimony sulfide, but is preferably about 0.1 to 1 μm. The antimony sulfide film functions as a hole blocking layer mainly because the interface with the second intermediate layer 6 (a-Se layer containing a specific substance) in contact with the antimony sulfide layer is an electrical barrier. It is estimated that. On the other hand, since the antimony sulfide layer itself of the first intermediate layer 7 has a strong property of having many localized levels for capturing electrons, if the layer thickness exceeds 2 μm, electrons cannot pass through the film, and a hole blocking layer. It will no longer be suitable. For this reason, the hole blocking layer is preferably 1 μm or less, particularly preferably 0.5 μm or less. On the other hand, if the film thickness is small, film peeling tends to occur. Therefore, the thickness of the first intermediate layer is preferably 0.1 μm or more.

  Also, the bias electrode is made of a material having a work function smaller than that of antimony sulfide (specifically, Au, Al), and a potential barrier is formed at the interface between the first intermediate layer and the electrode layer in contact therewith. Thus, it is preferable to further strengthen the hole blocking function of the first intermediate layer 7. In this case, if the thickness of the first intermediate layer 7 is reduced to 2 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less, the rectifying contact that prevents hole injection rather than the property as an electron blocking film is used. It has superior properties and can be used as a hole blocking layer.

  In this way, the first intermediate layer and the second intermediate layer are made of the recording conductive layer and the bias electrode (the electrode on the side having a positive potential with respect to the power storage unit when the charge of the power storage unit is read). By laminating between them, it is possible to make up for insufficient hole trapping ability when the concentration of the specific substance in the second intermediate layer is low, and to suppress dark current.

  The electron blocking layer, the crystallization preventing layer, the recording photoconductive layer, and the bias electrode can be provided by a known method such as resistance heating vapor deposition or co-evaporation.

  FIG. 2 is a schematic cross-sectional view showing a configuration of a radiation image detector according to another embodiment of the present invention. In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted unless necessary (the same applies hereinafter). The radiographic image detector 10 shown in FIG. 2 includes an active matrix layer 2 comprising a reading circuit comprising TFTs and pixel electrodes, a first intermediate layer 7, a second intermediate layer 6, and a recording photoconductive layer on a substrate 1. 5, an anti-crystallization layer 4, an electron blocking layer 3, and a bias electrode 8 that transmits electromagnetic waves for recording carrying image information are laminated in this order.

  When the radiographic image detector shown in FIG. 2 reads out the electric charge of the power storage unit, the active matrix layer 2 (the electrode on the side having a positive potential with respect to the power storage unit is composed of a reading circuit including TFTs and a storage capacitor ( In detail, the second intermediate layer 6 and the first intermediate layer 7 are disposed between the active matrix layer 2 and the recording photoconductive layer 5 between the second intermediate layer 6 and the recording photoconductive layer 5. The layer 6 is provided facing the recording photoconductive layer 5. In the case of the electrical reading method, since the photoconductive layer such as a-Se is not actually disposed on the substrate side of the charge collection electrode, the second intermediate layer 6 and the first intermediate layer 7 are connected to the reference electrode and the charge. It is not provided between the collection electrodes, and is provided between the charge collection electrode and the recording photoconductive layer 5.

  FIG. 5 is a schematic cross-sectional view showing a configuration of a so-called optical reading type radiation image detector that reads charges accumulated in a power storage region by using a semiconductor material that generates charges by light irradiation. The radiation image detector 10 shown in FIG. 5 includes a linear electrode 11 (corresponding to a reference electrode, hereinafter referred to as a reference electrode), a reading photoconductive layer 12, a power storage unit 13, a recording photoconductive layer 5, A second intermediate layer 6, a first intermediate layer 7, and a bias electrode 8 that transmits electromagnetic waves for recording carrying image information are laminated in this order. In the radiological image detector shown in FIG. 5, when the electric charge of the power storage unit is read, the electrodes on the side having a positive potential with respect to the power storage unit are the bias electrode 8 and the reference electrode 11. In FIG. 5, the second intermediate layer 6 and the first intermediate layer 7 are disposed between the bias electrode 8 and the recording photoconductive layer 5, and the second intermediate layer 6 is directed to the recording photoconductive layer 5. The aspect provided is shown. This radiographic image detector can read out a radiographic image by scanning a readout linear light source in a direction orthogonal to the linear electrode.

  In the optical reading type radiographic image detector shown in FIG. 5, the first intermediate layer and the second intermediate layer are stacked and stacked between the bias electrode 8 and the recording photoconductive layer 5. The second intermediate layer captures the leakage of dark current that occurs in the case of only the first intermediate layer, and can compensate for the lack of hole trapping capability. Thus, the electrical characteristics can be stabilized.

