JP2006261203A - Photoconductive layer constituting radiation imaging panel and radiation imaging panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance residual characteristics of photoconduction in a photoconductive layer composed of Bi<SB>x</SB>MO<SB>y</SB>polycrystal. <P>SOLUTION: A photoconductive layer constituting a radiation imaging panel for recording radiation image information as an electrostatic latent image is a polycrystal composed of Bi<SB>x</SB>MO<SB>y</SB>(M is at least one kind of Ge, Si and Ti) wherein x satisfies following relation 11.1≤x≤11.95, and y is a stoichiometric number of oxygen atoms dependent on M and x. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiation imaging panel suitable for application to a radiation imaging apparatus such as an X-ray, and more particularly to a photoconductive layer constituting the radiation imaging panel.

  Conventionally, in medical X-ray photography, a photoconductive layer sensitive to X-rays has been used as a photoconductor to reduce the exposure dose received by subjects and improve diagnostic performance. An X-ray imaging panel that reads and records a recorded electrostatic latent image with light or multiple electrodes is known. These are superior in that the resolution is higher than the indirect photographing method using a TV image pickup tube which is a well-known photographing method.

  The X-ray imaging panel described above generates charges corresponding to X-ray energy by irradiating the charge generation layer provided in the imaging panel with X-rays, and reads the generated charges as an electrical signal. The photoconductive layer functions as a charge generation layer.

Bi ₁₂ MO ₂₀ (wherein M is at least one of Ge, Si, and Ti) has photoconductivity and dielectric properties, so its use as a photoconductive layer has been studied. Describes that Bi ₁₂ GeO ₂₀ and Bi ₁₂ SiO ₂₀ are used for the photoconductive layer. In general, it is considered that the crystal composition of Bi ₁₂ MO ₂₀ is the stoichiometric ratio. For example, in Patent Documents 2 and 3, Bi ₁₂ GeO ₂₀ and Bi having compositions of x = 12 and y = 20 are disclosed in Patent Documents 2 and 3. ₁₂ SiO ₂₀ is described.

On the other hand, in Non-Patent Document 1, when the composition of the melt was changed in the range of 10 ≦ x ≦ 14 and a Bi _x MO _y single crystal was grown, the single crystal grown in the melt with x = 11.5 was obtained. (The crystal composition ratio of this single crystal is about 12.15 and about 12.69 from the reading of the graph), and it is described that the photoconductive current becomes maximum. Non-Patent Document 2 discloses that a Bi _x GeO _y single crystal is obtained by changing the GeO ₂ content in the range of 9.0 to 20.0 mol% (9 ≦ x ≦ 20 in terms of x) with respect to the composition of the melt. ₂ Bi _x SiO _y single crystals were grown by changing the content in the range of 9.0 to 18.0 mol% (8 ≦ x ≦ 20 in terms of x), and μτ (product of carrier mobility and lifetime) of the grown single crystals. ) Was investigated.
JP-A-11-211832 JP-A-11-237478 JP 2000-249769 The Chemical Society of Japan, 1981 No.10 p.1630〜p.1639 Journal of Applied physics., Vol.94, No.4, p.2507-p.2509 (2003)

As a result of diligent study, the present inventor has found that contrary to the description in Patent Documents 2 and 3, the residual property of photoconduction can be improved when there is less bismuth than the crystal composition of the stoichiometric ratio that is normally considered. The present invention has been reached. Note that both Non-Patent Documents 1 and 2 described above are single crystal Bi _x MO _y , which has a very small grain boundary, which reduces dark current and increases the X-ray photoelectric flow rate. Although it is expected to improve, the manufacturing cost is high, and it is technically difficult to increase the area such as a size of several tens of centimeters for practical use. In addition, since it is difficult to control the composition of a single crystal, there is a problem that a single crystal having a desired composition cannot be obtained.

That is, the present invention provides a photoconductive layer made of a Bi _x MO _y polycrystal having improved photoconductive residual characteristics as a photoconductive layer constituting a radiation imaging panel that records radiation image information as an electrostatic latent image. It is for the purpose.

The photoconductive layer constituting the radiation imaging panel that records the radiographic image information of the present invention as an electrostatic latent image has a photoconductive layer of Bi _x MO _y (where M is at least one of Ge, Si, and Ti). The Bi _x MO _y is 11.1 ≦ x ≦ 11.95, and y is the stoichiometric number of oxygen atoms determined by M and x (y = 1.5x + 2). ).

  A polycrystal generally means a solid in which single crystals with different orientations are assembled, and the polycrystal here is a collection of single crystals with different orientations, such as sintering, aerosol deposition, vapor phase growth, etc. This means that the single crystals formed in the above are densely assembled and the crystals are bonded or bonded together, and do not contain a binder (binder) made of an organic material, a polymer material, or an inorganic material. .

The M is preferably Ti.
The Bi _x MO _y is preferably a sintered body. Here, the sintered body means a material formed by bonding or coalescence between constituent particles by heating a powder of Bi _x MO _{y at} a temperature below the melting point or at a temperature at which a small amount of liquid phase exists.

The radiation imaging panel of the present invention is a polycrystalline body made of Bi _x MO _{y that} records radiation image information as an electrostatic latent image, wherein _{x of the} Bi _x MO _y is 11.1 ≦ x ≦ 11.95, y is characterized by having a photoconductive layer having a stoichiometric number of oxygen atoms determined by M and x.

