JP2005268452A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector improved in the sensitivity of an X-ray photoconductive film. <P>SOLUTION: A lead excess layer 25 and an iodine excess layer 23 are formed on and beneath an X-ray photoconductive film 5, respectively. The X-ray photoconductive film 5 pinched by the lead excess layer 25 and the iodine excess layer 23 becomes in pn junction. Thus, a conduction type in the X-ray photoconductive film 5 can be easily controlled. The generation of dark current can be reduced that degrades the quality of an X-ray image signal in an X-ray detector 1. Then, the sensitivity of the X-ray photoconductive film 5 is improved, and an unnecessary new synthetic element is removed. The X-ray detector 1 is made higher in performance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a radiation detector including a pixel electrode and a radiation photoconductive layer.

  As a new generation X-ray diagnostic image detector, an active matrix type flat panel detector has attracted much attention. By detecting irradiated X-rays in this flat detector, an X-ray image or a real-time X-ray image is output as a digital signal. In addition, since this flat detector is a solid state detector, it is highly expected in terms of image quality performance and stability.

  As the first application for practical use, it has been developed for the chest or general radiography for collecting still images with a relatively large dose, and has been commercialized in recent years. Commercialization is expected in the near future for applications in the circulatory and gastrointestinal fields that need to achieve higher performance and real-time video with more than one frame per second under fluoroscopic dose. For this moving image application, improvement of S / N and real-time processing technology of minute signals are important development items.

  And this type of flat detector is roughly divided into two types, a direct method and an indirect method. In the direct method, incident X-rays are obtained by a-Se or the like, and the photoconductive charge generated inside the body inside the X-ray photoconductive layer is directly converted into a charge signal by a high electric field, and the converted signal charge is used for charge accumulation. This is a method of storing in a capacitor.

  Further, the direct X-ray detector includes a TFT circuit substrate in which a charge storage capacitor, a switching element, a photodiode, and a pixel electrode are provided for each pixel arranged in a matrix on a holding substrate. A configuration in which an X-ray photoconductive layer is laminated on this TFT circuit substrate is known (see, for example, Patent Document 1).

  In the direct X-ray detector, an X-ray photoconductive material is used as the X-ray photoconductive layer in order to convert incident X-rays into a charge signal. When this X-ray photoconductive material is applied to a medical X-ray detector, the X-ray photoconductive material is required to have a size that can sufficiently cover the human body, for example, a size of about 40 cm on a side. The X-ray photoconductive material is usually formed as a film having a uniform thickness on a TFT circuit substrate provided with an electric circuit for accumulating signal charges and reading out the signal charges. In addition, in order to sufficiently detect incident X-rays, a thickness of several hundred μm is required even when a material made of heavy metal and having a large specific gravity is used.

  This X-ray photoconductive material is a kind of semiconductor, and its characteristics may change greatly depending on the crystal structure and composition. Generally, the best characteristics are obtained in a single crystal state. However, a semiconductor single crystal material having a sufficient size required for an X-ray detector has not been obtained.

In the direct method, the TFT circuit substrate constituting the X-ray detector is manufactured by a method similar to the manufacturing process of the liquid crystal display device. For example, a pixel electrode is formed on the surface of the holding substrate, and an X-ray photoconductor layer is formed on the holding substrate including the pixel electrode. In order to selectively input the output of the X-ray photoconductor layer to each pixel electrode, in many cases, for example, an insulating film of silicon oxide (SiO ₂ ) is provided so as to surround the pixel electrode. Yes. Further, aluminum, ITO, or the like is used for the pixel electrode.

Further, the X-ray photoconductive layer has a material for efficiently converting X-rays into a charge signal, such as lead iodide (PbI ₂ ), mercury (HgI ₂ ), bismuth iodide (BiI ₃ ), indium iodide ( InI) is used. Accordingly, aluminum or ITO used for the pixel electrode and lead iodide, mercury iodide, bismuth iodide, or indium iodide used for the X-ray photoconductive layer are in direct contact with each other.

In the direct X-ray detector, an X-ray photoconductive layer using lead iodide, mercury iodide, bismuth iodide, or indium iodide is formed on the pixel electrode by, for example, vacuum evaporation. The film is formed to a thickness of several hundred μm. In addition, a bias electrode layer for supplying charges is formed on the X-ray photoconductive layer.
Japanese Patent Laid-Open No. 10-10237 (page 4-6, FIGS. 1 and 2)

  As described above, in the direct X-ray detector, the X-ray photoconductive layer is formed on the TFT circuit substrate manufactured using the manufacturing process of the liquid crystal display device. This X-ray photoconductive layer is a kind of semiconductor, but unlike ordinary semiconductors such as silicon and gallium arsenide, the X-ray photoconductive layer is made of heavy metal to absorb X-rays efficiently. These iodides are mainly used to produce Typically, a substance such as lead iodide or mercury iodide is used as the main component of the X-ray photoconductive layer. These X-ray photoconductive layers are different from ordinary semiconductors in that it is not easy to control the conductivity type to bring out P-type or N-type properties.

