JP2006124272A - Process for producing photo-conductor layer for constituting radiation imaging panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Bi<SB>12</SB>MO<SB>20</SB>sintered material (wherein, M is at least one kind of Ge, Si, and Ti) almost free from crystal defects and having high sensitivity. <P>SOLUTION: When the Bi<SB>12</SB>MO<SB>20</SB>sintered material for constituting a radiation imaging panel, capable of recording radiation image information as an electrostatic latent image, is produced, sintering is performed in an inert gas atmosphere. Alternatively, the sintering is performed at a sintering temperature falling within the range of 800 to 900 °C and in an atmosphere in which the oxygen partial pressure P<SB>O2</SB>(Pa) satisfies the condition: 10<SP>-3</SP>≤P<SB>O2</SB>≤10<SP>-1</SP>. <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 method for producing 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. Conventionally, amorphous selenium has been used as the photoconductive layer. However, since amorphous selenium generally has a low X-ray absorption rate, the photoconductive layer needs to be formed thick (for example, 500 μm or more).

  However, as the film thickness increases, the charge collection efficiency decreases, so it is necessary to apply a high voltage to the photoconductive layer, but this tends to generate charges due to dark current, reducing the contrast in the low-dose region, and the device There is a problem of causing deterioration. There is also a problem that it is easy to pick up noise (structure noise) caused by fluctuations in the thickness direction of selenium. Furthermore, since the photoconductive layer is usually formed by vapor deposition, it takes a considerable amount of time to grow the photoconductive layer until the thickness becomes as described above, and its management is difficult. This eventually increases the manufacturing cost, leading to an increase in the cost of the X-ray imaging panel.

Because of these problems, materials for photoconductive layers other than selenium have been studied. For example, in Patent Documents 1 and 2, as a substance constituting the photoconductive layer, a composition formula Bi _x MO _y (where M is at least one of Ge, Si, and Ti, and x is 10 ≦ x ≦ 14). Wherein y represents the stoichiometric number of oxygen atoms by M and x.). According to this bismuth oxide composite oxide, it can be expected to improve the X-ray charge conversion efficiency.

  However, in Patent Documents 1 and 2, the photoconductive layer is formed by sintering a sol or gel obtained by hydrolyzing bismuth and a metal alkoxide, and dispersing and coating the sol or gel. Therefore, there is a limit to the photoconductive material filling rate of the photoconductive layer that can be formed by coating. In addition, the photoconductive layer formed by coating has a problem that the effect of preventing the movement of the generated charges by the binder is large and the electric noise becomes large, so that the graininess of the image is deteriorated.

On the other hand, Non-Patent Documents 1 and 2 describe a method for producing a Bi ₁₂ MO ₂₀ sintered body by a solid phase method. Since the Bi ₁₂ MO ₂₀ sintered body obtained by sintering has a dense structure as compared with that formed by coating, the photoconductive material filling rate of the photoconductive layer can be increased, and thus the sensitivity is improved. It is considered possible. However, in the methods described in Non-Patent Documents 1 and 2, the filling rate is increased as compared with the coating formation, but the sensitivity cannot be improved as expected.

Incidentally, in the field of ceramics, it is known that the oxidation state of an oxide is determined by the oxygen partial pressure, and the oxygen concentration in the atmosphere is determined by the ratio of CO gas to CO ₂ gas (Non-patent Document 3). . Non-Patent Document 3 includes N ₂ gas as a main component in the sintering process of the multilayer ceramic capacitor, and the oxygen partial pressure is controlled by at least one of H ₂ , H ₂ O, CO ₂ and CO. How to do is described.
JP-A-11-237478 JP 2000-249769 JP 2004-39892 A J.Am.Ceram.Soc. 84,2900 (2001) Ceramic.Bulletin 58,613 (1979) “Ceramic Engineering Handbook” (2nd edition), Japan Ceramic Society, p423-p426

The present inventor obtained a Bi ₁₂ MO ₂₀ sintered body free from defects that hinders the movement of charges by examining the conditions for manufacturing the Bi ₁₂ MO ₂₀ sintered body, and this was used as a photoconductive layer. It was considered that a radiation imaging panel with high sensitivity could be obtained by using it, and the present invention was achieved.

  That is, an object of the present invention is to provide a novel method for producing a photoconductive layer comprising a bismuth oxide-based composite oxide.