The photoconductive layer of the present invention is a polycrystalline body comprising a _{Bi x MO y, Bi x MO} x is 11.1 ≦ x ≦ 11.95 of _y, y is the stoichiometric oxygen atom determined by M and x Since it is a number, it is possible to improve the residual property of photoconduction. In the case of a 5 frames / second semi-moving image or a 5-30 frame / second moving image, there is a problem that the image becomes unclear or distorted when affected by the previously sensed electrical signal. since in the case of the photoconductive layer consisting of _x MO _y residual characteristics of the photoconductive are good, semi-video shall not susceptible to electrical signals sensed before in the case of employing a matter of course video It becomes possible.

Further, since the photoconductive layer of the present invention is a polycrystal, it can cope with an increase in the area of the photoconductive layer, and also suppresses the manufacturing cost of the photoconductive layer compared with single crystal Bi _x MO _y. be able to.

  In addition, since the photoconductive substance particles are in contact with each other, a reduction in the efficiency of collecting generated charges due to the presence of a binder as in a photoconductive layer formed by a coating method is suppressed, and electric noise is reduced. It is possible to improve the graininess of the image and improve the sensitivity.

In addition, when M is Ti or Bi _x MO _y is a sintered body, the effect of collecting generated charges can be further enhanced, and the sensitivity can be improved.

The photoconductive layer of the present invention, Bi _x MO a polycrystalline body comprising a _y, Bi _x MO _y of x is 11.1 ≦ x ≦ 11.95, y stoichiometric oxygen determined by M and x It is characterized by the number of atoms. If x deviates from this range, the residual characteristics of photoconductivity are reduced.

A polycrystalline body consisting _{Bi x MO y, Bi x MO} x is 11.1 ≦ x ≦ 11.95 of _y, y is the photoconductive layer is a stoichiometric oxygen atom number determined by M and x Can be produced by adjusting the composition ratio (molar ratio) of Bi and M of the raw material solution or powder shown below to the desired composition ratio of Bi _x MO _y crystals. it can.

As a specific method, first, a Bi _x MO _y precursor liquid is obtained by reacting a bismuth salt and a metal alkoxide under acidic conditions. The obtained Bi _x MO _y precursor liquid is applied to a support and dried. Examples thereof include a method of sintering a Bi _x MO _y film or a Bi _x MO _y precursor film formed in this way.

The bismuth salt is preferably bismuth nitrate or bismuth acetate, and the metal alkoxide is an alkoxide of Ge, Si, Ti, more specifically, Ge (O—CH ₃ ) ₄ , Ge (O—C ₂ H ₅ ). ₄ , Ge (O—iC ₃ H ₇ ) ₄ , Si (O—CH ₃ ) ₄ , Si (O—C ₂ H ₅ ) ₄ , Si (O—iC ₃ H ₇ ) ₄ , Ti (O—CH ₃₎ ) ₄ , Ti (O—C ₂ H ₅ ) ₄ , Ti (O—iC ₃ H ₇ ) _{4 and the} like can be preferably exemplified.

As a method of hydrolyzing a bismuth salt and a metal alkoxide under acidic conditions, it can be carried out by a known method as appropriate. For example, a bismuth salt and a metal alkoxide can be mixed with acetic acid, a mixed aqueous solution of methoxyethanol and nitric acid, It is preferable to hydrolyze with a mixed aqueous solution. After hydrolysis, a Bi _x MO _y precursor solution is obtained, but it is more preferable to perform concentration or reflux before applying this to the support.

In the case of sintering the Bi _x MO _y precursor film coated on the support, a stage on which the molded body is placed when the fired body (molded body) formed with the Bi _x MO _y precursor film is sintered. As the setter, it is preferable to use an oxide material, specifically, an aluminum oxide sintered body, a zirconium oxide sintered body, or a single crystal of aluminum oxide. By sintering using such a setter, the Bi _x MO _y sintered body can be manufactured without fusing with the setter. FIG. 1 is a schematic cross-sectional view showing a method for producing a Bi _x MO _y sintered body.

FIG. 1 shows a state before firing is started in which a body 1 to be fired is placed on a setter 2 that is shelved via a column 3. The to-be-fired body 1 is a flat molded body of a Bi _x MO _y precursor film. Setter 2 is an oxide material such as an aluminum oxide sintered body, a zirconium oxide sintered body, or a single crystal of aluminum oxide, and has a silicon oxide content of 1% by weight or less, and further 0.3% by weight or less. Is preferred.

A plurality of support columns 3 are arranged in the vicinity of the outer periphery of the setter at a predetermined interval. In addition, you may sinter in the state which mounted the weight board on the to-be-fired body at the time of sintering. The sintering temperature varies depending on the type of the body to be fired, the type of setter, the combination of the body to be fired and the setter, and the like, but cannot generally be said, but is preferably 800 ° C to 900 ° C. Usually, in the case of a setter made of a platinum material used for sintering, if sintering is performed at such a high temperature, fusion occurs between the setter and the sintered body, and the Bi _x MO _y sintered body is formed. Although it cannot be obtained, by using the oxide material for the setter 2, the fired body 1 can be formed without being fused to the setter 2.

