JPWO2012035583A1 - Radiation detector - Google Patents

Abstract

In the radiation detector of the present invention, the composition ratio of antimony in the second high resistance film containing antimony sulfide as a main component is set to 61 mol% or more and 80 mol%, which is higher than the conventional one. Also shows properties close to metals. Therefore, even if the resistance of the semiconductor layer is lowered when radiation is incident, the voltage applied to the second high resistance film can be made lower than that of the conventional example, so that the second high resistance film is prevented from being broken down. Can be suppressed. As a result, an increase in defective pixels can be suppressed even when the radiation detection operation is repeated, and durability can be improved.

Description

  The present invention relates to a radiation detector for measuring the spatial distribution of radiation in the medical field, industrial field, nuclear field, and the like.

  As a conventional example of a direct conversion type radiation detector that directly converts radiation into electric charge and accumulates electric charge, for example, a structure as shown in FIG. FIG. 11 is a longitudinal sectional view showing a schematic configuration of a radiation detector according to a conventional example.

  The conventional radiation detector includes, for example, an active matrix substrate 101, a semiconductor layer 103, an electrode layer 105, and a carrier collection electrode 107. The semiconductor layer 103 is made of a radiation sensitive semiconductor. The electrode layer 105 is formed on the surface of the semiconductor layer 103 and is used to apply a predetermined bias voltage. The carrier collecting electrode 107 is for collecting carriers generated in the semiconductor layer 103 when radiation enters the semiconductor layer 103. The active matrix substrate 101 takes out the charges collected by the carrier collection electrode 107 as a radiation detection signal at a predetermined timing. Note that when amorphous selenium (a-Se) is used for the semiconductor layer 103, a thick amorphous semiconductor can be easily formed over a wide region by a method such as vacuum evaporation. Therefore, amorphous selenium (a-Se) is suitable for constructing a two-dimensional array type radiation detector that requires a large-area thick film.

Since the radiation detector having the above-described configuration applies a high voltage to the electrode layer 105, dark current becomes a problem. In order to suppress this problem, some of them further include charge injection blocking layers 109 and 110. The charge injection blocking layer 109 is usually formed between the semiconductor layer 103 and the electrode layer 105, but there is a material whose composition ratio is devised in order to enhance the effect of the charge injection blocking layer 109. For example, the charge injection blocking layer 109 is made of an alloy of antimony sulfide (Sb _x S _y ), and the composition ratio of antimony (Sb) in the alloy is 41 mol% or more and 60 mol% or less (for example, Patent Document 1).

  Further, when the semiconductor layer 103 is made of amorphous selenium, there is a problem that interface crystallization proceeds at a contact portion between the electrode layer 105 and the semiconductor layer 103. Since charge injection increases as the interface crystallization progresses, an organic polymer layer 111 is provided as a suppression layer between the charge injection blocking layer 109 and the semiconductor layer 103 in order to suppress this. Since this organic polymer layer 111 may reduce the electron transport property, the component of the organic polymer layer 111 is devised. For example, there is one in which carbon clusters are added to the organic polymer layer 111 so that the ratio is 0.01 wt% to 50 wt% (see, for example, Patent Document 2).

Further, even when the charge injection blocking layer 109 and the organic polymer layer 111 are stacked between the electrode layer 105 and the semiconductor layer 103 as described above, the semiconductor layer 103 has a structure in which high voltage is applied. Creeping discharge may occur at the end face. In order to prevent this creeping discharge, the formation range of the organic polymer layer 111 is limited to only a portion having a film thickness of 10% or more of the average film thickness in the flat portion of the semiconductor layer 103 (for example, patents). Reference 3).
JP 2009-99933 A (paragraph numbers “0027” to “0038”, FIGS. 2 and 3) JP 2008-227347 A (paragraph numbers “0017” to “0025”, FIG. 2, paragraph numbers “0063” to “0065”, Table 1) JP 2009-99941 A (paragraph numbers “0084” to “0090”, FIG. 1)

  The conventional example can surely suppress the dark current, suppress the crystallization of the semiconductor layer 103, and further suppress the decrease in charge transport property due to the organic polymer layer 111. However, when X-ray imaging is repeatedly performed using the conventional radiation detector, there is a problem that the number of defective pixels increases and the quality of the X-ray detection image deteriorates.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a highly durable radiation detector that suppresses an increase in defective pixels even when a radiation detection operation is repeatedly performed. .

