Patent Application
20130334431
1. Field of the Invention
The present invention relates to a detecting apparatus and a radiation detecting system.
2. Description of the Related Art
A technique of manufacturing a panel for a liquid crystal display using a thin film transistor (TFT) is being developed these days, thereby developing a large-sized panel and a large-sized screen of a display unit. This manufacturing technique is applied to a large-sized area sensor including photoelectric conversion elements constituted by a semiconductor and switching elements such as TFTs. Such an area sensor is used in a field of a radiation detecting apparatus such as a medical X-ray detecting apparatus in combination with a scintillator which converts radiation such as an X-ray into light such as visible light.
An example of the scintillator which converts radiation into visible light is a scintillator made from an alkali halide system material represented by a material in which Tl is doped on cesium iodide (hereinafter referred to as CsI). Alternatively, it is common to use a deposition layer of a granular phosphor in which a very small amount of a trivalent rare earth such as terbium or europium is doped as a luminescence center on a base material of metal oxysulfide, for example, a granular phosphor (hereinafter referred to as GOS) in which Tb is doped on Gd2O2S.
As for the area sensor, it is common to form, on a surface of the area sensor at its scintillator side, a protective layer to restrain adverse effects on the photoelectric conversion elements due to adhesion of foreign matters to the surface. In this case, parasitic capacitance markedly occurs in signal lines or the like as described later. A material of the protective layer to be used is a material durable to high temperatures caused at the time of the formation of the scintillator. For example, as an organic material having a high heat resistance, a polyimide resin and an epoxy resin can be used in particular.
For example, the polyimide resin as the organic material has a high chemical resistance and therefore is soluble only in a solvent having a polar group. Examples of the solvent having a polar group include N-methyl-2-pyrrolidone (hereinafter referred to as NMP), N,N-dimethyl formaldehyde, N,N-dimethylacetamide, cyclohexanone, cyclopentanone, and the like. Further, in a case of the epoxy resin, an organic substance having a hydroxy group as a prepolymer, such as bisphenol A, is used. Further, an organic substance or acid anhydride having an amino group is used as a curing agent, so that hydroxy groups included in a residual curing agent, a principal chain, and a side chain remain behind in the sensor protective layer. This may cause such a problem that the solvent having a polar group may remain behind in a resin layer after the protective layer has been formed.
If a polar solvent or a polar group remains behind in the protective layer, a difference in parasitic capacitance occurs between a bias line connected to the conversion element via the protective layer and a signal line for transmitting an electric signal from the conversion element, which may cause unevenness in image. In regard to this problem, U.S. 2009/0040348 A1 proposes the followings. In U.S. 2009/0040348 A1, a plurality of bias lines and a plurality of signal lines are provided alternately at predetermined intervals in an area in a protective layer. The plurality of bias lines is commonized outside the area of the protective layer by connection lines provided so as to intersect with the plurality of signal lines.
However, the method in U.S. 2009/0040348 A1 may cause a difference in parasitic capacitance between a plurality of photoelectric conversion elements due to application unevenness in the protective layer, so that unevenness in image due to the difference in parasitic capacitance may occur.
The present invention is accomplished in view of the above problems, and is able to provide a detecting apparatus and a radiation detecting system each of which is able to suppress unevenness in image due to a difference in parasitic capacitance between a plurality of photoelectric conversion elements.
A detecting apparatus according to the present invention includes a plurality of photoelectric conversion elements, a protective layer made from an organic material provided so as to cover the plurality of photoelectric conversion elements, and a conductive member provided between the plurality of photoelectric conversion elements and the protective layer so as to cover the plurality of photoelectric conversion elements and receiving a predetermined potential.
A detection system according to the present invention includes the detecting apparatus, signal processing unit for processing a signal from the detecting apparatus, storage unit for storing the signal from the signal processing unit, display unit for displaying the signal from the signal processing unit, transmission processing unit for transmitting the signal from the signal processing unit, and a radiation source for generating radiation.
According to the present invention, parasitic capacitance to occur between a plurality of photoelectric conversion elements and a protective layer is largely restrained, and a difference in parasitic capacitance between the plurality of photoelectric conversion elements is restrained. As a result, a detecting apparatus and a radiation detecting system each of which is able to restrain unevenness in image due to a difference in parasitic capacitance between a plurality of photoelectric conversion elements can be provided.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention will be described below with reference to drawings. Note that, in the present specification, radiation includes electromagnetic waves such as α-rays, β-rays, and γ-rays, other than X-rays.