As a method for producing the photoconductive layer of the present invention, secondly, Bi _x MO _y powder previously adjusted in a vacuum is wound up with a carrier gas, and the carrier gas mixed with the Bi _x MO _y powder is used. The aerosol deposition method (AD method) in which Bi _x MO _y powder is deposited by spraying on a support in a vacuum, and thirdly, the Bi _x MO _y powder is pressed at a high pressure using a press. And press sintering method to sinter the resulting film, and fourthly, a Bi _x MO _y powder is applied using a binder to produce a green sheet (a film containing the binder), and this green sheet is fired And a method of removing the binder and sintering the powder (hereinafter referred to as green sheet method).

As a method for preparing the Bi _x MO _y powder used in the production methods described in the second to fourth aspects, a Bi _x MO _y precursor liquid is obtained by hydrolyzing a bismuth salt and a metal alkoxide under acidic conditions. In addition, the Bi _x MO _y precursor liquid is concentrated to form a gel, and the gel Bi _x MO _y precursor is calcined to form a Bi _x MO _y powder. Bismuth oxide (Bi ₂ O ₃ ) and MO ₂ (Silicon oxide, germanium oxide, titanium oxide) are mixed and, for example, a method of obtaining a Bi _x MO _y powder by a solid phase reaction by pre-baking at 800 ° C., etc.

Although a binder is used in the green sheet method, this binder disappears completely by sintering and does not remain in the sintered Bi _x MO _y sintered body. Preferred examples of the binder used in the green sheet method include cellulose acetate, polyalkyl methacrylate, polyvinyl alcohol, and polyvinyl butyral.

  As the bismuth salt and the metal alkoxide, those described in the first production method can be preferably given, and the method for reacting the bismuth salt and the metal alkoxide under acidic conditions is also the one described in the first production method. Preferably it can be mentioned.

Above, Bi _x MO _y powder used in the second manufacturing method, bismuth and metal each alkoxide is reacted under alkaline conditions to obtain a Bi _x MO _y precursor liquid, the resulting Bi _x MO _y It can also be obtained by crystallizing the precursor liquid in the liquid phase.

Here, preferred examples of the bismuth alkoxide include Bi (O—CH ₃ ) ₃ , Bi (O—C ₂ H ₅ ) ₃ , Bi (O—iC ₃ H ₇ ) _3, etc. What was described by the said 1st manufacturing method can be mention | raise | lifted preferably. As a method of hydrolyzing the bismuth alkoxide and the metal alkoxide under alkaline conditions, a known method can be used as appropriate. Preferably, the bismuth alkoxide and the metal alkoxide are hydrolyzed together with sodium hydroxide, potassium hydroxide and the like. .

  The AD method described in the second manufacturing method is a technique in which fine particles and ultrafine particles prepared in advance are mixed with a carrier gas to be aerosolized and sprayed onto a substrate through a nozzle to form a film. Details of this method will be described with reference to FIG. FIG. 2 is a schematic diagram of a film forming apparatus for performing the AD method used for manufacturing the photoconductive layer of the present invention.

The manufacturing apparatus 10 includes an aerosol forming chamber 13 in which the Bi _x MO _y raw material particles 12 and the carrier gas are stirred and mixed, a film forming chamber 14 in which film formation is performed, and a high-pressure gas cylinder 15 that stores the carrier gas. The film forming chamber 14 includes a substrate 16 on which the Bi _x MO _y raw material particles 12 are deposited, a holder 17 that holds the substrate 16, a stage 18 that operates the holder 17 in three dimensions with XYZθ, and a Bi _{x on} the substrate 16. A nozzle 19 having a narrow opening for ejecting the MO _y raw material 12, a second pipe 20 connecting the nozzle 19 and the aerosolization chamber 13, and a second pipe connecting the aerosolization chamber 13 and the high-pressure gas cylinder 15. The pipe 21 and the vacuum pump 22 for reducing the pressure inside the film forming chamber 14 are configured.

The Bi _x MO _y raw material particles 12 in the aerosol forming chamber 13 are formed on the substrate 16 by the following procedure. The 0.1-2 μm Bi _x MO _y raw material particles 12 filled in the aerosolization chamber 13 together with the carrier gas introduced into the aerosolization chamber 13 through the second pipe 21 from the high-pressure gas cylinder 15 storing the carrier gas, Vibrated and agitated to be aerosolized. The aerosolized Bi _x MO _y raw material particles 12 pass through the first pipe 20 and are sprayed together with a carrier gas from a nozzle 19 having a narrow opening in the film forming chamber 14 to form a coating film. The film forming chamber 14 is evacuated by a vacuum pump 22, and the degree of vacuum in the film forming chamber 14 is adjusted as necessary. Further, since the holder of the substrate 16 can be moved three-dimensionally by the XYZθ stage 18, a Bi _x MO _y coating film having a necessary thickness is formed on a predetermined portion of the substrate 16.

  As the raw material particles, it is preferable to use powder having an average particle size of about 0.1 μm to 10 μm, and particles having a particle size of 0.1 to 2 μm are preferably 50% by weight or more. Here, the particle diameter means an equivalent volume sphere equivalent diameter which is the diameter of a sphere having the same volume as the particle, and the average is a number average.