As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge.
In the conventional example, it was found that when a radiation is incident, a carrier current flows and the resistance of the semiconductor layer 103 decreases, so that a relatively high voltage is applied to the charge injection blocking layer 109. At this time, the applied voltage increases as the resistance value of the charge injection blocking layer 109 increases. However, in the conventional example, the main purpose is to suppress dark current, and the composition ratio of antimony (Sb) is reduced. Above, it is a high resistance layer. For this reason, when the radiation detection operation is repeated, the charge injection blocking layer 109 cannot withstand a high voltage, resulting in a location where the dark current increases due to breakdown. This portion appears as a defective pixel in the detected image, and the quality of the detected image decreases as the number of defective pixels increases.

  Further, when the charge injection blocking layer 109 and the organic polymer layer 111 are in a two-layer structure, the voltage applied to the charge injection blocking layer 109 is divided by the organic polymer layer 111 and the voltage applied to the charge injection blocking layer 109. The effect of lowering can be expected. However, the effect of this partial pressure depends on the concentration of carbon clusters added to the organic polymer layer 111. That is, if the concentration of carbon clusters is too low, the resistance of the organic polymer layer 111 becomes too high, so that the voltage applied to the organic polymer layer 111 becomes higher. Therefore, the organic polymer layer 111 reaches dielectric breakdown before the charge injection blocking layer 109. At that time, when the resistance of the charge injection blocking layer 109 is high, the voltage dividing effect disappears, and it has been found that even the charge injection blocking layer 109 reaches dielectric breakdown and a defective pixel is generated. If the concentration of the carbon cluster is too high, the resistance of the organic polymer layer 111 becomes too low, so that the partial pressure effect of the organic polymer layer 111 with the charge injection blocking layer 109 is reduced. Insulation breakdown cannot be suppressed. Therefore, it was also found that defective pixels occur as in the case where the concentration of carbon clusters is too low.

  The present invention based on such knowledge is configured as follows.

  That is, the radiation detector according to the present invention includes (a) a matrix substrate in which pixels for storing electric charges are two-dimensionally arranged and reading signals from the respective pixels; and (b) a first that selectively transmits carriers. A high-resistance film; (c) a semiconductor layer that generates carriers upon incidence of radiation; and (d) a carbon cluster or a carbon cluster for selectively transmitting carriers while being formed so as to cover the upper surface of the semiconductor layer. An organic polymer layer containing the derivative; (e) a second high-resistance film that is formed so as to cover the upper surfaces of the semiconductor layer and the organic polymer layer, and that selectively transmits carriers; f) an electrode layer for applying a bias voltage to the semiconductor layer via the second high resistance film, (g) the semiconductor layer, the first high resistance film, the organic polymer layer, And electrode layer In the radiation detector in which an insulating resin layer covering the entire exposed surface and (h) an insulating auxiliary plate surrounding the insulating resin layer are laminated in this order, the second high resistance film includes: The main component is antimony sulfide, and the average value of the antimony composition ratio is 61 mol% or more and 80 mol% or less.

  According to the radiation detector of the present invention, the composition ratio of antimony in the second high resistance film containing antimony sulfide as a main component is 61 mol% or more and 80 mol% higher than the conventional one. It shows properties closer to metals than the examples. Therefore, even if the resistance of the semiconductor layer is lowered when radiation is incident, the voltage applied to the second high resistance film can be made lower than that of the conventional example, so that the second high resistance film is prevented from being broken down. Can be suppressed. As a result, an increase in defective pixels can be suppressed even when the radiation detection operation is repeated, and durability can be improved.