  In particular, when a weak signal such as an X-ray detector is required to be detected with high precision, it is important to improve the sensitivity of the X-ray photoconductive layer and suppress unnecessary signal components. In order to realize this problem, there is a problem that it is necessary to form a junction state between the P-type and the N-type in the X-ray photoconductive layer by controlling the conductivity type.

  This invention is made | formed in view of such a point, and it aims at providing the radiation detector which can improve the sensitivity of a radiation photoconductive layer.

  The present invention relates to a circuit board provided with a pixel electrode, a radiation photoconductive layer which is provided on the pixel electrode of the circuit board and converts incident radiation into an electrical signal and contains metal iodide, and the radiation photoconductive layer An electrode layer provided on the pixel electrode so as to face the pixel electrode, and an iodine thin film layer provided between the radiation photoconductive layer and any one of the electrode layer and the pixel electrode.

  A radiation photoconductive layer that converts incident radiation into an electrical signal and contains a metal iodide is provided on the plurality of pixel electrodes of the circuit board, and the electrodes are opposed to the plurality of pixel electrodes on the radiation photoconductive layer. Provide a layer. An iodine thin film layer is provided between the radiation photoconductive layer and any of the electrode layer and the plurality of pixel electrodes. As a result, since the conductivity type in the radiation photoconductive layer is easily controlled by the iodine thin film layer, the generation of dark current in the radiation photoconductive layer can be reduced, and thus the sensitivity of the radiation photoconductive layer can be improved. .

  According to the present invention, a radiation photoconductive layer containing metal iodide provided on a plurality of pixel electrodes of a circuit board, and an electrode layer and a plurality of electrodes provided on the radiation photoconductive layer so as to face the plurality of pixel electrodes. By providing an iodine thin film layer with any one of the pixel electrodes, control of the conductivity type in the radiation photoconductive layer is facilitated by the iodine thin film layer. Therefore, generation of dark current in the radiation photoconductive layer is prevented. Since it can reduce, the sensitivity of this radiation photoconductive layer can be improved.

  Hereinafter, the configuration of the first embodiment of the radiation detector of the present invention will be described with reference to FIGS.

  1 to 3, reference numeral 1 denotes an X-ray detector as a radiation detector. The X-ray detector 1 is a direct X-ray planar image detector. As shown in FIG. 2, the X-ray detector 1 includes a TFT circuit substrate 3 as a photoelectric conversion substrate having a plurality of pixels 2 arranged in a matrix.

  An X-ray photoconductor layer 4 as a radiation photoconductor layer that converts incident radiation into an electrical signal is laminated and provided on the surface that is one main surface of the TFT circuit substrate 3. The X-ray photoconductor layer 4 is in a pn junction state and is in contact with the surface of the TFT circuit substrate 3. Therefore, the X-ray photoconductor layer 4 is directly formed on the TFT circuit substrate 3.

Here, the X-ray photoconductor layer 4 includes an X-ray photoconductive film 5 as a radiation photoconductive layer. The X-ray photoconductive film 5 is formed by vacuum-depositing an X-ray photoconductive material, such as lead iodide (PbI ₂ ), which is a heavy metal and has semiconducting properties, on the TFT circuit substrate 3 to a thickness of about 300 μm. ing. Further, a bias electrode layer 6 as an upper electrode is provided on the surface which is one main surface of the X-ray photoconductive film 5.

  As shown in FIG. 3, the TFT circuit substrate 3 includes a holding substrate 11 as an insulating substrate formed of a rectangular flat plate-shaped glass having translucency. A TFT circuit layer 12 and a pixel electrode 13 are formed for each pixel 2 on the surface which is one main surface of the holding substrate 11. The pixel electrode 13 is disposed so as to cover most of the outermost surface of the TFT circuit substrate 3.

  Further, the TFT circuit layer 12 includes a thin film transistor (TFT) 14 as a switching element and a charge storage capacitor 15 as a capacitor. Each of the pixel electrode 13, the thin film transistor 14, and the charge storage capacitor 15 is formed for each pixel 2 on the holding substrate 11. That is, each of the pixel electrode 13, the thin film transistor 14 and the charge storage capacitor 15 has a grid-like arrangement in which these are one set, and each set corresponds to the pixel 2 of the X-ray image. Has been.