The aerosolized raw material particles are easily accelerated to a flow rate of 2 to 300 m / sec by passing through a nozzle having a minute opening of 6 mm ² or less, and can be deposited on the substrate by colliding with the substrate by a carrier gas. Since the particles colliding with the carrier gas are bonded to each other by impact of the collision to form a film, a dense film is formed. The temperature of the substrate when depositing the raw material particles may be room temperature, but a denser film can be formed by adjusting the temperature to 100 ° C. to 300 ° C.

  The layer thickness of the photoconductive layer is preferably 10 to 700 μm, more preferably 80 to 300 μm. When the photoconductive layer thickness is less than 10 μm, the X-ray absorption rate decreases and no improvement in sensitivity can be expected. On the other hand, when the photoconductive layer is thicker than 700 μm, the X-ray absorption amount does not increase further due to saturation. Then, the generated electric charge moves a long distance until it reaches the electrode, and it is deactivated in the middle, and the collection efficiency is lowered. On the contrary, the image is deteriorated.

  In the radiation imaging panel, a direct conversion method in which radiation is directly converted into charges and stored, and radiation is converted into light once by a scintillator such as CsI, and the light is converted into charges by an a-Si photodiode and stored. Although there is an indirect conversion method, the photoconductive layer of the present invention can be used for the former direct conversion method. In addition to X-rays, γ rays, α rays, etc. can be used as radiation.

  In addition, the photoconductive layer of the present invention accumulates charges generated by radiation irradiation in a so-called optical reading system that reads by a radiation image detector using a semiconductor material that generates charges by light irradiation. It can also be used for a method (hereinafter referred to as “TFT method”) in which the charges are read by turning on and off an electrical switch such as a thin film transistor (TFT) one pixel at a time.

  First, a radiation imaging panel used for the former optical reading method will be described as an example. FIG. 3 is a sectional view showing an embodiment of a radiation imaging panel having a photoconductive layer according to the present invention.

  The radiation imaging panel 30 includes a first conductive layer 31 that is transparent to a recording radiation L1, which will be described later, and a recording radiation that exhibits conductivity when irradiated with the radiation L1 that has passed through the conductive layer 31. The conductive layer 32 and the charge charged to the conductive layer 31 (latent image polar charge; for example, negative charge) act as an insulator and have a charge opposite to the charge (transport polar charge; in the above example) For the positive charge), the charge transport layer 33 that acts as a substantially conductive material, the read photoconductive layer 34 that exhibits conductivity by irradiation of the read light L2 for reading described later, and the read light L2. The second conductive layer 35 having transparency is laminated in this order.

  Here, as the conductive layers 31 and 35, for example, a transparent glass plate in which a conductive substance is uniformly applied (nesa film or the like) is suitable. As the charge transport layer 33, the larger the difference between the mobility of the negative charge charged in the conductive layer 31 and the mobility of the positive charge having the opposite polarity, the better, poly N-vinylcarbazole (PVK), N, N Organic compounds such as' -diphenyl-N, N'-bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD) and discotic liquid crystals, or TPD polymers ( Polycarbonate, polystyrene, PVK) dispersion, semiconductor materials such as a-Se doped with 10 to 200 ppm of Cl are suitable. In particular, organic compounds (PVK, TPD, discotic liquid crystal, etc.) are preferable because they have light insensitivity, and since the dielectric constant is generally small, the capacitance of the charge transport layer 33 and the reading photoconductive layer 34 is reduced, so The signal extraction efficiency can be increased.

  The reading photoconductive layer 34 includes a-Se, Se-Te, Se-As-Te, metal-free phthalocyanine, metal phthalocyanine, MgPc (magnesium phtalocyanine), VoPc (phase II of vanadyl phthalocyanine), CuPc (Cupper phtalocyanine), and the like. Among them, a photoconductive material mainly containing at least one of them is preferable.

  For the recording radiation conductive layer 32, the photoconductive layer of the present invention is used. That is, the photoconductive layer of the present invention is a recording radiation conductive layer.

  Next, a system that uses light to read an electrostatic latent image will be briefly described. FIG. 4 is a schematic configuration diagram of a recording / reading system using the radiation imaging panel 30 (integrated electrostatic latent image recording device and electrostatic latent image reading device). This recording / reading system comprises a radiation imaging panel 30, a recording irradiation means 90, a power supply 50, a current detection means 70, a reading exposure means 92, and connection means S1, S2. The panel 30, the power supply 50, the recording irradiation means 90, and the connection means S 1, and the electrostatic latent image reading device portion includes the radiation imaging panel 30, the current detection means 70, and the connection means S 2.

  The conductive layer 31 of the radiation imaging panel 30 is connected to the negative electrode of the power source 50 via the connection means S1, and is also connected to one end of the connection means S2. One of the other ends of the connecting means S2 is connected to the current detecting means 70, and the conductive layer 35 of the radiation imaging panel 30, the positive electrode of the power source 50, and the other of the other ends of the connecting means S2 are grounded. The current detection means 70 includes a detection amplifier 70a made of an operational amplifier and a feedback resistor 70b, and constitutes a so-called current-voltage conversion circuit.