  Note that the upper limit of the composition ratio of antimony is set to 80 mol%. The second high-resistance film is generally formed by vapor deposition, but even if a vapor deposition raw material having a high antimony concentration is used, 80 mol% is used. This is because it is technically very difficult to achieve a composition ratio exceeding 100%. In addition, if the antimony composition ratio is too high, it may be too close to the properties of the metal, and the function as the second high resistance film may be impaired.

  In the radiation detector of the present invention, it is preferable that the second high resistance film has an average antimony composition ratio of 67 mol% or more and 75 mol% or less.

  By setting the average value of the antimony composition ratio within this range, it is possible to effectively suppress the dielectric breakdown of the second high resistance film.

  In the radiation detector of the present invention, it is preferable that the organic polymer layer is configured so that the concentration of carbon clusters or derivatives thereof is 11 wt% or more and less than 30 wt%.

  If the concentration of the carbon cluster or derivative thereof in the organic polymer layer is within this range, the composition ratio is relatively low within the range of the composition ratio of the second high resistance film, and the second high resistance film has a high resistance. However, the voltage applied at the time of radiation incidence can be appropriately divided by the second high resistance film. Therefore, since the probability that the organic polymer layer and the second high resistance film are broken down is reduced, the occurrence of defective pixels can be suppressed. In addition, since an appropriate partial pressure effect by the organic polymer layer can be obtained, the second high resistance film can be made to have a relatively high resistance. Therefore, since the electric field can be prevented from concentrating on the thin portion of the semiconductor layer at the edge portion of the second high resistance film, the phenomenon that the semiconductor layer is broken by discharge can be suppressed.

  In the radiation detector of the present invention, it is preferable that the organic polymer layer has a concentration of carbon clusters or derivatives thereof of 15 wt% or more and 20 wt% or less.

  If the concentration of the carbon cluster or derivative thereof in the organic polymer layer is within this range, the composition ratio is relatively low within the range of the composition ratio of the second high resistance film, and the second high resistance film has a high resistance. However, the voltage applied at the time of radiation incidence can be more appropriately divided by the second high resistance film. Therefore, since the probability that the organic polymer layer and the second high resistance film are broken down further decreases, it is possible to further suppress the occurrence of defective pixels.

  A carbon cluster or a derivative thereof is an aggregate formed by bonding several to several hundred carbon atoms regardless of the type of carbon-carbon bond. However, it is not necessary to be composed only of 100% carbon clusters, and includes a mixture of other atoms and those having a substituent. Examples of the carbon cluster include fullerene C60, fullerene C70, and fullerene oxide. Fullerene is a general term for a carbon cluster of a spherical or rugby ball field composed of sp2 carbon.

  In the radiation detector of the present invention, the second high-resistance film has a formation region end outside the outer edge of the electrode layer, and an average film thickness of the semiconductor layer of 80% or more. The organic polymer layer is formed such that the end of the formation region is between the outer edge of the electrode layer and the outer edge of the second high resistance layer. It is preferable to be formed so as to be positioned.

  The second high resistance film and the organic polymer layer are formed so as to avoid a portion where the semiconductor layer is thin. Therefore, even when the resistance value of the second high resistance film or the organic polymer layer is relatively low, a portion where the film thickness of the semiconductor layer is thin at the edge of the second high resistance film or the organic polymer layer Since the electric field can be prevented from concentrating on the semiconductor layer, the phenomenon that the semiconductor layer is broken by discharge can be suppressed.

  According to the radiation detector of the present invention, the composition ratio of antimony in the second high resistance film containing antimony sulfide as a main component is set to 61 mol% or more and 80 mol%, which is higher than the conventional one. It shows properties that are closer to metals than conventional examples. Therefore, even if the resistance of the semiconductor layer is lowered when radiation is incident, the voltage applied to the second high resistance film can be made lower than that of the conventional example, so that the second high resistance film is prevented from being broken down. Can be suppressed. As a result, an increase in defective pixels can be suppressed even when the radiation detection operation is repeated, and durability can be improved.