(Example 1-8, Comparative Example 1-2)
The radiographic image detector shown in FIG. 1 was produced as follows.
An electron blocking layer made of antimony sulfide (Sb ₂ S ₃ ) having a thickness of 2 μm was formed on a substrate on which switching TFTs and storage capacitors were arranged. Next, a Se raw material containing 3% of As was formed by vapor deposition to form a crystallization preventing layer having a layer thickness of 0.15 μm. Subsequently, a Se raw material containing 10 ppm of Na was deposited by vapor deposition to form a recording photoconductive layer made of amorphous Se having a layer thickness of 200 μm.

Subsequently, an a-Se layer containing LiF was formed as a second intermediate layer by co-evaporation. First, the Se raw material contained in the Ta boat was evaporated, and after the Se deposition rate was stabilized at 1 μm / min, evaporation of an appropriate amount of LiF raw material was started. The LiF raw material was put into an Al ₂ O ₃ crucible, and the crucible was heated with a tungsten filament (Example 1-8 and Comparative Example 2 were made by appropriately adjusting the input current to the tungsten filament) for a predetermined time. After co-evaporation, the vapor of the LiF boat and Se boat was simultaneously cut with a cell shutter to form a second intermediate layer having a thickness of about 1 to 30 μm (the thickness of the second intermediate layer was adjusted for the evaporation time) In Comparative Example 1, the second intermediate layer was not provided).

Subsequently, a first intermediate layer (hole blocking layer) made of antimony sulfide (Sb ₂ S ₃ ) having a layer thickness of 0.3 μm was formed on the _second intermediate layer. On the formed first intermediate layer, Au was deposited to form a bias electrode having a layer thickness of 0.1 μm. Finally, a voltage application cable was connected on the bias electrode, and a peripheral drive circuit was mounted on the TFT array X-ray charge conversion film substrate to complete the radiation image detector.

  It should be noted that a reference detector for measuring the following dark current and X-ray sensitivity by forming a similar film with the same configuration as above on a 5 cm square glass substrate provided with an amorphous IZO layer. It was.

(Measurement of image defects before and after accelerated test)
・ TFT pixel size: 150μm
・ Accelerated test: 40 ℃-3 months (Experiment was conducted at an accelerated test temperature of 40 ℃ and the accelerated test time was changed as appropriate, and the difference in increase in image defects could be identified over the course of 3 months of accelerated test. Therefore, this condition was used for evaluation.)
Application of electric field; measurement after 60 s after applying +2 kV to bias electrode Using the radiographic image detector produced above, the relative change in the number of image defects before and after the accelerated test under the above conditions was calculated. Regarding the number of image defects before and after the accelerated test, first, after applying +2 kV to the bias electrode, an offset image at 60 s is obtained, and abnormal density pixels exceeding 5 times the density fluctuation dispersion of this offset image are regarded as defective pixels. Considering this, the total number of abnormal pixels was calculated as the number of defective pixels. The number of defective pixels after the acceleration test is shown in Table 1 as a relative value with respect to Comparative Example 1.

(Measurement of dark current and X-ray sensitivity)
While applying +2 kV to the upper electrode of the reference detector, an ammeter was connected to the IZO layer to read out dark current and X-ray sensitivity. The dark current was measured as a current value for 60 s after applying the bias voltage. X-ray sensitivity is as follows. After applying a bias electric field for 600 s, X-rays (710 msec) through a tube voltage of 28 kV (Mo tube bulb), tube current of 80 mA, Mo filter of 30 μm, and Al filter of 2 mm are irradiated 10 times at 15 second intervals. Thereafter, a current value of 60 s was measured. Table 1 shows the dark current and X-ray sensitivity after repetition of each sample as relative values to Comparative Example 1.

(Measurement of the thickness of the second intermediate layer)
The thickness measurement of the second intermediate layer in the radiographic image detector is performed by measuring the concentration distribution of Li added to the Se film simultaneously formed on the Si substrate by using SIMS (secondary ion mass spectrometry). Then, the length was determined by measuring the length of the region sandwiched between the two most distant interfaces having a value of 10% of the maximum Li concentration in the intermediate layer. Using oxygen ions as primary ions used for SIMS analysis, the depth distribution measurement of Li was performed until Li reached the lower limit of detection. After completion of the SIMS measurement, the crater depth obtained by the measurement was directly measured using a stylus type surface level meter (P-10, manufactured by KLA-Tencor), and averaged as the value of the SIMS data end point. Table 2 shows the SIMS measurement conditions.