Bi ₁₂ MO ₂₀ sintered body (provided that M is at least one of Ge, Si, and Ti, which constitutes a radiation imaging panel that records radiation image information of the present invention as an electrostatic latent image. Is omitted)), the Bi ₁₂ MO ₂₀ sintered body is sintered in an inert gas atmosphere.

The inert gas means N ₂ gas or a rare gas (helium, argon), and is preferably a rare gas. The inert gas atmosphere is an atmosphere composed of N ₂ gas, rare gas, or a mixed gas of N ₂ gas and rare gas, and causes crystal defects in the sintering reaction when the Bi ₁₂ MO ₂₀ sintered body is manufactured. If it is within the range, it means that other atmospheric gases such as oxygen may be included. In particular, the oxygen partial pressure in the inert gas atmosphere is preferably in the range of 1 × 10 ⁻⁵ Pa to 20 Pa. The sintering may be performed in a sintering furnace using a metal muffle. Here, muffle means a device that shields a space for sintering with a material having high fire resistance and high thermal conductivity. In the present invention, a metal muffle using a metal for the material is sintered. It is preferable to use it.

A second method for producing a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered body, which constitutes a radiation imaging panel that records the radiation image information of the present invention as an electrostatic latent image, is the Bi ₁₂ MO ₂₀ sintered body. Sintering is performed in an atmosphere where the sintering temperature is 800 ° C. to 900 ° C. and the oxygen partial pressure P _O2 (Pa) is 10 ⁻³ ≦ P _O2 ≦ 10 ⁻¹ .

More preferably, the sintering is performed in an atmosphere where the ratio of the carbon monoxide partial pressure _PCO and the carbon dioxide partial pressure _PCO2 is 10 ⁻⁶ ≦ _PCO / _PCO2 ≦ 10 ⁻⁴ .

The first method for producing a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered body, which constitutes a radiation imaging panel for recording radiation image information of the present invention as an electrostatic latent image, is a method of firing a Bi ₁₂ MO ₂₀ sintered body. Since the sintering is performed in an inert gas atmosphere, there are fewer crystal defects than the Bi ₁₂ MO ₂₀ sintered body obtained by the conventional sintering. Therefore, by using this for the photoconductive layer, a highly sensitive radiation imaging panel Can be obtained.

A second method for producing a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered body, which constitutes a radiation imaging panel that records the radiation image information of the present invention as an electrostatic latent image, is a method of firing a Bi ₁₂ MO ₂₀ sintered body. Since the sintering is performed in an atmosphere where the sintering temperature is 800 ° C. to 900 ° C. and the oxygen partial pressure P _O2 (Pa) is 10 ⁻³ ≦ P _O2 ≦ 10 ⁻¹ , Bi ₁₂ MO obtained by conventional sintering is used. Compared with ₂₀ sintered bodies, there are fewer crystal defects. Therefore, by using this for the photoconductive layer, a highly sensitive radiation imaging panel can be obtained.

When sintering is performed in an atmosphere where the ratio of carbon monoxide partial pressure _PCO and carbon dioxide partial pressure _PCO2 is 10 ⁻⁶ ≦ _PCO / _PCO2 ≦ 10 ⁻⁴ , Bi ³⁺ → Bi It becomes possible to further suppress the oxidation of ⁵⁺ , and a Bi ₁₂ MO ₂₀ sintered body with few crystal defects can be manufactured.

The first method for producing a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered body, which constitutes a radiation imaging panel for recording radiation image information of the present invention as an electrostatic latent image, is a method of firing a Bi ₁₂ MO ₂₀ sintered body. The crystallization is performed in an inert gas atmosphere. FIG. 1 shows a schematic cross-sectional view of an apparatus for producing the Bi ₁₂ MO ₂₀ sintered body of the present invention.

The apparatus shown in FIG. 1 includes a sintering furnace 3 provided with a setter 2 on which a Bi ₁₂ MO ₂₀ molded body 1 is placed, heaters 4 provided above and below the sintering furnace 3, and atmosphere in the sintering furnace 3. Alternatively, the flow path 8 for feeding the inert gas and the flow path 9 for exhausting the atmosphere or the inert gas in the sintering furnace 3, the opposite side of the flow path 8 connected to the sintering furnace 3. The three-way valve 5 is provided with a flow path 6 for sending air to the three-way valve 5 and a flow path 7 for sending inert gas. The sintering furnace 3 is preferably a sintering furnace using a metal muffle. When a sintering furnace using a metal muffle is used, the oxygen partial pressure can be further reduced. In particular, when it is difficult to achieve an oxygen partial pressure of 10 ⁻³ Pa, which is the lower limit of a small amount of oxygen partial pressure contained as an impurity in the inert gas, a sintering furnace using a metal muffle is used. Thus, an oxygen partial pressure near this lower limit can be easily realized.

