PHOTOELECTRIC CONVERSION SUBSTRATE, RADIATION DETECTOR, AND RADIOGRAPHIC IMAGE CAPTURE DEVICE

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese Patent Application No. 2011-185236 filed on Aug. 26, 2011, and Japanese Patent Application No. 2012-165136 filed on Jul. 25, 2012, the disclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photoelectric conversion substrate, a radiation detector, and a radiographic image capture device, and in particular relates to a photoelectric conversion substrate, a radiation detector and a radiographic image capture device employed in such applications as radiographic image capture.

2. Description of the Related Art

Radiographic image capture devices for capturing radiographic images are known in which a radiation detector detects radiation that has been irradiated from a radiation irradiation device and has passed through a subject. As the radiation detector of such a radiographic image capture device, detectors are known that are provided with a scintillator such as a fluorescent body that converts irradiated radiation into light, and a photoelectric conversion substrate configured with pixels, each pixel provided with a photoelectric conversion element that generates charge by being illuminated with light converted by the scintillator, and a switching element that reads the charge generated in the photoelectric conversion element.

Since such radiation detectors are provided with a scintillator above the photoelectric conversion substrate, technology is known for improving the adhesion between the photoelectric conversion substrate and the scintillator.

For example, technology is described in Japanese Patent Application Laid-Open (JP-A) No. 2001-74846 for making it more difficult to separate a protection layer for protecting the photoelectric conversion elements and a scintillator from each other by interposing between the protection layer and the scintillator a metallic layer or a metallic compound layer as a separation prevention layer having high thermal conductivity and strong bonding force to the scintillator.

However, in radiation detectors, electrodes and wiring lines of switching elements also become unstable in a case in which an electric potential becomes unstable due to being affected by such influences as external magnetic noise or internal static electricity, and electrical distortion and disruption may occur in radiographic images. Technology is accordingly known for stabilizing electric potentials.

For example, technology is described in JP-A No. 2004-226313 in which a wavelength conversion body and conduction layer are disposed in a radiation detection device above a photoelectric conversion panel formed with photoelectric conversion elements, and the conduction layer is connected to a fixed voltage through a fixed voltage line of the photoelectric conversion panel.

However, charge that builds up on the surface of the photoelectric conversion element in a case in which surface treatment is performed on the surface of such a photoelectric conversion substrate may cause electrostatic destruction of the photoelectric conversion element. For example, the presence of air when plasma processing is performed at atmospheric pressure as surface treatment makes static buildup less likely to occur, and the risk of causing electrostatic destruction is accordingly low. However, there is a high risk of triggering electrostatic destruction when plasma processing is performed in a vacuum.

Electrostatic destruction may also be triggered when static buildup occurs on the surface of the photoelectric conversion substrate, not only when performing surface treatment.

There is also the possibility of a deterioration of the image quality of radiographic images due to charge accumulating in a condenser formed by a sensor portion and a metal-containing film, such as an antistatic film, provided on the surface of the photoelectric conversion substrate.

Electrostatic destruction of the sensor portions may be triggered and/or deterioration in radiographic image quality may be induced by the electric potential of the antistatic film formed on the surface of the photoelectric conversion substrate.

SUMMARY

The present invention provides a photoelectric conversion substrate, a radiation detector, and a radiographic image capture device that can prevent electrostatic destruction of photoelectric conversion elements, and can set a first conducting member to a given voltage.

A first aspect of the present invention is a photoelectric conversion substrate including a substrate, plural pixels, a flattening layer and a first conducting member. The plural pixels are each provided with a sensor portion and a switching element that are formed on the substrate. The sensor portion includes a photoelectric conversion element that generates charge according to illuminated light, and the switching element reads out the charge from the sensor portion. The flattening layer flattens the surface of the substrate having the switching elements and the sensor portions formed thereon. The first conducting member is formed over the whole face of the flattening layer and is configured such that a voltage applied to the first conducting member may be selected to be a predetermined voltage.

The above aspect may be configured such that the predetermined voltage is a voltage selected from the group consisting of a ground voltage, a bias voltage that is applied to the photoelectric conversion elements, and a voltage of a power source that is supplied to the photoelectric conversion substrate.

The above aspect may be configured such that the voltage applied to the first conducting member is selected according to a predetermined condition.

The above aspect may be configured such that selection is made so as to apply a bias voltage that is applied to the photoelectric conversion elements to the first conducting member in a case in which radiographic image capture using the photoelectric conversion substrate.

The above aspect may be configured such that the predetermined voltage includes a ground voltage of a frame of a casing in which the photoelectric conversion substrate is housed.

The above aspect may be configured such that the first conducting member absorbs a predetermined long wavelength component of the illuminated light.