It is a longitudinal cross-sectional view which shows schematic structure of the radiation detector which concerns on an Example. It is a figure which shows the connection relation of an active matrix substrate and an external circuit. It is a longitudinal cross-sectional view which shows the principal part of an active matrix substrate. It is a graph which shows the result of having quantified antimony composition ratio about detector 1 for a test. It is a graph which shows the mode of the increase of the defect pixel by X-ray irradiation about the detector 1 for a test. It is a graph which shows the result of having quantified antimony composition ratio about detector 2 for a test. It is a graph which shows the mode of the increase of the defect pixel by X-ray irradiation about the detector 2 for a test. 6 is a photograph showing the state of occurrence of defective pixels in the test detector 2; It is a graph which shows the result of having quantified antimony composition ratio about the detector for a comparison. It is a graph which shows the mode of the increase in the defect pixel by X-ray irradiation about the detector for a comparison. It is a longitudinal cross-sectional view which shows schematic structure of the radiation detector which concerns on a prior art example.

DESCRIPTION OF SYMBOLS 1 ... Active matrix substrate 3 ... 1st high resistance film 5 ... Semiconductor layer 7 ... Organic polymer layer 9 ... 2nd high resistance film 11 ... Electrode layer 13 ... Spacer 15 ... Auxiliary plate 17 ... Insulating resin layer DU ... Detection element

  An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of a radiation detector according to an embodiment.

  The radiation detector includes an active matrix substrate 1, a first high resistance film 3, a semiconductor layer 5, an organic polymer layer 7, a second high resistance film 9, an electrode layer 11, a spacer 13, An auxiliary plate 15 and an insulating resin layer 17 are provided.

  Although described in detail later, the active matrix substrate 1 has a function of reading out charges associated with the incidence of radiation. The first high-resistance film 3 has a function of selectively transmitting carriers, and is formed on the active matrix substrate 1 with an antimony sulfide alloy. The film formation is performed by, for example, vacuum deposition and has a thickness of about 2 μm. The semiconductor layer 5 generates carriers by the incidence of radiation, and is formed on the upper surface of the first high resistance film 3 by, for example, amorphous selenium (a-Se). The semiconductor layer 5 is formed by, for example, vacuum vapor deposition, and has a thickness of about 1 mm at the thickest portion.

  The organic polymer layer 7 has a function of suppressing interface crystallization of the semiconductor layer 5 and a function of selectively transmitting carriers, and is formed on the upper surface of the semiconductor layer 5. The organic polymer layer 7 is formed by, for example, applying a thickness of about 0.2 μm by an inkjet method and then drying. The organic polymer layer 7 includes, for example, an organic polymer such as acrylic organic resin, polyimide, BCB, PVA, acrylic, polyethylene, polycarbonate, and polyetherimide. Further, the organic polymer layer 7 includes carbon clusters and derivatives thereof. A carbon cluster or a derivative thereof is an aggregate formed by bonding several to several hundred carbon atoms regardless of the type of carbon-carbon bond. The carbon cluster does not need to be composed of only 100% carbon cluster, and may contain a mixture of other atoms or a substituent. The carbon cluster includes, for example, one or several fullerenes. In addition, fullerene is a general term for spherical or rugby ball-like carbon clusters made of sp2 carbon. Generally, C60, C70, C76, C78, C84 etc. are mentioned. The concentration of carbon clusters or derivatives thereof contained in the organic polymer layer 7 is preferably within a predetermined range described later.

  The second high resistance film 9 has a function of selectively transmitting carriers, and is attached so as to cover the upper surface of the organic polymer layer 7. The second high resistance film 9 is formed in the same manner as the first high resistance film 3 described above, and has a thickness of about 1 μm, for example. The second high resistance film 9 is made of an antimony sulfide alloy, like the first high resistance film 3. However, the composition ratio is preferably within a predetermined range described later.

  A bias voltage is applied to the electrode layer 11 from a bias voltage supply unit (not shown). The electrode layer 11 is made of, for example, gold (Au). The formation is performed, for example, by vacuum deposition, and is formed to a thickness of about 0.1 μm.