  A subject 29 is disposed on the upper surface of the conductive layer 31, and the subject 29 has a portion 29a that is transmissive to the radiation L1 and a blocking portion (light-shielding portion) 29b that is not transmissive. The recording irradiation means 90 uniformly exposes the radiation L1 to the subject 29, and the reading exposure means 92 scans and exposes the reading light L2 such as infrared laser light, LED, EL or the like in the direction of the arrow in FIG. Therefore, it is desirable that the reading light L2 has a beam shape converged to a small diameter.

  Hereinafter, an electrostatic latent image recording process in the recording / reading system having the above-described configuration will be described with reference to a charge model (FIG. 5). In FIG. 4, the connection means S2 is opened (not connected to either the ground or current detection means 70), the connection means S1 is turned on, and the DC voltage Ed from the power source 50 is applied between the conductive layer 31 and the conductive layer 35. Then, a negative charge is applied to the conductive layer 31 and a positive charge is applied to the conductive layer 35 from the power supply 50 (see FIG. 3A). As a result, a parallel electric field is formed between the conductive layers 31 and 35 in the radiation imaging panel 10.

  Next, the radiation L1 is uniformly irradiated toward the subject 29 from the recording irradiation means 90. The radiation L1 passes through the transmission part 29a of the subject 29 and further passes through the conductive layer 31. The radiation conductive layer 32 receives the transmitted radiation L1 and exhibits conductivity. This is understood by acting as a variable resistor that shows a variable resistance value according to the dose of radiation L1, and the resistance value is caused by the generation of a charge pair of electrons (negative charge) and holes (positive charge) by radiation L1. The resistance value is large when the dose of the radiation L1 transmitted through the subject 29 is small (see FIG. 5B). The negative charge (−) and the positive charge (+) generated by the radiation L1 are represented by enclosing − or + in circles in the drawing.

  The positive charge generated in the radiation conductive layer 32 moves at high speed in the radiation conductive layer 32 toward the conductive layer 31, and the negative charge is charged in the conductive layer 31 at the interface between the conductive layer 31 and the radiation conductive layer 32. And disappear after charge recombination (see FIGS. 5C and 5D). On the other hand, the negative charges generated in the radiation conductive layer 32 move in the radiation conductive layer 32 toward the charge transfer layer 33. Since the charge transfer layer 33 acts as an insulator for charges of the same polarity as the charges charged in the conductive layer 31 (in this example, negative charges), the negative charges that have moved through the radiation conductive layer 32 are radiation. It stops at the interface between the conductive layer 32 and the charge transfer layer 33 and accumulates at this interface (see FIGS. 5C and 5D). The amount of charge accumulated is determined by the amount of negative charge generated in the radiation conductive layer 32, that is, the dose of radiation L1 transmitted through the subject 29.

  On the other hand, since the radiation L1 does not pass through the light shielding part 29b of the subject 29, the portion corresponding to the lower part of the light shielding part 29b of the radiation imaging panel 30 does not change at all (see FIGS. 5B to 5D). In this way, by exposing the subject 29 to the radiation L1, charges according to the subject image can be accumulated at the interface between the radiation conductive layer 32 and the charge transfer layer 33. The subject image based on the accumulated charges is called an electrostatic latent image.

  Next, an electrostatic latent image reading process will be described with reference to a charge model (FIG. 6). The connection means S1 is opened to stop the power supply, and S2 is temporarily connected to the ground side, and the conductive layers 31 and 35 of the radiation imaging panel 30 on which the electrostatic latent image is recorded are charged to the same potential to recharge the charge. After the arrangement (see FIG. 6A), the connecting means S2 is connected to the current detecting means 70 side.

  When the reading light L2 is scanned and exposed to the conductive layer 35 side of the radiation imaging panel 30 by the reading exposure means 92, the reading light L2 passes through the conductive layer 35, and the photoconductive layer 34 irradiated with the transmitted reading light L2 is Conductivity is exhibited according to scanning exposure. This is dependent on the fact that the radiation conductive layer 32 is exposed to the radiation L1 to generate positive and negative charge pairs, and has a positive and negative charge pair upon receiving the reading light L2. (See FIG. 6B). As in the recording process, negative charges (−) and positive charges (+) generated by the reading light L2 are represented by enclosing − or + in circles in the drawing.

  Since the charge transport layer 33 acts as a conductor for the positive charge, the positive charge generated in the photoconductive layer 34 moves rapidly in the charge transport layer 33 so as to be attracted to the accumulated charge, The accumulated charge and charge recombination disappear at the interface between the radiation conductive layer 32 and the charge transport layer 33 (see FIG. 6C). On the other hand, the negative charge generated in the photoconductive layer 34 is recombined with the positive charge of the conductive layer 35 and disappears (see FIG. 6C). The photoconductive layer 34 is scanned and exposed with a sufficient amount of light by the reading light L2, and the accumulated charge accumulated at the interface between the radiation conductive layer 32 and the charge transport layer 33, that is, the electrostatic latent image is all charge recombined. Will be extinguished. Thus, the disappearance of the charge accumulated in the radiation imaging panel 30 means that the current I has flowed to the radiation imaging panel 30 due to the movement of the charge, and this state is the radiation imaging panel 30. Can be expressed by an equivalent circuit as shown in FIG. 6D, in which the current amount is expressed by a current source whose amount depends on the accumulated charge amount.