Molded body 1 is a flat molded body of Bi ₁₂ MO ₂₀ sintered body (which becomes a photoconductive layer after being sintered), and bismuth oxide and silicon oxide or germanium oxide. Alternatively, after mixing titanium oxide powder, Bi ₁₂ MO ₂₀ powder obtained by pre-baking is formed by a forming method such as a press forming method or a doctor blade method.

  The procedure for sintering the molded body will be described with reference to FIG. After the molded body 1 is placed on the setter 2, the three-way valve 5 is operated so that the flow path 6 and the flow path 8 are connected, and the atmosphere is sent into the sintering furnace 3. The binder of the molded body 1 is decomposed or burned. After debinding, the air is discharged from the flow path 9 and the inert gas is fed into the sintering furnace 3 by operating the three-way valve 5 so that the flow paths 7 and 8 are connected. If the inside of the sintering furnace 3 is an inert gas atmosphere, the temperature in the furnace is further increased by the heater 4 to sinter the molded body 1.

  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. Moreover, it is preferable that the temperature which performs a binder removal is 200-700 degreeC.

If the oxygen concentration is too high during sintering, Bi in Bi ₁₂ MO ₂₀ is oxidized from Bi ³⁺ → Bi ⁵⁺ and crystal defects occur in Bi ₁₂ MO ₂₀ , which constitutes a radiation imaging panel. When the photoconductive layer is used, the movement of carriers such as photoelectrons and photoholes is hindered and the sensitivity is lowered. On the other hand, even if the oxygen concentration is too low, Bi in Bi ₁₂ MO ₂₀ is reduced to Bi ³⁺ → Bi to produce crystal defects in Bi ₁₂ MO ₂₀ , which is used as a photoconductive layer constituting the radiation imaging panel. In this case, the movement of carriers such as photoelectrons and photoholes is hindered and the sensitivity is lowered. In the manufacturing method of the photoconductive layer formed of Bi ₁₂ MO ₂₀ sintered body of the present invention, inhibiting the oxidation of Bi ³⁺ → Bi ⁵⁺ by performing sintering of the Bi ₁₂ MO ₂₀ sintered body in an inert gas atmosphere Bi ³⁺ → Bi reduction can be suppressed, and a Bi ₁₂ MO ₂₀ sintered body with few crystal defects can be manufactured. Therefore, a highly sensitive photoconductive layer can be produced. Can be obtained.

In particular, when the oxygen partial pressure in the inert gas is in the range of 1 × 10 ⁻⁵ Pa to 20 Pa, it is possible to effectively suppress the oxidation of Bi ³⁺ → Bi ⁵⁺ and the reduction of Bi ³⁺ → Bi. And a highly sensitive photoconductive layer (sintered body) can be obtained.

A second method for producing a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered body, which constitutes a radiation imaging panel that records the radiation image information of the present invention as an electrostatic latent image, is a method of firing a Bi ₁₂ MO ₂₀ sintered body. The crystallization is performed in an atmosphere where the sintering temperature is 800 ° C. to 900 ° C. and the oxygen partial pressure P _O2 (Pa) is 10 ⁻³ ≦ P _O2 ≦ 10 ⁻¹ . FIG. 2 shows a schematic sectional view of an apparatus for producing the Bi ₁₂ MO ₂₀ sintered body of the present invention.

The apparatus shown in FIG. 2 includes a sintering furnace 23 having a setter 22 on which a Bi ₁₂ MO ₂₀ molded body 21 is placed, heaters 24 provided above and below the sintering furnace 23, and air in the sintering furnace 23. The flow path 28 for feeding inert gas, CO ₂ gas and CO gas, and the flow path 29 for exhausting air or inert gas in the sintering furnace 23, and sintering the flow path 28. A gas supply device for feeding air, an inert gas (Ar in this case), CO ₂ gas, and CO gas is connected to the opposite side connected to the furnace 23.