  The spacer 13 is erected in the vicinity of the outer edge of the active matrix substrate 1 and forms a space for protecting various films and layers stacked on the active matrix substrate 1 described above. The auxiliary plate 15 closes the space surrounded by the spacers 13. The auxiliary plate 15 preferably has a thermal expansion coefficient comparable to that of the active matrix substrate 1 and a high radiation transmittance. Specific examples of the auxiliary plate 15 include borosilicate glass and quartz glass. The insulating resin layer 17 is injected so as to fill a space formed by the spacer 13, the auxiliary plate 15, and the active matrix substrate 1. As a material for the insulating resin layer 17, a material having high insulation, high hardness, and good adhesiveness is suitable, and examples thereof include an epoxy resin.

  The second high-resistance film 9 described above is preferably formed so that the outer edge is located outside the outer edge of the electrode layer 11. Further, it is preferable that the position is satisfied and the following relationship with the film thickness of the semiconductor layer 5 is satisfied. That is, the second high resistance film 9 is formed in the region of the semiconductor layer 5 having a thickness of 80% or more of the average thickness of the semiconductor layer 5. For example, as shown in FIG. 1, the second high resistance film 9 is formed only in the region Rg including the central portion from the shoulder portion of the semiconductor layer 5.

  The organic polymer layer 7 is preferably formed so that the outer edge is located between the outer edge of the electrode layer 11 and the outer edge of the second high resistance film 9.

  When these formation conditions (hereinafter referred to as “inherent formation conditions”) are satisfied, the second high resistance film 9 and the organic polymer layer 7 are formed so as to avoid the portion where the semiconductor layer 5 is thin. Will be. Therefore, even when the resistance value of the second high resistance film 9 or the organic polymer layer 7 is relatively low, the edge of the second high resistance film 9 or the organic polymer layer 7 is not affected Since it is possible to suppress the concentration of the electric field in the portion where the film thickness is thin, it is possible to suppress the phenomenon that the semiconductor layer 5 is damaged by discharge.

  Reference is now made to FIGS. 2 is a diagram showing a connection relationship between the active matrix substrate and an external circuit, and FIG. 3 is a longitudinal sectional view showing a main part of the active matrix substrate. In FIG. 3, the first high resistance film 3, the organic polymer layer 7, and the second high resistance film 9 are not shown for convenience of explanation.

  The active matrix substrate 1 has detection elements DU arranged in a two-dimensional matrix and is patterned on an insulating substrate 21 such as glass. The active matrix substrate 1 includes a carrier collection electrode 23, a capacitor Ca, and a thin film transistor Tr. The carrier collection electrode 23 collects the charge signal converted by the semiconductor layer 5. The capacitor Ca accumulates the charge signal collected by the carrier collection electrode 23. The thin film transistor Tr is a switching element that is turned on and off by an external signal and reads a charge signal accumulated in the capacitor Ca. One detection element DU corresponding to the “pixel” in the present invention is composed of a set of a carrier collection electrode 23, a capacitor Ca, a thin film transistor Tr, and a semiconductor layer 5 and an electrode layer 11 in a region corresponding to these. Yes. A bias voltage Va is applied to the electrode layer 11. Here, in order to facilitate understanding of the description, it is assumed that the two-dimensional matrix of the active matrix substrate 1 is composed of 10 × 10 detection elements DU for convenience.

  The active matrix substrate 1 includes gate lines G1 to G10 and data lines D1 to D10. The gate lines G1 to G10 are electrically connected to the gate of the thin film transistor Tr for each row of the detection elements DU. The data lines D1 to D10 are electrically connected to the reading side of the thin film transistor Tr for each column of the detection elements DU. In the following description, the gate lines G1 to G10 and the data lines D1 to D10 are referred to as the gate line G and the data line D unless particularly distinguished.

  A gate drive circuit 25 is connected to the gate lines G1 to G10. In addition, a charge-voltage conversion amplifier 27, a multiplexer 29, and an A / D converter 31 are connected to the data lines D1 to D10 in that order.

  The gate drive circuit 25 applies a voltage to the gate line G to turn on the thin film transistor Tr and output the charge signal stored in the capacitor Ca from the data line D to the charge voltage conversion amplifier 27. The charge-voltage conversion amplifier 27 converts the received charge signal into a voltage signal. The multiplexer 29 outputs a plurality of voltage signals as one voltage signal. The A / D converter 31 converts the voltage signal from the multiplexer 29 into a digital signal. Although not shown, a processing unit is connected to the subsequent stage of the A / D converter 31 and generates a fluoroscopic image based on a plurality of voltage signals.