Generally, long wavelength components are not so readily refracted as short wavelength components, and so long wavelength components of oblique light have a higher probability of being incident on an adjacent pixel. Oblique light that is incident on adjacent pixels in this manner may cause blurring in radiographic images. The present exemplary embodiment addresses this issue by absorbing predetermined long wavelength components (for example, red light) of illuminated light with the first conducting member, enabling the long wavelength components to be suppressed from being incident onto adjacent pixels.

The above aspect may be configured such that the photoelectric conversion elements are organic photoelectric conversion elements formed with quinacridone.

The above aspect may be configured such that the first conducting member has transparency to light.

The above aspect may be configured further including a selection section that selects the predetermined voltage as the voltage to be applied to the first conducting member of the photoelectric conversion substrate.

The above aspect may be configured further including a second conducting member that is formed on a side of the substrate opposite to a side on which the sensor portion and the switching element are formed, wherein the voltage applied to the second conducting member is selected to be the predetermined voltage.

The above aspect may be configured such that the second conducting member is electrically connected to the first conducting member.

The above aspect may be configured such that the selection section is connected to ground and to a voltage source other than ground, and the selection section selects the predetermined voltage from the ground voltage or a voltage supplied from the voltage source as the voltage to be applied to the first conducting member.

A second aspect of the present invention is a radiation detector including the photoelectric conversion substrate of the first aspect, and a light emitting layer that is disposed on the first conducting member of the photoelectric conversion substrate and that emits light according to a radiation amount of irradiated radiation.

The above aspect may be configured further including a controller that selects a voltage applied to the first conducting member of the photoelectric conversion substrate according to a predetermined condition.

The above aspect may be configured further comprising a reflection layer formed on the light emitting layer, the reflection layer reflecting light emitted from the light emitting layer, wherein a voltage applied to the reflection layer is selected to be the predetermined voltage.

The above aspect may be configured such that the reflection layer is electrically connected to the first conducting member.

The above aspect may be configured such that the light emitting layer is formed with columnar crystals of an alkali halide.

The above aspect may be configured such that the selection section is connected to ground and to a voltage source other than ground, and the selection section selects the predetermined voltage from the ground voltage or a voltage supplied from the voltage source other than the ground as the voltage to be applied to the first conducting member.

A third aspect of the present invention is a radiographic image capture device including the radiation detector of the second aspect, and an image capture section that reads the charge that has been generated in the radiation detector according to the irradiated radiation and captures a radiographic image.

The above aspect may be configured such that the selection section is connected to ground and to a voltage source other than ground, and the selection section selects the predetermined voltage from the ground voltage or the voltage source as the voltage to be applied to the first conducting member.

The aspects of the present invention can accordingly prevent electrostatic destruction of the photoelectric conversion elements and also can set the first conducting member to a given voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a diagram illustrating an example of an overall configuration of a radiographic image capture device according to the present exemplary embodiment;

FIG. 2 is a schematic configuration diagram illustrating an example of a scintillator according to the present exemplary embodiment;

FIG. 3 is a plan view illustrating an example of a configuration of a single pixel unit of a radiation detector on a photoelectric conversion substrate of the present exemplary embodiment;

FIG. 4 is a cross-section of the radiation detector illustrated in FIG. 3, taken along line A-A;

FIG. 5 is a cross-section of the radiation detector illustrated in FIG. 3, taken along line B-B;

FIG. 6 is a graph illustrating the light emission property of CsI(Tl) and the absorption wavelength range of quinacridone;

FIG. 7 is an explanatory drawing related to short wavelength components incident to a radiation detector according to the present exemplary embodiment;

FIG. 8 is an explanatory drawing related to long wavelength components incident to a radiation detector according to the present exemplary embodiment;

FIG. 9 is a graph illustrating the refractive index of ITO;

FIG. 10 is diagram illustrating an example of a configuration of a selection section according to the present exemplary embodiment;

FIG. 11 is an explanatory diagram (cross-section) explaining a fabrication process of a radiation detector according to the present exemplary embodiment;

FIG. 12 is an explanatory drawing (cross-section) explaining a process following the process illustrated in FIG. 11 in the fabrication processes of a radiation detector according to the present exemplary embodiment; and

FIG. 13 is a cross-section illustrating an example of a radiation detector formed with a conducting layer and a reflecting layer according to another exemplary embodiment.

DETAILED DESCRIPTION

Outline explanation is given of a radiographic image capture device employing a radiation detector provided with a photoelectric conversion substrate of the present exemplary embodiment. FIG. 1 is a drawing illustrating an example of an overall configuration of a radiographic image capture device employing a radiation detector provided with a photoelectric conversion substrate of the present exemplary embodiment. Note that illustration of a scintillator 70 (described in detail later) has been omitted from in FIG. 1.