  On the holding substrate 11, control electrodes 16 are wired as a plurality of control lines along the row direction of the holding substrate 11. The plurality of control electrodes 16 are located between the respective pixels 2 on the holding substrate 11 and are separated from each other in the column direction of the holding substrate 11. These control electrodes 16 are electrically connected to the gate electrode 17 of the thin film transistor 14.

  Furthermore, a plurality of readout electrodes 18 are wired on the holding substrate 11 along the column direction of the holding substrate 11. The plurality of readout electrodes 18 are located between the respective pixels 2 on the holding substrate 11 and are separated from each other in the row direction of the holding substrate 11. A source electrode 19 of the thin film transistor 14 is electrically connected to the plurality of readout electrodes 18. The drain electrode 20 of the thin film transistor 14 is electrically connected to the charge storage capacitor 15 and the pixel electrode 13, respectively.

  On the other hand, as shown in FIG. 1, on the TFT circuit layer 12 on the holding substrate 11, island-like pixel electrodes 13 are stacked in a matrix so as to correspond to the respective pixels 2. An iodine thin film layer 22 as a first thin film layer is laminated on the entire surface of the TFT circuit layer 12 including the pixel electrode 13. The iodine thin film layer 22 contains iodine as a main component. Further, the iodine thin film layer 22 is provided at the interface between the X-ray photoconductive film 5 and the TFT circuit substrate 3 in order to realize a PN junction state inside the X-ray photoconductive film 5.

  Further, on the lower side surface of the X-ray photoconductive film 5 in contact with the iodine thin film layer 22, the iodine component contained in the iodine thin film layer 22 is exposed to the inside of the X-ray photoconductive film 5 by an operation such as heat treatment. An iodine excess layer 23 formed by micro-diffusion is provided. The iodine excess layer 23 is a P-type semiconductor layer containing excess iodine. The iodine excess layer 23 is provided under the X-ray photoconductive film 5 between the iodine thin film layer 22 and the X-ray photoconductive film 5.

  An X-ray photoconductive film 5 is laminated on the iodine thin film layer 22, and a metal element thin film layer as a second thin film layer mainly composed of lead is formed on the entire surface of the X-ray photoconductive film 5. A certain lead thin film layer 24 is laminated. The lead thin film layer 24 is provided at the interface between the X-ray photoconductive film 5 and the bias electrode layer 6 in order to realize a PN junction state inside the X-ray photoconductive film 5.

  Furthermore, on the upper side surface of the X-ray photoconductive film 5 in contact with the lead thin film layer 24, the lead component contained in the lead thin film layer 24 is exposed to the inside of the X-ray photoconductive film 5 by an operation such as heat treatment. A lead-excess layer 25 formed by micro-diffusion is provided. This lead-excess layer 25 is an n-type semiconductor layer containing excessive lead. The lead excess layer 25 is provided in an upper layer of the X-ray photoconductive film 5 between the lead thin film layer 24 and the X-ray photoconductive film 5. Here, each of the lead excess layer 25 and the iodine excess layer 23 is such that the ratio of the lead content in the lead excess layer 25 and the iodine content in the iodine excess layer 23 is exactly 1: 2. It is configured.

  A bias electrode layer 6 is laminated on the entire surface of the lead thin film layer 24. The bias electrode layer 6 is provided to face each pixel electrode 13 and is formed flush with the entire surface of the lead thin film layer 24.

  Next, the operation of the X-ray detector of the first embodiment will be described.

  First, when X-rays are incident on the X-ray photoconductive film 5 of the X-ray detector 1 from the outside, the incident X-rays L that have entered the X-ray photoconductive film 5 It is absorbed by and excited.

  A large number of pairs of electrons e and holes h are generated inside the X-ray photoconductive film 5 by the energy of the incident X-ray L itself.

  At this time, a voltage of several hundred volts is applied between the bias electrode layer 6 and the pixel electrode 13 to form a bias electric field, so that the photoconductive charge Q generated in the X-ray photoconductor film 5 becomes a bias electric field. Move by.

  Then, either the electron e or the hole h moves to the pixel electrode 13 as the photoconductive charge Q and reaches.

  Thereafter, the photoconductive charge Q that has flowed into and flowed into the respective pixel electrodes 13 flows into the respective pixels until the gate electrode 17 of the thin film transistor 14 connected to the respective pixel electrodes 13 is driven, that is, turned on. It moves to the charge storage capacitor 15 connected to the electrode 13 and is held and stored.