Initially, a detecting apparatus is described with reference to
Next will be described a sensor substrate 100 of a detecting apparatus according to a first embodiment of the present invention with reference to
The sensor substrate 100 is a sensor panel for converting light converted from radiation by a scintillator 400 provided in an area 115, into an electric signal. As illustrated in
The photoelectric conversion element 101 converts, into an electric charge, the light converted from radiation by the scintillator 400, and materials such as amorphous silicon and polysilicon can be used therefor, for example. As illustrated in
Note that the present embodiment deals with a MIS-type photoelectric conversion element. The photoelectric conversion element 101 includes a first conductive layer 120 serving as a first electrode, an insulating layer 121, a semiconductor layer 122, an impurity semiconductor layer 123, a second conductive layer 124, and a third conductive layer 125 serving as a second electrode, which are sequentially provided in layers on the insulating substrate 119, and is covered with an insulating layer 126. Here, the second conductive layer 124 is a bias line 105, which will be described later.
A plurality of signal lines 103 is provided in one direction (a row direction), respectively connected to either ones of sources and drains of the TFTs 102 of the plurality of pixels provided in another direction (a column direction) different from the one direction, and then connected to the reading circuit 110. The signal line 103 is a wiring line for transmitting a signal based on an electric charge caused by photoelectric conversion by the photoelectric conversion element 101, to a reading circuit 110 via the TFT 102.
A plurality of driving lines 104 are provided in the another direction, respectively connected to gates of the TFTs 102 of the plurality of pixels provided in the one direction, and then connected to a driving circuit 111. When a TFT 102 is selected per row by the driving circuit 111 via the driving line 104, a signal photoelectrically converted by the photoelectric conversion element 101 is read out by the TFT 102 and is output to the reading circuit 110 via an external line 109 connected to a connecting terminal 107. Further, the other one of the source and the drain of the TFT 102 is connected to the first electrode, which is one electrode of the Photoelectric conversion element 101.
A plurality of bias lines 105 is arranged in the one direction and respectively connected to second electrodes, which are the other electrodes of the Photoelectric conversion elements 101 of the plurality of pixels provided in the another direction. The bias line 105 is a wiring line for applying a voltage (Vs) to the second electrode of the photoelectric conversion element 101 so as to cause the photoelectric conversion element 101 to perform photoelectric conversion. The bias line 105 is connected to a power supply unit (not illustrated) provided within the reading circuit 110 via a connection line 106, an external connection electrode 107, and an external line 109, which will be described later. The plurality of bias lines 105 is connected to the connection line 106 provided outside the pixel area 114 and the connection line 106 intersects with the plurality of signal lines 103.
As illustrated in
A wiring line for connecting the connecting terminal 107 and the connection line 106, and the connecting terminal 107 are constituted by the second conductive layer 124, as illustrated in
The scintillator 400 converts radiation such as an X-ray into light within a wavelength bandwidth detectable by the photoelectric conversion element 101. Examples of a material of the scintillator 400 include any scintillator materials of alkali halides and metal oxysulfides.
As the alkali halides, a material in which Tl or Na is doped on cesium iodide (hereinafter referred to as CsI:Tl, CsI:Na), a material in which Tl is doped on cesium bromide (CsBr:Tl) , and the like are used. In a case where an alkali halide material is used, the scintillator 400 can be formed by vacuum deposition of the alkali halide material on a sensor protective layer 300 formed on the sensor panel 100. During the vacuum deposition, the sensor substrate 100 is heated to 100° C. to 200° C. due to radiant heat and heating by a heater. On that account, as the sensor protective layer 300, which will be described later, it is necessary to use a material which does not change in quality at a temperature during the vacuum deposition.
As the metal oxysulfides, a granular scintillator material (e.g., Gd2O2S:Tb which is referred to as GOS) in which a very small amount of a trivalent rare earth such as terbium or europium is doped as a luminescence center on a base material of metal oxysulfide, or the like is used. In a case where a metal oxysulfide material is used, a paste obtained by dispersing the scintillator material in an organic solvent called a vehicle is prepared. The scintillator 400 can be obtained in such a manner that after the vehicle is applied on the sensor protective layer 300 by a method such as screen printing or slit coating, the organic solvent is removed by heating.