  Next, two types of test samples prepared for the radiation detector having the above-described configuration will be described.

<Test detector 1>
Reference is now made to FIGS. FIG. 4 is a graph showing the result of quantifying the antimony composition ratio for the test detector 1, and FIG. 5 is a graph showing an increase in the number of defective pixels due to X-ray irradiation for the test detector 1. .

The test detector 1 uses an antimony sulfide raw material having an antimony composition ratio of 45 mol% and forms a second high resistance film 9 by vacuum deposition. FIG. 4 shows the result of measuring the X-ray photoelectron spectroscopy spectrum using X-ray photoelectron spectroscopy and quantifying the constituent elements of the second high resistance film 9 in the test detector 1. . Here, the SiO ₂ equivalent sputter depth (SiO ₂ equivalent depth) on the horizontal axis represents the depth from the surface, and 200 nm in the figure corresponds to about 1 μm in terms of the film thickness of Sb _x S _y . Atomic Concentration on the vertical axis indicates the concentration of the constituent elements. In the legend, for example, the parenthesis of Sb (Sb ₃ d ₅ ) represents the electron orbit of antimony Sb. From this quantitative result, it can be seen that the composition ratio of antimony Sb in the antimony sulfide Sb _x S _y in the second high resistance film 9 of the test detector 1 is in the range of 67% to 75%. Carbon C is detected in the vicinity of the surface of the second high resistance film 9 whose depth is near zero. This is included in a natural oxide film or the like generated on the surface of the second high resistance film 9. Therefore, the location where the carbon C rapidly decreases indicates the substantial surface of the second high resistance film 9. Further, indium In increases from around 200 nm. This is because the second high resistance film 9 for composition analysis is formed on a glass substrate on which an ITO (Indium Tin Oxide) electrode is formed, and before the increase, the second high resistance film 9 is formed. 9 is shown.

  Further, the organic polymer layer 7 of the test detector 1 was prepared by a coating solution in which 2.5 wt% polycarbonate resin and fullerene C60 were dissolved in o-dichlorobenzene as an organic compound. In order to estimate the optimum fullerene C60 concentration, solutions having fullerene C60 concentrations of 15 wt%, 30 wt%, and 45 wt% with respect to the polycarbonate resin were prepared and applied onto the semiconductor layer 5 separately. Specifically, a solution having fullerene C60 concentrations of 15 wt%, 30 wt%, and 45 wt% was applied on one semiconductor layer 5 in a strip shape. In addition, the semiconductor layer 5 is planar, and it is applied repeatedly so that there is no overlap in the plane with a set of three application band regions so that there is no significant difference due to the application location. did.

  This test detector 1 was irradiated with intense X-rays to measure how the defective pixels increased. The X-ray irradiation conditions were a distance of 1.3 m, a tube voltage of 120 kV, and a tube current of 360 mA. Then, X-rays under that condition were irradiated every 30 seconds for 0.1 second. The dose of one irradiation is 2.17 mGy (milli gray), which corresponds to the dose used for one year in an average medical chest X-ray diagnostic apparatus at about 5,000 times. As shown in FIG. 5, in the test detector 1, in any region where the fullerene C60 concentration was 15 wt% to 45 wt%, the number of missing pixels was 10 or less even when 30,000 times of X-ray irradiation was performed. .

<Test detector 2>
Reference is now made to FIGS. FIG. 6 is a graph showing the result of quantifying the antimony composition ratio for the test detector 2, and FIG. 7 is a graph showing an increase in defective pixels due to X-ray irradiation for the test detector 2.

The test detector 2 uses an antimony sulfide raw material having an antimony composition ratio of 44 mol% and forms a second high resistance film 9 by vacuum deposition. FIG. 6 shows quantitative results using X-ray photoelectron spectroscopy, and the second high resistance film 9 of the test detector 2 has an antimony Sb composition ratio of 61% to 69 in antimony sulfide Sb _x S _y . It can be seen that it is in the range of%.