  At this time, when one of the control electrodes 16 is in a drive state, the horizontal row of thin film transistors 14 connected to the control electrode 16 in the drive state is turned on.

  Then, the photoconductive charge Q stored in the charge storage capacitor 15 connected to each thin film transistor 14 in the on state is output to the readout electrode 18.

  As a result, a signal corresponding to a pixel in a specific row of the X-ray image is output. Therefore, by controlling the driving of the control electrode 16 to be turned on in order, it corresponds to all the pixels of the X-ray image. A signal can be output, and by converting this output signal into a digital image signal, it can be output to the outside as an X-ray image.

  Next, the X-ray detector manufacturing apparatus according to the first embodiment will be described.

  In FIG. 4, reference numeral 31 denotes a vacuum vapor deposition apparatus 31 as an apparatus for manufacturing an X-ray detector. The vacuum vapor deposition apparatus 31 includes a chamber 32 in which the TFT circuit board 3 is installed. The chamber 32 makes the atmosphere in the chamber 32 an atmosphere different from the outside, that is, a vacuum. A vacuum pump 33 is attached to the chamber 32 to evacuate the chamber 32. The vacuum pump 33 evacuates the inside of the chamber 32.

  Further, a substrate heating device 34 facing the back surface of the TFT circuit substrate 3 installed inside the chamber 32 is attached inside the chamber 32. The substrate heating device 34 heats the TFT circuit substrate 3 installed in the chamber 32 to a predetermined temperature. In the chamber 32, an iodine evaporation source 35, a lead iodide evaporation source 36, and a lead evaporation source 37, which are installed to face the substrate heating device 34, are installed. Each of the iodine evaporation source 35, the lead iodide evaporation source 36 and the lead evaporation source 37 is configured to face the surface of the TFT circuit substrate 3 installed in the chamber 32.

  That is, the iodine evaporation source 35 heats the iodine evaporation source 35 to about 100 ° C., whereby the iodine inside the iodine evaporation source 35 vaporizes and releases iodine into the chamber 32. Iodine is adhered to the surface of the TFT circuit board 3 placed on the surface of the TFT circuit board 3 to form a thin film of iodine thin film layer 22 on the surface of the TFT circuit board 3.

  Further, the lead iodide evaporation source 36 heats the lead iodide evaporation source 36 to around 400 ° C., thereby evaporating the lead iodide inside the lead iodide evaporation source 36 and irradiating it in the chamber 32. Lead is released, lead iodide is adhered to the surface of the iodine thin film layer 22 formed on the surface of the TFT circuit board 3 installed in the chamber 32, and lead iodide is deposited on the surface of the iodine thin film layer 22. An X-ray photoconductive film 5 as a main component is formed.

  Furthermore, the lead evaporation source 37 is installed in the chamber 32 by heating the lead evaporation source 37 so that the lead in the lead evaporation source 37 is vaporized and released into the chamber 32. Lead is attached to the surface of the X-ray photoconductive film 5 formed on the surface of the TFT circuit substrate 3, and a lead thin film layer 24 is formed on the surface of the X-ray photoconductive film 5.

  Next, a method for manufacturing the X-ray detector according to the first embodiment will be described.

  First, the TFT circuit substrate 3 is formed by providing each pixel 2 on the holding substrate 11 with the thin film transistor 14, the charge storage capacitor 15, and the pixel electrode 13. The TFT circuit substrate 3 is manufactured using a manufacturing process used when manufacturing a general liquid crystal display device.

  Thereafter, the TFT circuit board 3 is installed inside the vacuum vapor deposition apparatus 31 shown in FIG. Then, the inside of the chamber 32 of the vacuum vapor deposition apparatus 31 is sufficiently evacuated using a vacuum pump 33.

  Then, when a sufficient degree of vacuum is achieved in the chamber 32, the TFT circuit substrate 3 is heated to a predetermined temperature using the substrate heating device.

  In this state, the iodine evaporation source 35 is heated to about 100 ° C., the iodine in the iodine evaporation source 35 is vaporized, and iodine molecules are released into the chamber 32.

  At this time, some of the iodine molecules released into the chamber 32 adhere to the surface of the TFT circuit substrate 3, and a thin film of iodine thin film layer 22 is formed on the surface of the TFT circuit substrate 3.

  Then, the heating of the iodine evaporation source 35 is continued, and when the iodine thin film layer 22 having a predetermined thickness is formed on the surface of the TFT circuit substrate 3, the heating of the iodine evaporation source 35 is stopped, and the chamber End the release of iodine molecules into 32.