The vehicle contains an organic resin called a binder for binding metal oxysulfides and a solvent for dissolving the binder. When a blending amount of the binder is set to about 10% or less of the weight of the vehicle, it is possible to increase a filling factor of the scintillator material, thereby attaining the scintillator 400 with high luminance. As the solvent contained in the vehicle, a solvent having a low molecular weight and including a hydroxy group, such as water and an alcohol solvent, can be used in view of environmental problems these days. Accordingly, the binder is any organic resin soluble to water or an alcohol solvent, for example, resins of polyvinylacetal, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylbutyral, celluloses, and acrylics, each of which has a polar group. Further, as the binder, a polyvinylacetal resin of S-LEC KW (manufactured by Sekisui Chemical Co., Ltd.) which is soluble to water or S-LEC B series (manufactured by Sekisui Chemical Co., Ltd.) which is soluble to ethanol, and the like can be used. The scintillator 400 made by using such a scintillator material of metal oxysulfides can be adhered to the protective layer 300, which is described below, by the binder.
The protective layer 300 for restraining adverse effects on the photoelectric conversion element 101 due to adhesion of foreign substances to a surface is provided in an area 113 of the sensor substrate 100 so as to cover at least the pixel area 114. Note that in the configuration illustrated in
Note that, in the present embodiment, in order to finely pass the light converted by the scintillator 400 to the photoelectric conversion element 100, a material having optical transparency to the light (visible light or the like) converted by the scintillator 400 can be used as a material of the protective layer 300. The material of the protective layer 300 is an organic material durable to a heat treatment at the time of the formation of the scintillator, and a polyimide resin and an epoxy resin can be used in particular.
Such an organic material may cause a polar group to remain behind in at least one of a principal chain, a side chain, and a solvent in constituent materials of the sensor protective layer 300. Such a polar group
corresponds to an atom group represented by a hydroxy group (—OH) , a carbonyl group (—C═O), a carboxyl group (—COOH), a cyano group (—CN) , an amino group (—NRR′), a nitro group (—NO2), and the like. Further, at least one of a positive ion and a negative ion may be included, as a catalyst or impurities, in the solvent used to form the protective layer 300 made from an organic material. Metal ions such as Na+ and Ca2+ are often seen as the positive ion, while the negative ion encompasses Cl−, OH−, CN−, I−, and the like.
A content of the solvent having such a polar group in the sensor protective layer 300 can be set to about 5% or less, from the viewpoint that the sensor protective layer 300 is formed by drying, for example, at about 200° C. to 230° C. A conceivable method for forming the sensor protective layer 300 may be a formation method by a slit coater, a spin coater, a screen printer, vapor deposition, or CVD. In a case where the sensor protective layer is formed by application, the application is easily performed if a viscosity is 2000 mPas or less. In the meantime, in a case where the sensor protective layer is formed by a vacuum process, a lower evaporating temperature can restrain a temperature rise of the sensor substrate 100. As the polyimide resin, LP-62 manufactured by Toray Industries, Inc. can be used from the viewpoint of viscosity and transparency. As the epoxy resin, RO-7198 manufactured by Sanyu Rec Co., Ltd. or CV5133I manufactured by Panasonic Electric Works Co., Ltd can be used from the viewpoint of viscosity and transparency.
As such, when the protective layer 300 in which a polar group or a polar solvent may remain behind is provided so as to cover the plurality of photoelectric conversion elements 101 in the pixel area 114, parasitic capacitance may occur due to the polar group or the polar solvent. Further, the parasitic capacitance may vary between the plurality of photoelectric conversion elements 101 due to unevenness in thickness of the protective layer 300. This may cause unevenness in image due to a difference in the parasitic capacitance. In view of this, a conductive member 200 to cover the plurality of photoelectric conversion elements 101 is provided between the plurality of photoelectric conversion elements 101 and the protective layer 300. A predetermined constant potential is supplied to the conductive member 200, so that a potential of the conductive member 200 is fixed to the predetermined constant potential.
In the present embodiment, as illustrated in
The conductive member 200 can have optical transparency to the light (visible light) converted by the scintillator 400. Particularly, the conductive member 200 can have an optical transmittance of 70% or more in a wavelength range from 500 to 600 nm. In other words, to have optical transparency indicates that a transmittance to target light is 70% or more. Further, a specific resistance of the conductive member 200 can be set to 1×10−3 Ω·cm or less. More specifically, a transparent conductive oxide formed with a thickness of 1 μm or less, such as ITO (indium tin oxide), ZnO (zinc oxide), or indium oxide, can be used as the conductive member.