The molded body 21 is a flat molded body of the Bi ₁₂ MO ₂₀ sintered body (which becomes a photoconductive layer after being sintered), and bismuth oxide and silicon oxide or germanium oxide. Alternatively, after mixing titanium oxide powder, Bi ₁₂ MO ₂₀ powder obtained by pre-baking is formed by a forming method such as a press forming method or a doctor blade method.

The procedure for sintering the molded body will be described with reference to FIG. After the molded body 21 is placed on the setter 22, air is supplied from the flow path 28 into the sintering furnace 23, the temperature in the furnace is increased by the heater 24, the molded body 21 is dried, and the binder is evaporated. After debinding, with discharging air from the flow passage 29, Ar, open valve of the gas supply for feeding CO ₂ gas and CO gas, Ar from the channel 28 to the sintering furnace 23, CO ₂ gas and CO Supply gas. The gas supply unit is configured so that the flow rate can be controlled by a mass flow meter, and a plurality of gases are supplied into the sintering furnace 23 via a gas mixer (not shown) provided in the flow path 28. Is done.

When the inside of the sintering furnace 23 is a mixed gas atmosphere composed of Ar, CO ₂ gas and CO gas, the flow path 29 is closed, the temperature in the furnace is further increased by the heater 24, and the compact is molded at a sintering temperature of 800 ° C to 900 ° C. Sinter 21. The temperature at which the binder is removed varies depending on the type of the body to be fired, the type of the setter, the combination of the body to be fired and the setter, etc., but cannot be generally stated, but is preferably 200 to 700 ° C.

If the oxygen partial pressure is too high during sintering, Bi in Bi ₁₂ MO ₂₀ is oxidized from Bi ^{3+ to} Bi ⁵⁺ , and crystal defects are generated in Bi ₁₂ MO _20. When the photoconductive layer is formed, the reflectance is lowered and the sensitivity is lowered. On the other hand, even if the oxygen partial pressure is too low, Bi in Bi ₁₂ MO ₂₀ is reduced to Bi ³⁺ → Bi and crystal defects are generated in Bi ₁₂ MO ₂₀ , which is used as a photoconductivity constituting the radiation imaging panel. In the case of a layer, the sensitivity is lowered. In the method for producing a photoconductive layer comprising the Bi ₁₂ MO ₂₀ sintered body of the present invention, Bi ³⁺ → Bi is carried out in an atmosphere where the oxygen partial pressure P _O2 is 10 ⁻⁸ ≦ P _O2 ≦ 10 ^−6. It becomes possible to suppress the oxidation of ⁵⁺ and to suppress the reduction of Bi ³⁺ → Bi, and it is possible to produce a Bi ₁₂ MO ₂₀ sintered body with few crystal defects.

Further, the sintering is performed in an atmosphere in which the ratio of the carbon monoxide partial pressure _PCO and the carbon dioxide partial pressure _PCO2 is 10 ⁻⁶ ≦ _PCO / _PCO2 ≦ 10 ⁻⁴ , whereby CO + ½O ₂ → The oxygen partial pressure can be easily controlled by the reaction of CO ₂ . For this reason, it becomes possible to further suppress the oxidation of Bi ³⁺ → Bi ⁵⁺ , and a Bi ₁₂ MO ₂₀ sintered body with few crystal defects can be manufactured.

Subsequently, a radiation imaging panel manufactured using the Bi ₁₂ MO ₂₀ sintered body obtained by the first and second manufacturing methods of the present invention will be described. 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 manufactured by the manufacturing method of the present invention is 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 manufactured by the manufacturing method of the present invention can be read by a radiation image detector using a semiconductor material that generates a charge when irradiated with light. Can be used for a method (hereinafter referred to as TFT method) in which the accumulated charge is 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 manufactured by the manufacturing method of the present invention.

  The radiation imaging panel 10 includes a first conductive layer 11 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 transmitted through the conductive layer 11. It acts as an insulator for the charge (latent image polar charge; for example, negative charge) charged on the conductive layer 12 and the conductive layer 11, and has a charge opposite to the charge (transport polar charge; in the above example) For the positive charge), the charge transport layer 13 that acts as a substantially conductive material, the read photoconductive layer 14 that exhibits conductivity when irradiated with the read light L2 for reading described later, and the read light L2. The second conductive layer 15 having transparency is laminated in this order.