  Thereafter, the lead iodide evaporation source 36 is heated to around 400 ° C. to vaporize lead iodide in the lead iodide evaporation source 36, and lead iodide molecules are released into the chamber 32.

  At this time, some of the lead iodide molecules released into the chamber 32 are attached to the surface of the iodine thin film layer 22 formed on the surface of the TFT circuit substrate 3, and the iodine thin film layer 22 is then iodinated on the surface. An X-ray photoconductive film 5 containing lead as a main component is formed.

  Then, the heating of the lead iodide evaporation source 36 is continued at the stage where the X-ray photoconductive film 5 having a predetermined thickness is formed on the surface of the iodine thin film layer 22 by continuing the heating of the lead iodide evaporation source 36. To stop the release of lead iodide molecules into the chamber 32.

  Thereafter, the lead evaporation source 37 is overheated to vaporize lead in the lead evaporation source 37 and release lead molecules into the chamber 32.

  At this time, some of the lead molecules released into the chamber 32 adhere to the surface of the X-ray photoconductive film 5, and a lead thin film layer 24 is formed on the surface of the X-ray photoconductive film 5.

  The lead evaporation source 37 is continuously overheated, and when the lead thin film layer 24 having a predetermined thickness is formed on the surface of the X-ray photoconductive film 5, the lead evaporation source 37 is stopped from being overheated. The release of lead molecules into the chamber 32 is terminated.

  Further, the bias electrode layer 6 is formed on the surface of the lead thin film layer 24 by using a general metal thin film forming technique such as sputter deposition to form the X-ray photoconductor layer 4.

As described above, according to the first embodiment, what is important when detecting an X-ray image in the direct X-ray detector 1 is the X-ray photoconductivity of the X-ray detector 1. This is a characteristic of the body layer 4. A heavy metal iodide typified by lead iodide (PbI ₂ ) used as the X-ray photoconductive film 5 of the X-ray photoconductor layer 4 is a kind of semiconductor, and a conductivity type which is an important characteristic in these semiconductors. The properties of these semiconductors are greatly affected by this control.

  In the X-ray photoconductive film 5 used in the direct X-ray detector 1, a bias electric field is applied from the outside in order to efficiently carry the pair of electrons e and holes h generated by the incident X-ray L to the outside. Need to be added. However, an unnecessary electric current flows from the bias electrode layer 6 and the pixel electrode 13 in contact with the X-ray photoconductive film 5 by this external bias electric field and is added to the X-ray image signal, so that a signal in the X-ray photoconductive film 5 is obtained. The SN ratio will deteriorate.

  Here, in order to prevent deterioration of the signal-to-noise ratio of the signal in the X-ray photoconductive film 5, the conductivity type in the vicinity of the pixel electrode 13 and the bias electrode layer 6 in the X-ray photoconductive film 5 is controlled, It is most effective to realize a PN junction inside the X-ray photoconductive film 5.

  Therefore, in order to realize a PN junction state inside the X-ray photoconductive film 5, an iodine thin film layer 22 is additionally formed at the interface between the X-ray photoconductive film 5 and the TFT circuit substrate 3, and this A lead thin film layer 24 is additionally formed at the interface between the X-ray photoconductive film 5 and the bias electrode layer 6. As a result, the components contained in each of the iodine thin film layer 22 and the lead thin film layer 24 are diffused in a very small amount inside the X-ray photoconductive film 5 by an operation such as heat treatment. Therefore, an iodine excess layer 23 containing an excessive iodine component is generated and formed in the vicinity of the TFT circuit substrate 3 in the X-ray photoconductive film 5, and the bias electrode in the X-ray photoconductive film 5 is formed. A lead-excess layer 25 containing an excessive amount of lead component is generated in the vicinity of the layer 6 and formed.

  At this time, in the X-ray photoconductive film 5 containing lead iodide as a main component, the ratio of lead to iodine is exactly 1 to 2. Accordingly, lead is in a divalent cation state and iodine is in a monovalent anion state. Therefore, in this X-ray photoconductive film 5, the balance between the cation and the anion is maintained as a whole. Become sexual. That is, in this neutral state, an intrinsic semiconductor state in which holes h and electrons e are arranged in a well-balanced manner inside the X-ray photoconductive film 5 is obtained.