  For the organic polymer layer 7, solutions having fullerene C60 concentrations of 10 wt%, 15 wt%, 20 wt%, and 30 wt% with respect to the polycarbonate resin were prepared and applied onto the semiconductor layer 5 separately. Specifically, a solution having fullerene C60 concentrations of 10 wt%, 15 wt%, 20 wt%, and 30 wt% was applied on one semiconductor layer 5 in a strip shape. In addition, the semiconductor layer 5 is planar and is applied repeatedly so as not to overlap in the plane with a set of application band regions at four different concentrations so that no significant difference occurs due to the application location. did. Note that the number of pixels in the active matrix substrate 1 is 2880 × 2880, and 120 × 2880 in the above one coating zone.

  The state in which the number of defective pixels of the test detector 2 increases was measured under the same conditions as the irradiation conditions described above. The result is shown in FIG. In the test detector 2, in the regions where the fullerene C60 concentrations were 10 wt% and 30 wt%, the number of defective pixels was 100 or less after 20,000 irradiations. In the regions where the fullerene C60 concentrations were 15 wt% and 20 wt%, the number of defective pixels was 100 or less after 30,000 irradiations.

  Reference is now made to FIG. FIG. 8 is a photograph showing the state of occurrence of defective pixels in the test detector 2.

  This photograph shows the state of occurrence of defective pixels after the test detector 2 is irradiated with X-rays 37,500 times under the above-described irradiation conditions. The upper part and the lower part of the photograph show two different areas in the test detector 2, and the white dots in the photograph indicate defective pixels. As is apparent from this photograph, it can be seen that a large number of defective pixels are generated in regions where the fullerene C60 concentrations are 10 wt% and 30 wt%.

  Based on the above results, if the antimony sulfide antimony composition ratio in the second high resistance film 9 is 67 mol% or more and 75 mol% or less, the fullerene C60 concentration in the organic polymer layer 7 is in a wide range of 10 wt% to 45 wt%. It has been found that the increase in defective pixels can be suppressed even when X-ray irradiation is repeated. Even if the antimony composition ratio of antimony sulfide in the second high resistance film 9 is relatively low from 61 mol% to 69 mol%, the fullerene C60 concentration in the organic polymer layer 7 is 15 wt% to less than 30 wt%, preferably 15 wt%. It was found that if the amount was limited to 20% by weight, the increase in defective pixels could be suppressed.

  The upper limit of the antimony composition ratio of antimony sulfide was 80 wt%. This is because the second high-resistance film 9 is generally produced by vapor deposition, but the antimony composition ratio in the second high-resistance film 9 is 80 mol even if the vapor deposition raw material having a high antimony concentration is used. It is because it is very difficult technically to make it more than%. On the other hand, if the antimony composition ratio is too high, the properties of the second high-resistance film 9 are deteriorated because the properties of the second high-resistance film 9 are too low, and the thin portion of the semiconductor layer 5 is formed at the edge of the second high-resistance film 9. It also depends on the concentration of the electric field and the breakdown of the semiconductor layer 5.

  Further, even when the antimony composition ratio of antimony sulfide is 61 wt% to 80 wt% or less, there is a possibility that the resistance decreases and the potential increases at the edge portion of the second high resistance film 9. However, if the specific formation conditions of the second high-resistance film 9 and the organic polymer layer 7 described above are satisfied, the electric field can be prevented from concentrating on a thin portion of the semiconductor layer 5 even if the potential is increased. The discharge breakdown of the semiconductor layer 5 can be suppressed.

<Comparative detector>
Reference is now made to FIGS. FIG. 9 is a graph showing the result of quantifying the antimony composition ratio for the comparative detector, and FIG. 10 is a graph showing how the number of defective pixels increases due to X-ray irradiation for the comparative detector.