  Here, as the conductive layers 11 and 15, for example, a transparent glass plate coated with a conductive substance uniformly (nesa film or the like) is suitable. As the charge transport layer 13, the larger the difference between the mobility of the negative charge charged in the conductive layer 11 and the mobility of the positive charge having the opposite polarity, the better, the 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 13 and the reading photoconductive layer 14 is reduced, so The signal extraction efficiency can be increased.

  The reading photoconductive layer 14 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.

As the recording radiation conductive layer 12, a photoconductive layer made of a Bi ₁₂ MO ₂₀ sintered film produced by the production method of the present invention is used. That is, the photoconductive layer produced by the production method 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 10 (integrated electrostatic latent image recording device and electrostatic latent image reading device). This recording / reading system comprises a radiation imaging panel 10, 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 10, 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 10, the current detection means 70, and the connection means S 2.

  The conductive layer 11 of the radiation imaging panel 10 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 15 of the radiation imaging panel 10, the positive electrode of the power supply 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 9 is disposed on the upper surface of the conductive layer 11, and the subject 9 has a portion 9a that is transparent to the radiation L1 and a blocking portion (light-shielding portion) 9b that is not transparent. The recording irradiation means 90 uniformly exposes the radiation L1 to the subject 9, and the reading exposure means 92 scans and exposes the reading light L2 such as infrared laser light, LED or EL 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 11 and the conductive layer 15. Then, a negative charge is applied to the conductive layer 11 and a positive charge is applied to the conductive layer 15 from the power supply 50 (see FIG. 5A). As a result, a parallel electric field is formed between the conductive layers 11 and 15 in the radiation imaging panel 10.

  Next, the radiation L1 is uniformly irradiated toward the subject 9 from the recording irradiation means 90. The radiation L1 passes through the transmission part 9a of the subject 9, and further passes through the conductive layer 11. The radiation conductive layer 12 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 if the dose of the radiation L1 transmitted through the subject 9 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 12 moves at high speed in the radiation conductive layer 12 toward the conductive layer 11, and the negative charge is charged in the conductive layer 11 at the interface between the conductive layer 11 and the radiation conductive layer 12. And disappear after charge recombination (see FIGS. 5C and 5D). On the other hand, the negative charge generated in the radiation conductive layer 12 moves in the radiation conductive layer 12 toward the charge transfer layer 13. Since the charge transfer layer 13 acts as an insulator for charges having the same polarity as the charges charged in the conductive layer 11 (in this example, negative charges), the negative charge that has moved through the radiation conductive layer 12 is radiation. It stops at the interface between the conductive layer 12 and the charge transfer layer 13 and accumulates at this interface (see FIGS. 5C and 5D). The amount of stored charge is determined by the amount of negative charge generated in the radiation conductive layer 12, that is, the dose of radiation L1 transmitted through the subject 9.

  On the other hand, since the radiation L1 does not pass through the light shielding part 9b of the subject 9, no change occurs in the portion corresponding to the lower part of the light shielding part 9b of the radiation imaging panel 10 (see FIGS. 5B to 5D). In this way, by exposing the subject 9 to the radiation L1, charges corresponding to the subject image can be accumulated at the interface between the radiation conductive layer 12 and the charge transfer layer 13. 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 11 and 15 of the radiation imaging panel 10 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 15 side of the radiation imaging panel 10 by the reading exposure unit 92, the reading light L2 passes through the conductive layer 15, and the photoconductive layer 14 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 12 is irradiated with the radiation L1 to generate positive and negative charge pairs, and similarly, the radiation conductive layer 12 is irradiated with the reading light L2 to generate positive and negative charge pairs. (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 13 acts as a conductor for the positive charge, the positive charge generated in the photoconductive layer 14 moves rapidly in the charge transport layer 13 so as to be attracted to the accumulated charge, Charges recombine with the accumulated charges at the interface between the radiation conductive layer 12 and the charge transport layer 13 and disappear (see FIG. 6C). On the other hand, the negative charge generated in the photoconductive layer 14 is recombined with the positive charge of the conductive layer 15 and disappears (see FIG. 6C). The photoconductive layer 14 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 12 and the charge transport layer 13, that is, the electrostatic latent image is all charge recombined. Will be extinguished. Thus, the disappearance of the charges accumulated in the radiation imaging panel 10 means that the current I has flowed through the radiation imaging panel 10 due to the movement of charges, and this state is the radiation imaging panel 10. 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 10 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 manufactured by the manufacturing method 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 of the present invention, 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.