A radiographic image capture device 100 according to the present exemplary embodiment is provided with an indirect-conversion method radiation detector 10, a scan signal control device 104, signal detection circuits 105, a controller 106, and a bias power source 110. The radiation detector 10 of the present exemplary embodiment is provided with a photoelectric conversion substrate 60 and a scintillator 70.

Explanation is first given regarding the scintillator 70. An example of an outline configuration of the scintillator 70 of the present exemplary embodiment is illustrated in FIG. 2. The scintillator 70 converts irradiated radiation into light, and emits the light. Namely, the scintillator 70 of the present exemplary embodiment emits light according to the amount of irradiated radiation.

The scintillator 70 may for example employ crystals formed from CsI(Tl), GOS (Gd₂O₂S:Tb), NaI:Tl (thallium-activated sodium iodide), CsI:Na (sodium-activated cesium iodide), however the scintillator 70 is not limited to one formed from these materials. Note that out of these materials, it is preferable to employ CsI(Tl) from the perspective of being a material having light emission spectrum matching the maximum spectral sensitivity value of an a-Si photodiode (in the region of 550 nm) and being a material not liable to degrade from moisture over time.

It is also preferable for the wavelength region of light emitted by the scintillator 70 to be in the visible light region (wavelengths of 360 nm to 830 nm), and it is even more preferable to be in a wavelength region including green wavelength range (495 nm to 570 nm) in order to allow monochrome image capture by the radiographic image capture device 10.

As a specific fluorescent body employed in the scintillator 70, a fluorescent body including cesium iodide (CsI) is preferably employed in a case in which X-rays are employed as radiation for image capture, and it is particularly preferable, for example, to employ CsI(Tl) with a light emitting spectrum of 400 nm to 700 nm when being irradiated by X-ray. Note that there is the emission peak wavelength of CsI(Tl) in the visible light region at 565 nm.

From the perspective of light emission efficiency the scintillator 70 may be configured from columnar crystals, and in particular alkali halide columnar crystals. As a specific example, in the present exemplary embodiment, the scintillator 70 employed is configured with CsI(Tl) columnar crystals. The scintillator 70 of the present exemplary embodiment illustrated in FIG. 2 is configured from a non-columnar portion 71 formed from non-columnar CsI(Tl) crystals, and a columnar portion 72 formed from columnar crystals. Note that the non-columnar portion 71 side of the scintillator 70 is in contact with the photoelectric conversion substrate 60 side (see FIG. 4 and FIG. 5).

Light is generated in each columnar crystal in the columnar portion 72 so as to obtain efficient light emission. The gaps between the columnar crystals also act as light guides and suppress blurring of radiographic images by suppressing light diffusion. Light that has penetrated into the deep portion of the scintillator 70 is reflected by the non-columnar portion 71 formed from non-columnar crystals, thereby improving the detection efficiency of emitted light, and improving the adhesion of the scintillator 70 to the photoelectric conversion substrate 60.

As shown in FIG. 2, if the thickness of the columnar portion 72 of the scintillator 70 is denoted t1, and the thickness of the non-columnar portion 71 is denoted t2, then the relationship of t1 and t2 can be made to satisfy the Formula (I) below.

0.01≦(t2/t1)≦0.25 Formula (I)

By setting the thickness t1 of the columnar portion 72 and the thickness t2 of the non-columnar portion 71 so as to satisfy Formula (I), the light emission efficiency along thickness direction of the scintillator 70, light diffusion prevention and the region of light reflection fall in a preferable region, and light emitting efficiency, light detection efficiency and image resolution are further improved. If the thickness t2 of the non-columnar portion 71 is too thick, the region of poor light emission efficiency increases, leading to concerns regarding decreased sensitivity. It is more preferable for (t2/t1) to be in a range of 0.02 to 0.1 from such a perspective.

From the perspective of achieving efficient reflection, the crystal size of the non-columnar crystals in the non-columnar portion 71 is preferably 0.2 μm to 7.0 μm, and more preferably 1.0 μm to 6.0 μm. From the perspective of achieving efficient reflection, the shape of the non-columnar crystals may be a substantially spherical shape, and the non-columnar portion 71 may be configured as an aggregate body of near-spherical crystals (substantially spherical crystals).