  In this way, by detecting the current flowing out from the radiation imaging panel 30 while scanning and exposing the reading light L2, it is possible to sequentially read the accumulated charge amount of each scanning-exposed part (corresponding to the pixel). The electrostatic latent image can be read. The operation of the radiation detection unit is described in Japanese Patent Application Laid-Open No. 2000-105297.

  Next, the latter TFT type radiation imaging panel will be described. This radiation imaging panel has a structure in which a radiation detection unit 100 and an active matrix array substrate (hereinafter referred to as an AMA substrate) 200 are joined as shown in FIG. As shown in FIG. 8, the radiation detection unit 100 is roughly divided into a common electrode 103 for applying a bias voltage and light that generates carriers that are electron-hole pairs in response to the radiation to be detected in order from the radiation incident side. The conductive layer 104 and the detection electrode 107 for collecting carriers are stacked. The radiation detection unit support 102 may be provided on the upper layer of the common electrode.

  The photoconductive layer 104 is the photoconductive layer of the present invention. The common electrode 103 and the detection electrode 107 are made of a conductive material such as ITO (indium tin oxide), Au, or Pt, for example. Depending on the polarity of the bias voltage, a hole injection blocking layer and an electron injection blocking layer may be attached to the common electrode 103 and the detection electrode 107.

  The configuration of each part of the AMA substrate 200 will be briefly described. As shown in FIG. 9, the AMA substrate 200 is provided with a capacitor 210 as a charge storage capacitor and one TFT 220 as a switching element for each of the radiation detection portions 105 corresponding to pixels. In the support 102, the radiation detection units 105 corresponding to the pixels are two-dimensionally arranged in a matrix configuration of about 1000 to 3000 × 1000 to 3000 in accordance with the required pixels, and the AMA substrate 200 also has pixels. The same number of capacitors 210 and TFTs 220 are two-dimensionally arranged in the same matrix configuration. The electric charge generated in the photoconductive layer is accumulated in the capacitor 210 and becomes an electrostatic latent image corresponding to the optical reading method. In the TFT method, an electrostatic latent image generated by radiation is held in a charge storage capacitor.

  Specific configurations of the capacitor 210 and the TFT 220 in the AMA substrate 200 are as shown in FIG. That is, the AMA substrate support 230 is an insulator, and the connection-side electrode 210b of the capacitor 210 and the TFT 220 are disposed on the ground electrode 210a of the capacitor 210 and the gate electrode 220a of the TFT 220 formed on the surface thereof via the insulating film 240. In addition to the source electrode 220b and the drain electrode 220c being stacked, the outermost surface side is covered with a protective insulating film 250. Further, the connection side electrode 210b and the source electrode 220b are connected to each other and are formed simultaneously. As the insulating film 240 constituting both the capacitor insulating film of the capacitor 210 and the gate insulating film of the TFT 220, for example, a plasma SiN film is used. The AMA substrate 200 is manufactured by using a thin film forming technique or a fine processing technique used for manufacturing a liquid crystal display substrate.

  Subsequently, the joining of the radiation detection unit 100 and the AMA substrate 200 will be described. With the detection electrode 107 and the connection side electrode 210b of the capacitor 210 aligned, both substrates 100 and 200 are made of anisotropic conductive film (ACF) containing conductive particles such as silver particles and having conductivity only in the thickness direction. The substrates 100 and 200 are mechanically combined by heating and pressurizing and bonding together, and at the same time, the detection electrode 107 and the connection side electrode 210b are electrically connected by the interposition conductor 140. .

  Further, the AMA substrate 200 is provided with a read drive circuit 260 and a gate drive circuit 270. As shown in FIG. 9, the read drive circuit 260 is connected to a read wiring (read address line) 280 in the vertical (Y) direction connecting the drain electrodes of the TFTs 220 having the same column, and the gate drive circuit 270 has a row. A horizontal (X) direction read line (gate address line) 290 connecting the gate electrodes of the same TFT 220 is connected. Although not shown, one preamplifier (charge-voltage converter) is connected to one readout wiring 280 in the readout drive circuit 260. As described above, the read driving circuit 260 and the gate driving circuit 270 are connected to the AMA substrate 200. However, an integrated circuit in which the read drive circuit 260 and the gate drive circuit 270 are integrally formed in the AMA substrate 200 is also used.

The radiation detection operation by the radiation imaging apparatus in which the radiation detector 100 and the AMA substrate 200 are joined and combined is described in, for example, Japanese Patent Application Laid-Open No. 11-287862.
Examples of the photoconductive layer constituting the radiation imaging panel of the present invention are shown below.

Example 1
Bismuth oxide (Bi ₂ O ₃ ) powder and titanium oxide (TiO ₂ ) powder were blended so that Bi: Ti = 11.9: 1, and ball mill mixing was performed in ethanol using zirconium oxide balls. Thereafter, the powder was recovered, dried, pre-baked at 800 ° C. for 8 hours, and Bi _11.9 TiO _19.85 powder was synthesized by a solid phase reaction between bismuth oxide and titanium oxide. The Bi _11.9 TiO _19.85 powder was roughly pulverized to 150 μm or less with a mortar, and then pulverized and dispersed in a ball mill in ethanol using zirconium oxide balls. At this time, 0.4 wt% polyvinyl butyral (PVB) was added as a dispersant for promoting dispersion. Thereafter, 3.7 wt% polyvinyl butyral as a binder and 0.8 wt% dioctyl phthalate as a plasticizer were added, and then a ball mill was continued to prepare a slurry for sheet molding. After the ball mill mixing, the recovered slurry was defoamed and concentrated by vacuum defoaming to adjust the viscosity of the slurry.