The comparative detector uses an antimony sulfide raw material having an antimony composition ratio of 40 wt% and forms the second high resistance film 9 by vacuum deposition. FIG. 9 shows the result of quantification using X-ray photoelectron spectroscopy. From now on, the second high resistance film 9 of the comparative detector has a composition ratio of antimony Sb in antimony sulfide Sb _x S _y of 56% to 60%. It turns out that it exists in the range. This corresponds to the composition ratio of the conventional example.

  For the organic polymer layer 7 in the detector for comparison, solutions having fullerene C60 concentrations of 10 wt%, 15 wt%, 30 wt%, and 40 wt% with respect to the polycarbonate resin were prepared and applied onto the semiconductor layer 5 separately.

  The state in which the number of defective pixels of the comparative detector increased was measured under the same conditions as the irradiation conditions described above. The result is shown in FIG. In the comparative detector, in all the regions where the fullerene C60 concentration was 10 wt% to 40 wt%, the number of defective pixels exceeded 100 by 10,000 irradiations. In particular, in the region where the fullerene C60 concentration was 40 wt%, the number of defective pixels exceeded 1,000 by 5,000 times of irradiation.

  The comparison detector is clearly different from the above-described test detectors 1 and 2 according to the present invention, and repeated X-ray imaging increases the number of defective pixels and degrades the quality of the X-ray detection image. It turns out that the phenomenon of going is remarkable.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, the semiconductor layer 5 is simply amorphous selenium (a-Se). For example, an amorphous body of selenium compound, an amorphous body of Se or Se compound doped with As or Te, an alkali metal The semiconductor layer 5 may be made of an amorphous body of Se doped with or an Se compound doped with alkali metal.

  (2) In the above-described embodiment, the second high resistance film 9 and the organic polymer layer 7 satisfy the inherent formation conditions. However, if the problem does not occur due to the concentration of the electric field at the edge portion of the second high resistance film 9 or the organic polymer layer 7 where the film thickness of the semiconductor layer 5 is thin, this unique formation condition is satisfied. There is no need.

  (3) In the embodiment described above, the active matrix substrate 1 is employed as the matrix substrate, but a passive matrix substrate may be provided instead.

  As described above, the present invention is suitable for a radiation detector for measuring the spatial distribution of radiation.

Claims (5)

(A) a matrix substrate in which pixels for accumulating charges are two-dimensionally arranged and reads a signal from each pixel;
(B) a first high-resistance film that selectively transmits carriers;
(C) a semiconductor layer that generates carriers upon incidence of radiation;
(D) an organic polymer layer formed so as to cover the upper surface of the semiconductor layer and containing carbon clusters or derivatives thereof to selectively transmit carriers;
(E) a second high-resistance film that is formed so as to cover the upper surfaces of the semiconductor layer and the organic polymer layer, and that selectively transmits carriers;
(F) an electrode layer for applying a bias voltage to the semiconductor layer via the second high-resistance film;
(G) an insulating resin layer covering the entire exposed surface of the semiconductor layer, the first high-resistance film, the organic polymer layer, and the electrode layer;
(H) an insulating auxiliary plate surrounding the insulating resin layer;
In the radiation detector in which are stacked in this order,
The second high resistance layer is composed of antimony sulfide as a main component, and the antimony composition ratio has an average value of 61 mol% or more and 80 mol% or less. The radiation detector according to claim 1.
The second high resistance film is configured to have an average antimony composition ratio of 67 mol% or more and 75 mol% or less. The radiation detector according to claim 1 or 2,
The radiation detector according to claim 1, wherein the organic polymer layer has a carbon cluster or a derivative concentration of 11 wt% or more and less than 30 wt%. The radiation detector according to claim 1 or 2,
The radiation detector according to claim 1, wherein the organic polymer layer has a carbon cluster or a derivative concentration of 15 wt% or more and 20 wt% or less. The radiation detector according to any one of claims 1 to 4,
The second high-resistance film is located on the region where the end of the formation region is outside the outer edge of the electrode layer and the average thickness of the semiconductor layer is 80% or more. Formed, and
The organic polymer layer is formed such that an end of a region where the organic polymer layer is formed is located between an outer edge of the electrode layer and an outer edge of the second high resistance layer.

Images