Further, as illustrated in
In the configuration illustrated in
Further, in a case where the conductive member 200 is provided, for example, on other areas as well as the pixel area 114, it is not necessary for the other areas to pass the light converted by the scintillator 400 therethrough. In view of this, it is not necessary to use a conductive material having transparency for that part of the conductive member 200 which is placed on the other areas except the pixel area 114. For such a part, metals such as Al, Cu, Au, and Ag having a high conductivity and having an optical transparency lower than that of ITO and the like can also be used, thereby resulting in that the use of expensive rare metal such as indium can be restrained in consideration of environmental conservation and manufacturing cost. More specifically, as illustrated in
In either case, the scintillator 400 can be provided in an area 115 having a peripheral portion placed between the peripheral portion of the pixel area 114 and the peripheral portion of the area 113. A method for supplying a predetermined potential to the conductive member 200 is as follows: As illustrated in
Here, when the conductive member 200 has the same potential as the bias lines 105 (or the signal lines 103), a potential difference with respect to each line can be eliminated, thereby restraining parasitic capacitance. In this case, the power supply unit supplies a potential to the conductive member 200 so that the potential is equivalent to that of the bias lines 105 (or the signal lines 103). Particularly, since the bias lines 105 are close to the conductive member 200, when the conductive member 200 has the same potential as the bias lines 105, a large parasitic-capacitance reduction effect can be yielded. Note that in a case where the conductive member 200 is controlled to have the same potential as the signal lines 103, the conductive member 200 may be electrically divided into pieces corresponding to respective signal lines 103 in a stripe-like manner, so that a potential can be controlled independently per divided conductive member.
With this configuration, respective stripe-like conductive members corresponding to the respective signal lines 103 can individually be controlled so as to have the same potentials as the respective signal lines 103, thereby parasitic capacitance can be more surely restrained. In this case, it is conceivable that an I TO thin film or the like, for example, corresponding to the conductive member 200 is deposited, and then the ITO thin film is divided into respective conductive members by lithography and dry-etching.
Next will be described a structure of a radiation detecting apparatus, which is a detecting apparatus according to a second embodiment, with reference to
The binder is an organic resin. In recent years, organic resins soluble to water or alcohol such as ethanol have been often used from the viewpoint of environmental protection, but these resins often include a polar group. On that account, direct application of such resins onto a sensor sometimes causes unevenness in image.
In the present embodiment, the binder 510 adheres to the conductive member 200, and the conductive member 200 exists between a plurality of photoelectric conversion elements 101 and the scintillator 400. The plurality of Photoelectric conversion elements 101 is hereby electrically shielded by the conductive member 200, thereby the scintillator 400 including the binder 510 having polarity can be provided at a given position on the conductive member 200. As such, even if an organic material having a polar group, such as the binder 510, is provided on each wiring line or the pixel area 114, variation in parasitic capacitance is restrained by effects of the conductive member 200, so that unevenness in image can be restrained.
The present embodiment discloses a radiation detecting system in which the detecting apparatus selected from the first and second embodiments is applied to an X-ray diagnosis system.
In this radiation detecting system, an X-ray 6060 generated by an X-ray tube 6050, which is a radiation source, passes through a chest 6062 of a patient (or an examinee) 6061 and is incident on a radiation detecting apparatus (an image sensor) 6040. This radiation detecting apparatus 6040 is selected from the first and second embodiments. The X-ray thus incident thereon includes information about an inside of a body of the patient 6061. A scintillator emits light in response to the incidence of the X-ray, and photoelectric conversion elements of a sensor substrate photoelectrically convert this light, so that an electric signal is obtained. This information is converted into a digital signal and subjected to an image process by an image processor 6070 serving as signal processing unit, so that the information can be observed by a display 6080 serving as displaying unit in a control room.
Further, this information can be transmitted to a distant place by transmission processing unit (a telephone line 6090 in the example in the figure) such as networks including a telephone line, LAN, the Internet, and the like. The information thus transmitted is able to be displayed on a display 6081 serving as display unit in a doctor room or the like located at a different place, or to be stored in storage unit such as an optical disk. This allows a doctor at a distant place to make a diagnosis. Further, the information can be stored in a film 6110 by a film processor 6100 serving as storage unit.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-138074 filed on Jun. 19, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-138074 | Jun 2012 | JP | national |