The slurry whose viscosity was adjusted was coated on a film base with a release agent using a coater and molded into a sheet. The molded body was left to dry at room temperature for 24 hours, and then peeled off from the film base. The peeled sheet molding was placed on a sapphire single crystal and sintered in an Ar atmosphere at a sintering temperature of 820 ° C. to obtain a Bi _11.9 TiO _19.85 sintered body. About 0.3 g of this sintered body was thermally decomposed with nitric acid and sulfuric acid and dissolved with dilute nitric acid to obtain a constant volume. After the obtained solution was appropriately diluted with dilute nitric acid, the Bi: Ti composition ratio was measured twice by ICP emission spectroscopic analysis (Seiko Instruments, sequential ICP emission spectroscopic analyzer). : Ti = 11.9: 1.

(Example 2)
A Bi _11.6 TiO _19.4 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and titanium oxide powder were blended so that Bi: Ti = 11.6: 1. Further, when the Bi: Ti composition ratio of the sintered body was measured twice in the same manner as in Example 1, Bi: Ti = 11.6: 1 in both cases.

(Example 3)
A Bi _11.3 TiO _18.95 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and titanium oxide powder were blended so that Bi: Ti = 11.3: 1. Further, when the Bi: Ti composition ratio of the sintered body was measured twice in the same manner as in Example 1, Bi: Ti = 11.3: 1 in both cases.

Example 4
A Bi _11.1 TiO _18.65 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and titanium oxide powder were mixed so that Bi: Ti = 11.1: 1. Further, when the Bi: Ti composition ratio of the sintered body was measured twice in the same manner as in Example 1, Bi: Ti = 11.1: 1 in both cases.

(Example 5)
A Bi _11.9 SiO _19.85 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and silicon oxide (SiO ₂ ) powder were mixed so that Bi: Si = 11.9: 1. About 0.1 g of this sintered body was decomposed by heating with nitric acid, and pure water was added to separate the filtrate (the filtrate was kept at a constant volume). At this time, the insoluble matter was melted with sodium carbonate and dissolved with dilute nitric acid to obtain a constant volume. The resulting solution was appropriately diluted with dilute nitric acid, and then the Bi: Si composition ratio was measured twice with the same ICP emission spectroscopic analyzer as in Example 1. Both were Bi: Si = 11.9: 1. .

(Example 6)
A Bi _11.6 SiO _19.4 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and silicon oxide powder were mixed so that Bi: Si = 11.6: 1. Further, when the Bi: Si composition ratio of the sintered body was measured twice in the same manner as in Example 5, Bi: Si = 11.6: 1 was measured twice.

(Example 7)
A Bi _11.3 SiO _18.95 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and silicon oxide powder were mixed so that Bi: Si = 11.3: 1. Further, when the Bi: Si composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Si = 11.3: 1 in both cases.

(Example 8)
A Bi _11.1 SiO _18.65 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and silicon oxide powder were blended so that Bi: Si = 11.1: 1. Further, when the Bi: Si composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Si = 11.1: 1 in both cases.

Example 9
A Bi _11.9 GeO _19.85 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and germanium oxide (GeO ₂ ) powder were blended so that Bi: Ge = 11.9: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Ge = 11.9: 1 in both cases.

(Example 10)
A Bi _11.6 GeO _19.4 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and germanium oxide powder were mixed so that Bi: Ge = 11.6: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Ge = 11.6: 1 in both cases.

(Example 11)
A Bi _11.3 GeO _18.95 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and germanium oxide powder were mixed so that Bi: Ge = 11.3: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, Bi: Ge = 11.3: 1 in both cases.

(Example 12)
A Bi _11.1 GeO _18.65 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and germanium oxide powder were mixed so that Bi: Ge = 11.1: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Ge = 11.1: 1 in both cases.

(Comparative Example 1)
A Bi ₁₂ TiO ₂₀ sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and titanium oxide powder were blended so that Bi: Ti = 12.0: 1. Further, when the Bi: Ti composition ratio of the sintered body was measured twice in the same manner as in Example 1, Bi: Ti = 12.0: 1 in both cases.

(Comparative Example 2)
A Bi ₁₁ TiO _18.5 sintered body was produced in the same manner as in Example 1 except that bismuth oxide powder and titanium oxide powder were blended so that Bi: Ti = 11.0: 1. Further, when the Bi: Ti composition ratio of the sintered body was measured twice in the same manner as in Example 1, Bi: Ti = 11.0: 1 in both cases.

(Comparative Example 3)
A Bi ₁₂ SiO ₂₀ sintered body was produced in the same manner as in Example 1 except that titanium oxide powder and silicon oxide powder were blended so that Bi: Si = 12.0: 1. Further, when the Bi: Si composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Si = 12.0: 1 in both cases.