  However, if the amount of lead in the X-ray photoconductive film 5 is made slightly excessive, the amount of iodine atoms, which are negative ions of electrons e possessed by excess lead atoms, is insufficient. Electrons e exist in the photoconductive film 5 in a floating state. Therefore, the presence of the excess electrons e causes the X-ray photoconductive film 5 in the vicinity of the bias electrode layer 6 to exhibit n-type conductivity, so that the lead-excess layer 25 exhibits n-type semiconductor properties. It becomes like this.

  Similarly, if the amount of iodine in the X-ray photoconductive film 5 is made slightly excessive, the amount of lead atoms supplying electrons to the excess iodine atoms is insufficient. The holes h exist in a floating state. Therefore, since the excess holes h exist, the X-ray photoconductive film 5 in the vicinity of the TFT circuit substrate 3 exhibits p-type conductivity, so that the iodine-excess layer 23 has the characteristics of a p-type semiconductor. As shown.

  Therefore, since the lead excess layer 25 and the iodine excess layer 23 exist above and below the X-ray photoconductive film 5, the X-ray photoconductive film 5 sandwiched between the lead excess layer 25 and the iodine excess layer 23 becomes p It becomes a pn junction state sandwiched between the n-type semiconductor and the n-type semiconductor.

  Here, the band gap of the X-ray photoconductive film 5 when each of the lead excess layer 25 and the iodine excess layer 23 does not exist will be described with reference to FIG. First, an electric field is formed between the pixel electrode 13 and the bias electrode layer 6 by the applied voltage 41 in order to take out holes h and electrons e generated in the X-ray photoconductive film 5 by incident X-rays L. . At this time, the energy level in the X-ray photoconductive film 5 is tilted by the electric field generated by the applied voltage 41, and a large tilt is generated.

  In this state, the electrons e generated in the X-ray photoconductive film 5 by the incident X-rays L are pulled up to the energy level 42 in the valence band and then attracted to an external electric field to reach the bias electrode layer 6. . Similarly, the holes h generated in the X-ray photoconductive film 5 by the incident X-ray L are pulled down to the energy level 42 in the valence band, reach the pixel electrode 13 by the electric field, and are extracted as a signal to the outside. .

  At this time, the electric field strength in the vicinity of the pixel electrode 13 is high due to the large inclination of the energy level 43 of the conductive band in the vicinity of the pixel electrode 13. For this reason, the electrons e leaking from the pixel electrode 13 into the X-ray photoconductive film 5 are accelerated by the electric field in the vicinity of the pixel electrode 13 and become a dark current unrelated to the incident X-ray L.

  Further, the same phenomenon occurs near the bias electrode layer 6. That is, since the electric field strength of the X-ray photoconductive film 5 in the vicinity of the bias electrode layer 6 is strong, the holes h leaking from the bias electrode layer 6 into the X-ray photoconductive film 5 It is accelerated by a nearby electric field and becomes a dark current unrelated to the incident X-ray L. The dark current generated here is mixed with the signal from the incident X-ray L that should be detected, and becomes a noise component, which degrades the signal quality.

  Therefore, the lead excess layer 25 and the iodine excess layer 23 are respectively provided above and below the X-ray photoconductive film 5, and the X-ray photoconductive film 5 is brought into a pn junction state by the lead excess layer 25 and the iodine excess layer 23. . At this time, the iodine excess layer 23 exhibits p-type conductivity, and the lead excess layer 25 functions as an n-type conductivity layer. For this reason, the X-ray photoconductive film 5 is in a pin junction state.

  As a result, the holes h generated in the iodine excess layer 23 and the electrons e generated in the lead excess layer 25 compensate each other to generate space charges. The band gap state of the X-ray photoconductive film 5 changes as shown in FIG. That is, the inclination of the energy level 44 of the conductive band near the pixel electrode 13 is reduced, and the inclination of the energy level 45 of the valence band near the bias electrode layer 6 is also reduced. As a result, the electric field strength in the vicinity of each of the pixel electrode 13 and the bias electrode layer 6 decreases, and the electrons e and holes h leaked from the pixel electrode 13 and the bias electrode layer 6 into the X-ray photoconductive film 5 Therefore, the generation of dark current can be reduced.

  Therefore, since the conductivity type in the X-ray photoconductive film 5 of the X-ray detector 1 can be easily controlled, the generation of dark current that degrades the quality of the X-ray image signal in the X-ray detector 1 can be reduced. . Therefore, the sensitivity of the X-ray photoconductive film 5 can be improved and unnecessary new synthesized components can be removed, so that the X-ray detector 1 can have high performance.

  Next, a second embodiment of the X-ray detector manufacturing apparatus of the present invention will be described with reference to FIG.