  The first manufacturing method of the photoconductive layer constituting the radiation imaging panel of the present invention is shown in Example I, and the second manufacturing method is shown in Example II.

[Example I]
Example 1
Bismuth oxide (Bi ₂ O ₃ ) powder and titanium oxide (TiO ₂ ) powder were blended in a molar ratio of 6: 1 and ball mill mixed in ethanol using zirconium oxide balls. This was recovered and dried, and then calcined at 800 ° C. for 8 hours to obtain Bi ₁₂ TiO ₂₀ powder by a solid phase reaction between bismuth oxide and titanium oxide. This Bi ₁₂ TiO ₂₀ powder was roughly pulverized in a mortar to a particle size of 150 μm or less, and then pulverized and dispersed in ethanol using a zirconium oxide ball in ethanol. At this time, 0.4 wt% polyvinyl butyral (PVB) was added as a dispersant for promoting dispersion. Subsequently, 3.7 wt% PVB as a binder and 0.8 wt% dioctyl phthalate as a plasticizer were added, and then pulverized and dispersed with a ball mill to prepare a slurry for sheet molding. The recovered slurry was defoamed and concentrated by vacuum defoaming to adjust the viscosity to 60 poise.

The slurry whose viscosity was adjusted was applied 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 molded body was placed on a setter (sapphire) in a tubular sintering furnace (EPKR-18K manufactured by Koyo Thermo Co., Ltd.) using a quartz tube, and the binder was removed at 470 ° C. in the atmosphere. Subsequently, sintering was performed at a sintering temperature of 800 ° C. in a nitrogen atmosphere in which nitrogen was fed at 500 cc / min (the oxygen partial pressure was 10 Pa at this time) to obtain a Bi ₁₂ TiO ₂₀ sintered body. The oxygen partial pressure in the furnace was measured by installing a zirconia oxygen concentration meter.

(Example 2)
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 1 except that sintering was performed under an argon atmosphere (500 cc / min flow) (the oxygen partial pressure at this time was 10 Pa).

(Example 3)
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 1 except that sintering was performed under a helium atmosphere (500 cc / min flow) (the oxygen partial pressure at this time was 10 Pa).

Example 4
A Bi ₁₂ SiO ₂₀ sintered body was obtained in the same manner as in Example 1 except that SiO ₂ powder was used instead of the raw material TiO ₂ powder.

(Example 5)
A Bi ₁₂ SiO ₂₀ sintered body was obtained in the same manner as in Example 2 except that SiO ₂ powder was used instead of the raw material TiO ₂ powder.

(Example 6)
A Bi ₁₂ GeO ₂₀ sintered body was obtained in the same manner as in Example 1 except that GeO ₂ powder was used instead of the raw material TiO ₂ powder.

(Example 7)
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 1, except that a BOX type electric furnace (manufactured by Koyo Thermo: UBF-VP) using a metal muffle as the sintering furnace in Example 1 was used. . The oxygen partial pressure was 5 × 10 ⁻³ Pa.

(Example 8)
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 7 except that 10 ppm oxygen mixed argon gas was used. The oxygen partial pressure was 0.3 Pa.

Example 9
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 7 except that 100 ppm oxygen mixed argon gas was used. The oxygen partial pressure was 5 Pa.

(Example 10)
A Bi ₁₂ SiO ₂₀ sintered body was obtained in the same manner as in Example 7 except that the raw material TiO ₂ was changed to SiO ₂ . The oxygen partial pressure was 5 × 10 ⁻³ Pa.

(Example 11)
A Bi ₁₂ GeO ₂₀ sintered body was obtained in the same manner as in Example 7 except that the raw material TiO ₂ was changed to GeO ₂ . The oxygen partial pressure was 5 × 10 ⁻³ Pa.

(Comparative Example 1)
A Bi ₁₂ TiO ₂₀ sintered body was obtained in the same manner as in Example 1 except that sintering was performed in the atmosphere (500 cc / min flow, oxygen partial pressure was 2 × 10 ⁴ Pa).

(Comparative Example 2)
A Bi ₁₂ SiO ₂₀ sintered body was obtained in the same manner as in Example 4 except that sintering was performed in the atmosphere (500 cc / min flow, oxygen partial pressure 2 × 10 ⁴ Pa).