(Comparative Example 4)
A Bi ₁₁ SiO _18.5 sintered body was produced in the same manner as in Example 1 except that titanium oxide powder and silicon oxide powder were blended so that Bi: Si = 11.0: 1. Further, when the Bi: Si composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Si = 11.0: 1 in both cases.

(Comparative Example 5)
A Bi ₁₂ GeO ₂₀ sintered body was produced in the same manner as in Example 1 except that titanium oxide powder and germanium oxide powder were blended so that Bi: Ge = 12.0: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Ge = 12.0: 1 in both cases.

(Comparative Example 6)
A Bi ₁₁ GeO _18.5 sintered body was produced in the same manner as in Example 1 except that titanium oxide powder and germanium oxide powder were blended so that Bi: Ge = 11.0: 1. Further, when the Bi: Ge composition ratio of the sintered body was measured twice in the same manner as in Example 5, it was Bi: Ge = 11.0: 1 in both cases.

  The sintered bodies completed in Examples 1 to 12 and Comparative Examples 1 to 6 were joined to an Al substrate using conductive paste dotite (manufactured by Fujikura Kasei), and the upper electrode was formed by sputtering Au with a thickness of 60 nm. The detection part of the radiation imaging panel provided with the photoconductive layer was completed. The X-ray photocurrent signal is obtained by irradiating the sample with 30mR X-ray for 0.1 seconds under the condition of voltage 80kV, converting the pulsed photocurrent generated under the applied voltage condition into voltage with a current amplifier, and using a digital oscilloscope. It was measured. The applied voltage was applied so as to correspond to an electric field of 1.5 V / μm. The maximum photocurrent during X-ray irradiation (photocurrent immediately before X-ray cutoff) was measured, and then the photocurrent after 300 msec after X-ray cutoff was measured.

The results are shown in Table 1. The measured value was shown by the photocurrent after 300 msec after the X-ray cutoff with respect to the maximum photocurrent during X-ray irradiation. In addition, the relative value of each Bi ₁₂ MO ₂₀ relative to the maximum photocurrent during X-ray irradiation, with the photocurrent after 300 msec after X-ray cutoff being 1.0, and Bi ₁₂ TiO ₂₀ during X-ray irradiation The relative value is shown with the photocurrent after 300 msec after the X-ray cutoff with respect to the maximum photocurrent being 1.0.

As is clear from Table 1, the photoconductive layer made of Bi _x MO _y of the present invention has a small photocurrent after 300 msec after X-ray blocking with respect to the maximum photocurrent during X-ray irradiation, and improves the residual characteristics of photoconduction. It was possible to make it. Therefore, a clear image can be obtained even when the image becomes unclear or disturbed when affected by an electrical signal previously sensed, such as a semi-moving image or moving image.

As described above, the photoconductive layer of the present invention, Bi _x MO a polycrystalline body comprising a _y, Bi _x MO x is 11.1 ≦ x ≦ 11.95 of _y, y is a chemical which is determined by M and x Because of the stoichiometric number of oxygen atoms, it is possible to improve the residual characteristics of photoconduction. And since it is a polycrystal, it can respond to the enlargement of a photoconductive layer. Furthermore, since no binder is present like the photoconductive layer formed by the coating method, the reduction in the efficiency of collecting generated charges is suppressed, electrical noise can be reduced, and the graininess of the image is improved. In addition, the sensitivity can be improved.

Schematic constitutional sectional view showing a method for producing a Bi _x MO _y sintered body Schematic schematic diagram of a production apparatus used in the photoconductive layer production method of the present invention Sectional drawing which shows one Embodiment of the radiation imaging panel which has a photoconductive layer manufactured with the manufacturing method of this invention Schematic configuration diagram of a recording and reading system using a radiation imaging panel Diagram showing the electrostatic latent image recording process in a recording and reading system using a charge model Diagram showing the electrostatic latent image reading process in the recording and reading system using a charge model Schematic diagram showing the combined state of the radiation detector and the AMA substrate Electrical circuit diagram showing equivalent circuit of AMA substrate Schematic cross-sectional view showing the pixels of the radiation detector

Explanation of symbols

1 To-be-fired body (molded body)
2 setters 3 props
10 Photoconductive layer manufacturing equipment
12 Bi _x MO _y raw material particles
13 Aerosolization chamber
14 Film forming chamber
15 High pressure gas cylinder
16 substrate
17 Holder
18 stages
19 nozzles
30 Radiation imaging panel
31 Conductive layer
32 Radiation conductive layer for recording
33 Charge transport layer
34 Photoconductive layer for recording
35 Conductive layer
70 Current detection means

Claims (4)

A photoconductive layer constituting a radiation imaging panel that records radiation image information as an electrostatic latent image, wherein the photoconductive layer is Bi _x MO _y (where M is at least one of Ge, Si, and Ti). ), Wherein _{x of the} Bi _x MO _y is 11.1 ≦ x ≦ 11.95, and y is the stoichiometric number of oxygen atoms determined by M and x. Photoconductive layer.   The photoconductive layer according to claim 1, wherein M is Ti. 3. The photoconductive layer according to claim 1, wherein the Bi _x MO _y is a sintered body. A radiation imaging panel comprising a photoconductive layer made of Bi _x MO _{y according} to claim 1, 2 or 3 for recording radiation image information as an electrostatic latent image.

Images