  The X-ray detector manufacturing apparatus shown in FIG. In this deposition apparatus 51, the material used as the X-ray photoconductive film 5 of the X-ray detector 1 is heavy metal iodide, and utilizes the properties of this heavy metal iodide. That is, heavy metal iodide is a salt companion and has a property of exhibiting a certain solubility in water and organic solvents.

  The deposition apparatus 51 includes a bottomed prismatic deposition container 52. The precipitation vessel 52 is filled with a lead iodide aqueous solution W and stored therein. Further, a lead iodide powder P as a raw material powder is submerged in the lead iodide aqueous solution W in the precipitation vessel 52 at the bottom of the precipitation vessel 52. A heating device 53 for heating the lead iodide aqueous solution W in the precipitation vessel 52 is attached to the lower portion of the precipitation vessel 52. Further, a cooling device 54 for cooling the TFT circuit substrate 3 is attached to the back surface of the TFT circuit substrate 3 that is inserted into the lead iodide aqueous solution W in the precipitation vessel 52 and immersed therein.

  Next, a method for manufacturing the X-ray detector according to the second embodiment will be described.

  First, after manufacturing the TFT circuit substrate 3 by the same method as in the first embodiment, an iodine thin film layer 22 on the surface of the TFT circuit substrate 3 and an X-ray photoconductive film thinner than the final film thickness. 5 and each.

  Thereafter, the cooling device 54 is attached to the back surface of the TFT circuit board 3, and then the TFT circuit board 3 is placed in the deposition container 52 with the surface of the TFT circuit board 3 facing the opening side of the deposition container 52. Immerse in filled lead iodide aqueous solution W. In this state, the lead iodide aqueous solution W in the precipitation vessel 32 is heated by the heating device 53.

  At this time, as the lead iodide saturation concentration in the lead iodide aqueous solution W increases, a part of the lead iodide powder P submerged in the lead iodide aqueous solution W dissolves in the lead iodide aqueous solution W.

  As a result, the lead iodide aqueous solution W in which lead iodide is newly dissolved by the rise in the water temperature of the lead iodide aqueous solution W is carried to the upper portion of the lead iodide aqueous solution W by thermal convection and diffusion, and the TFT circuit board 3. To the X-ray photoconductive film 5 formed on the surface of the film.

  At this time, since the TFT circuit substrate 3 is cooled by the cooling device 54 and kept at a low temperature, the lead iodide aqueous solution W in contact with the TFT circuit substrate 3 is also cooled. Accordingly, since the lead iodide saturation concentration in the lead iodide aqueous solution W is lowered by the change of the water temperature, the lead iodide concentration in the lead iodide aqueous solution W becomes supersaturated, and X-ray light is obtained as a lead iodide crystal. Deposited on the surface of the conductive film 5.

  That is, since a thin film of lead iodide is formed in advance as the X-ray photoconductive film 5 on the surface of the TFT circuit substrate 3, the lead iodide component that is supersaturated in the lead iodide aqueous solution W is preferential. Then, the crystal growth is performed using the lead iodide thin film on the TFT circuit substrate 3 as a crystal nucleus.

  Thereafter, the lead iodide aqueous solution W in which the temperature of the lead iodide crystal is lowered due to the precipitation of lead iodide crystals is transported to the lower portion of the precipitation vessel 52 by thermal convection and diffusion, and is heated again to form new one from the lead iodide powder P. By dissolving the lead iodide component, lead iodide crystals can be continuously deposited on the surface of the TFT circuit substrate 3.

  As a result, in the X-ray detector manufacturing method of the second embodiment, the manufacturing speed is slow, but all of the X-ray photoconductive film 5 is formed by the vacuum vapor deposition apparatus 31 of the first embodiment. Compared with the case where it does, since the utilization efficiency of a material can be improved, an expensive material can be utilized efficiently.

Note that, as in the third embodiment shown in FIG. 8, the heated lead iodide aqueous solution W is forcibly supplied from the supply port 55 opened at the lower portion of the deposition vessel 52 and applied to the surface of the TFT circuit substrate 3. If the amount of the lead iodide component to be supplied is increased, the manufacturing time of the X-ray photoconductive film 5 can be shortened. In addition, the X-ray detector manufacturing methods shown in the second and third embodiments described above include other materials for the X-ray photoconductive film 5, such as mercury iodide (HgI ₂ ), indium iodide (InI), and Even with heavy metal iodides such as bismuth iodide (BiI ₃ ), the X-ray photoconductive film 5 made of these materials can be sufficiently produced by changing the type and temperature of the solvent.