(Comparative Example 3)
A Bi ₁₂ GeO ₂₀ sintered body was obtained in the same manner as in Example 6 except that the sintering was performed in the atmosphere (500 cc / min flow, oxygen partial pressure 2 × 10 ⁴ Pa).

  The sintered bodies obtained in Examples 1 to 11 and Comparative Examples 1 to 3 were bonded to an Al substrate using a conductive paste dotite manufactured by Fujikura Kasei, and gold was sputtered to a thickness of 60 nm as an upper electrode. This is a pulse generated under the condition that X-ray photocurrent signal is irradiated at a voltage of 80kV, 10mR of X-ray is irradiated for 0.1 seconds, and voltage is applied (applied voltage is equivalent to an electric field of 2.5V / μm). The above photocurrent was converted to voltage with a current amplifier and measured with a digital oscilloscope. From the obtained current / time curve, integration was performed in the range of the X-ray irradiation time, and the sensitivity was measured as the amount of generated charge.

Table 1 summarizes Examples 1 to 11 and Comparative Examples 1 to 3, and the sensitivity of each sintered body. As for sensitivity, Examples 1 to 3 are relative values of Comparative Example 1, Examples 4 and 5 are relative values of Comparative Example 2, Example 6 is relative value of Comparative Example 3, and Examples 7 to 9 are comparative. As relative values of Example 1, Example 10 was expressed as a relative value of Comparative Example 2, and Example 11 was expressed as a relative value of Comparative Example 3.

As is apparent from Table 1, Bi ₁₂ MO that can obtain 2 to 9 times higher sensitivity when sintering is performed in an inert gas atmosphere than when sintering is performed in the air. ₂₀ sintered bodies could be obtained. In Examples 7 to 11 using a sintering furnace using a muffle furnace, the oxygen partial pressure can be lowered to 5 × 10 ⁻³ Pa, and the sensitivity is remarkably increased.

As described above, the first method for producing a Bi ₁₂ MO ₂₀ sintered body of the present invention performs sintering in a conventional atmosphere because the Bi ₁₂ MO ₂₀ sintered body is sintered in an inert gas atmosphere. As compared with the Bi ₁₂ MO ₂₀ sintered body obtained by the above, there are few crystal defects. Therefore, by using this for the photoconductive layer, a highly sensitive radiation imaging panel can be obtained.

Example II
(Preparation of Bi ₁₂ SiO ₂₀ sintered body)
A bismuth oxide (Bi ₂ O ₃ ) powder and a silicon oxide (SiO ₂ ) powder are mixed at a molar ratio of 6: 1, pulverized and mixed using a ball mill, and then filled into a platinum crucible. In a mullle furnace at 800 ° C. for 8 hours. It was confirmed that the powder obtained by powder X-ray analysis was Bi ₁₂ SiO ₂₀ powder. Subsequently, Bi ₁₂ SiO ₂₀ powder was pulverized in a mortar, and 80 g of pulverized Bi ₁₂ SiO ₂₀ powder, 100 ml of ethanol, 3.65 g of polyvinyl butyral and 0.7 g of trioctyl phosphate were mixed using a ball mill. A part was distilled off to obtain a viscous dispersion. This was coated on a polyethylene terephthalate sheet so as to have a dry film thickness of 600 μm to produce a green sheet for ceramic formation.

The produced green sheet was cut into a 5 cm square and placed on a setter 22 shown in FIG. 2, air was introduced, and the mixture was heated and dried at 600 ° C. for 6 hours. Thereafter, predetermined gases A to G shown in Table 2 were introduced into a sintering furnace (KTF433 manufactured by Koyo Thermo Co., Ltd.) at 200 ml / min and baked at 844 ° C. for 6 hours to obtain a Bi ₁₂ SiO ₂₀ sintered body. .

The flow rate of the plurality of gases was controlled by a mass flow meter and supplied into the sintering furnace through a gas mixer. The oxygen partial pressure in the furnace was measured by installing a zirconia-type oxygen concentration meter in the exhaust passage 29.

(Preparation of Bi ₁₂ GeO ₂₀ sintered body)
A green sheet was prepared in the same manner as in Example 1 except that germanium oxide (GeO ₂ ) powder was used instead of silicon oxide powder, and sintered at a sintering temperature of 885 ° C. in the atmospheres A and D shown in Table 1. To obtain a Bi ₁₂ GeO ₂₀ sintered body.