(Measurement of specific substance concentration in the second intermediate layer)
The LiF concentration in the intermediate layer was defined as the average Li concentration (mole) in the region sandwiched between the two most distant interfaces having a value of 10% of the maximum LiF concentration in the intermediate layer. Specifically, the total number of Li counts in the region sandwiched between the two interfaces is integrated, divided by the layer thickness of the second intermediate layer, and the average number of Li counts per unit layer thickness obtained is calculated as a sensitivity described later. According to the correction method, the Li concentration was converted to obtain an average Li concentration (mol). That is, the molar concentration of LiF is set to the LiF concentration with the concentration of Li, and the measured concentration value of F (halogen) may be lower than that of Li. The sensitivity correction method was performed as follows.

  Sensitivity correction method: Samples containing Se and LiF were prepared for sensitivity correction, and first, Se and Li concentrations were quantified by ICP-MS analysis. Next, the same sample was subjected to SIMS analysis, and a sensitivity correction coefficient was obtained so that the Se and Li concentrations coincided with the SIMS analysis value. Based on this sensitivity correction coefficient, the Li concentration distribution of a predetermined sample was quantified.

  Here, the LiF concentration was quantified as an average Li concentration (mol), but the concentration distribution of F (halogen) can be measured by SIMS in the same manner as Li. In this case, Cs ions are used as primary ions used for SIMS analysis. A plot of the specific substance concentration and the layer thickness measured in Examples 1 to 8 is shown in FIG.

  As is apparent from Table 1, in Examples 1 to 8 containing the LiF concentration of 0.0003 mol% or more and 0.003 mol% or less as the second intermediate layer, the increase in dark current after repeated X-ray irradiation was observed. It was significantly less than Comparative Examples 1-2.

  As is apparent from the above, the radiation image detector of the present invention is an a-Se layer containing LiF (alkali metal fluoride) between the first intermediate layer and the recording photoconductive layer. In addition, since the second intermediate layer having a specific substance concentration of 0.0003 mol% or more and 0.003 mol% or less is provided, an increase in dark current after repeated use is prevented, and image defects with time Increase, and a decrease in X-ray sensitivity can be prevented.

In this example, only LiF (alkali metal fluoride) was exemplified as the specific substance, but other alkali metal fluorides, alkali metal oxides, alkali metal earth fluorides, alkali metal earth oxides, SiO _x and GeO _x (both x are 0.5 ≦ x ≦ 1.5, preferably x = 1) can be used similarly. The above specific substances have a boiling point of about 1300 ° C. or less, the thermal damage to Se is almost the same, and are also about the same in that they form localized levels in a-Se that capture holes. . Moreover, it is considered that it exists in a molecular form in a-Se, and is difficult to diffuse in a-Se.

1 is a schematic cross-sectional view showing a configuration of a radiation image detector according to an embodiment of the present invention. Schematic sectional view showing the configuration of a radiation image detector according to another embodiment of the present invention Expanded cross section of active matrix layer Logarithmic graph showing the relationship between specific substance concentration and layer thickness in the second intermediate layer Schematic sectional view showing the configuration of the optical reading type radiation image detector of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Active matrix layer 3 Electron blocking layer 4 Anti-crystallization layer 5 Photoconductive layer for recording 6 Second intermediate layer 7 First intermediate layer 8 Bias electrode
10 Radiation image detector
11 Linear electrode
12 Photoconductive layer for reading
13 Power storage unit
31 TFT
32 Storage capacity

Claims (3)

A bias electrode that transmits a recording electromagnetic wave carrying image information; a recording photoconductive layer mainly composed of a-Se that generates a charge by irradiation of the recording electromagnetic wave that has passed through the bias electrode; In the radiation image detector formed by laminating the power storage unit for accumulating the generated charges, a plurality of reference electrodes, and a substrate in this order,
Of the bias electrode or the reference electrode, when reading the electric charge of the power storage unit, antimony sulfide is interposed between the electrode having a positive potential with respect to the power storage unit and the recording photoconductive layer. A first intermediate layer and specific substances such as alkali metal fluoride, alkaline earth metal fluoride, alkali metal oxide, alkaline earth metal oxide, SiO _x , GeO _x (where x is 0.5 ≦ x ≦ 1.5), and a second intermediate layer comprising an a-Se layer containing at least one kind is provided by laminating the second intermediate layer toward the recording photoconductive layer side,
The radiation image detector, wherein the second intermediate layer has a specific substance average concentration of 0.0003 mol% or more and 0.003 mol% or less.   When the average concentration of the specific substance in the second intermediate layer is x (mol%) and the layer thickness of the second intermediate layer is y (μm), x · y ≧ 0.0003 and y ≦ 30. The radiation image detector according to claim 1.   The radiation image detector according to claim 1, wherein the second intermediate layer has a thickness of 1 to 30 μm.

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