  In each of the above embodiments, the best combination in which lead iodide is used for the X-ray photoconductive film 5 and the lead thin film layer 24 and the iodine thin film layer 22 are provided above and below the X-ray photoconductive film 5 will be described. However, even if the iodine excess layer 23 and the lead excess layer 25 are turned upside down, the same effect can be obtained. Even when only one of the iodine excess layer 23 and the lead excess layer 25 is formed, a certain effect can be expected.

Further, as a material of the X-ray photoconductive film 5, even if heavy metal iodide such as mercury iodide (HgI ₂ ), indium iodide (InI) and bismuth iodide (BiI ₃ ) is contained as a main component, the cation The lead thin film layer 24 is changed to a metal element thin film layer in heavy metal iodide, that is, a mercury (Hg) thin film layer, a bismuth (Bi) thin film layer, and an indium (In) thin film layer, respectively. Thus, similar effects can be achieved.

  Moreover, although the X-ray detector 1 for detecting X-rays has been described, for example, even a radiation detector that detects various types of radiation other than X-rays such as γ-rays can be used correspondingly. Further, the pixels 2 on which the thin film transistors 14 and the pixel electrodes 13 are formed are two-dimensionally formed in a matrix on the holding substrate 11 of the TFT circuit substrate 3. The pixels 2 are one-dimensionally formed on the holding substrate 11. It may be provided.

It is explanatory sectional drawing which shows 1st Embodiment of the radiation detector of this invention. It is a description perspective view which shows a radiation detector same as the above. It is an explanatory top view which shows a radiation detector same as the above. It is explanatory drawing which shows the manufacturing apparatus of a radiation detector same as the above. It is explanatory drawing which shows the band cap of the radiation photoconductive layer which removed the semiconductor layer from the radiation detector same as the above. It is explanatory drawing which shows the band cap of the radiation photoconductive layer of a radiation detector same as the above. It is explanatory drawing which shows the manufacturing apparatus of the radiation detector of the 2nd Embodiment of this invention. It is explanatory drawing which shows the manufacturing apparatus of the radiation detector of the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray detector as a radiation detector 3 TFT circuit board as a circuit board 5 X-ray photoconductive film as a radiation photoconductive layer 6 Bias electrode layer as an electrode layer
13 Pixel electrode
22 Iodine thin film layer as the first thin film layer
24 Lead thin film layer as metal element thin film layer as second thin film layer

Claims (7)

A circuit board with pixel electrodes;
A radiation photoconductive layer provided on the pixel electrode of the circuit board for converting incident radiation into an electrical signal and containing metal iodide;
An electrode layer provided on the radiation photoconductive layer so as to face the pixel electrode;
A radiation detector comprising: the radiation photoconductive layer; and an iodine thin film layer provided between one of the electrode layer and the pixel electrode. A circuit board with pixel electrodes;
A radiation photoconductive layer provided on the pixel electrode of the circuit board for converting incident radiation into an electrical signal and containing metal iodide;
An electrode layer provided on the radiation photoconductive layer so as to face the pixel electrode;
A radiation detector comprising: the radiation photoconductive layer; and the metal element thin film layer in the metal iodide provided between any one of the electrode layer and the pixel electrode. The metal element thin film layer contains any one of lead (Pb), mercury (Hg), indium (In), and bismuth (Bi) as a metal element in the metal iodide. Radiation detector. The radiation photoconductive layer contains any one of lead iodide (PbI ₂ ), mercury iodide (HgI ₂ ), indium iodide (InI) and bismuth iodide (BiI ₃ ) as a metal iodide. The radiation detector according to claim 1. A circuit board with pixel electrodes;
A radiation photoconductive layer provided on the pixel electrode of the circuit board for converting incident radiation into an electrical signal and containing metal iodide;
An electrode layer provided on the radiation photoconductive layer so as to face the pixel electrode;
A first thin film layer provided between the electrode layer and the radiation photoconductive layer and containing any one of a metal element and iodine in the metal iodide;
A second thin film layer provided between the radiation photoconductive layer and the plurality of pixel electrodes and containing either the metal element or iodine;
The radiation detector characterized by comprising. The radiation photoconductive layer contains any one of lead iodide (PbI ₂ ), mercury iodide (HgI ₂ ), indium iodide (InI) and bismuth iodide (BiI ₃ ) as a metal iodide. The radiation detector according to claim 5. Either one of the first thin film layer and the second thin film layer contains one of lead (Pb), mercury (Hg), indium (In), and bismuth (Bi) as a metal element in the metal iodide. The radiation detector according to claim 5 or 6.

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