(Preparation of Bi ₁₂ TiO ₂₀ sintered body)
A green sheet was prepared in the same manner as in Example 1 except that titanium oxide (TiO ₂ ) powder was used instead of silicon oxide powder, and sintered at a sintering temperature of 800 ° C. in the atmosphere of A and F shown in Table 1. To obtain a Bi ₁₂ TiO ₂₀ sintered body.

Gold electrodes were attached to both surfaces of the ceramic plate-like sintered body obtained above by vapor deposition, and X-rays generated at 70 kV from a medical tungsten tube were applied for 0.1 second with a voltage of 1 kV applied thereto. The amount of charge generated by the excessive current at this time was determined, and the sensitivity was determined by dividing this amount of charge by the absorbed dose. Table 3 shows the oxygen partial pressure, the color of the sintered body obtained by firing, and the relative sensitivity. The relative sensitivity is a relative sensitivity with the sensitivity of those obtained in the atmosphere of A in each sintered body as 1.

As is apparent from Table 3, the second method for producing the Bi ₁₂ MO ₂₀ sintered body of the present invention (sample numbers 4 to 6, 9 and 11 shown in Table 3) is based on the oxygen partial pressure P _O2 (Pa). Since the firing is performed in an atmosphere where 10 ⁻³ ≦ P _O2 ≦ 10 ⁻¹ , the sensitivity is improved by about 3 to 4 times compared to the case where the firing is performed in the air. This is presumably because a Bi ₁₂ MO ₂₀ sintered body with few crystal defects could be produced.

In particular, in the above sintering, the ratio of carbon monoxide partial pressure _PCO and carbon dioxide partial pressure _PCO2 is
0.001% / 10 (10 ^-6 ) ≤ _PCO / _PCO2 ≤ 0.1% / 10 (10 ^-4 )
Therefore, it was easy to control the oxygen partial pressure by the reaction of 2CO + O ₂ → CO ₂ , and a Bi ₁₂ MO ₂₀ sintered body with fewer crystal defects could be produced.

Schematic sectional view of an apparatus for producing a Bi ₁₂ MO ₂₀ sintered body by the first production method Schematic sectional view of an apparatus for producing a Bi ₁₂ MO ₂₀ sintered body by the second production method 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 Setter 3 Sintering furnace 4 Heater 5 Three-way valve
6,7,8,9 flow path
21 To-be-fired body (molded body)
22 Setter
23 Sintering furnace
24 heater
28,29 flow path
10 Radiation imaging panel
11 Conductive layer
12 Radiation conductive layer for recording
13 Charge transport layer
14 Photoconductive layer for recording
15 Conductive layer
70 Current detection means

Claims (6)

A photoconductive layer composed of a Bi ₁₂ MO ₂₀ sintered body (wherein M is at least one of Ge, Si, and Ti) constituting a radiation imaging panel that records radiation image information as an electrostatic latent image. A method for producing a photoconductive layer, characterized in that the Bi ₁₂ MO ₂₀ sintered body is sintered in an inert gas atmosphere.   The method for producing a photoconductive layer according to claim 1, wherein the inert gas is a rare gas. 3. The method for producing a photoconductive layer according to claim 1, wherein an oxygen partial pressure in the inert gas atmosphere is in a range of 1 × 10 ⁻⁵ Pa to 20 Pa. 4.   The method for producing a photoconductive layer according to claim 3, wherein the sintering is performed in a sintering furnace using a metal muffle. A photoconductive layer composed of a Bi ₁₂ MO ₂₀ sintered body (wherein M is at least one of Ge, Si, and Ti) constituting a radiation imaging panel that records radiation image information as an electrostatic latent image. In the production method, the Bi ₁₂ MO ₂₀ sintered body is sintered at a sintering temperature of 800 ° C. to 900 ° C. and an oxygen partial pressure P _O2 (Pa) of 10 ⁻³ ≦ P _O2 ≦ 10 ⁻¹ . A method for producing a photoconductive layer, which is performed in an atmosphere. Further, the ratio of carbon monoxide partial pressure _PCO and carbon dioxide partial pressure _PCO2
10 ^-6 ≦ P _CO / P _{CO 2} ≦ 10 ^-4
A method for producing a photoconductive layer, which is performed in an atmosphere as described above.

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