Explanation follows of the photoelectric conversion substrate 60 of the present exemplary embodiment. As shown in FIG. 1, the radiation detector 10 of the present exemplary embodiment is provided with pixels 20 (a pixel region 20A), a selection section 54, and an internal power source 56. Plural of the pixels 20 are disposed in a two-dimensional formation (matrix formation) in the photoelectric conversion substrate 60 of the present exemplary embodiment. Each of the pixels 20 includes: a sensor portion 103, provided with an upper electrode, a semiconductor layer and a lower electrode, described later, receiving light that has been converted by the scintillator 70 from irradiated radiation, and accumulating charge, and a TFT switch 4 that reads charge accumulated in the sensor portion 103.

Plural of the pixels 20 are disposed in a matrix formation along one direction (the direction along scan lines 101 in FIG. 1) and a direction intersecting with the direction along scan lines 101 (the direction along signal lines 3 in FIG. 1). The array of the pixels 20 is simplified in the illustration of FIG. 1. In reality there are, for example, 1024×1024 individual pixels 20 disposed along the direction along scan lines 101 and along the direction along signal lines 3. The region of the photoelectric conversion substrate 60 formed with the pixels 20 is referred to below as the pixel region 20A.

Plural scan lines 101 and plural signal lines 3 are disposed on the photoelectric conversion substrate 60 so as to intersect with each other. The scan lines 101 switch the TFT switches 40N or OFF. The signal lines 3 read charge accumulated in the sensor portions 103.

An electrical signal, corresponding to the amount of accumulated charge in the sensor portion 103, flows in each of the signal lines 3 by switching ON the TFT switch 4 in any of the pixels 20 connected to this signal line 3. A signal detection circuit 105 is connected to each of the signal lines 3 for detecting the electrical signal flowing out from each of the signal lines 3. A scan signal control device 104 is also connected to the scan lines 101 for outputting a scan signal to each of the scan lines 101 for ON/OFF switching of the TFT switches 4.

The signal detection circuits 105 are each inbuilt with an amplifier circuit (not shown in the drawings) for each of the respective signal lines 3, and the amplifier circuits amplify input electrical signals. Electrical signals input by each of the signal lines 3 are amplified by the amplifier circuits and detected in the signal detection circuit 105. The signal detection circuits 105 thereby detect the charge amount that has been accumulated in each of the sensor portions 103 as data for each pixel 20 configuring a radiographic image. Note that “detection” of the electrical signals refers here to sampling the electrical signals.

The controller 106 is connected to the signal detection circuits 105 and the scan signal control circuit 104. The controller 106 executes specific processing on the electrical signals detected by the signal detection circuits 105. The controller 106 also outputs a control signal expressing the timing of signal detection to the signal detection circuits 105, and outputs a control signal expressing the timing for scan signal output to the scan signal control device 104.

Common electrode lines 25 are provided to the photoelectric conversion substrate 60 for applying a bias voltage to the sensor portions 103 of the pixels 20. The common electrode lines 25 are connected to the bias power source 110.

The photoelectric conversion substrate 60 of the present exemplary embodiment is further provided with the selection section 54 and an internal power source 56. The internal power source 56 supplies a power source voltage through power source voltage lines, not shown in the drawings, to each of the circuits on the photoelectric conversion substrate 60. The selection section 54 performs switching (described in detail later) in response to control signals input from the controller 106, so as to connect the connection destination of a connection line 52 connected to a conduction film 30 to one destination selected from the bias power source 110 (the common electrode lines 25), the internal power source 56 (a power source supply line 57) and a ground line 59 (the frame ground of a housing 80: FGND).

Note that the radiographic image capture device 100 of the present exemplary embodiment is housed inside the housing 80. The housing 80 is connected to an external ground, and forms a frame ground.

More detailed explanation now follows regarding the photoelectric conversion substrate 60 according to the present exemplary embodiment, with reference to FIG. 3 to FIG. 5. Note that FIG. 3 shows a plan view illustrating a structure of a single pixel unit of a radiation detector on the photoelectric conversion substrate 60 according to the present exemplary embodiment. FIG. 4 shows a cross-section taken along the line A-A of FIG. 3 (shows a cross-section taken along the bent line A-A as stretched out into a flat plane). FIG. 5 shows a cross-section taken along the line B-B of FIG. 3. Note also that the selection section 54 and the connection line 52 have been omitted from illustration in FIG. 3 to FIG. 5.

As shown in FIG. 4 and FIG. 5, the radiation detector 10 of the present exemplary embodiment is formed with an insulating substrate 1 configured from a material such as non-alkali glass, on which the scan lines 101, and gate electrodes 2 are formed. The scan lines 101 and the gate electrodes 2 are connected together (see FIG. 3). The wiring layer in which the scan lines 101 and the gate electrodes 2 are formed (this wiring layer is referred to below as “the first signal wiring layer”) is formed from Al or Cu, or a layered film mainly composed of Al or Cu. However, the material of the first signal wiring layer is not limited thereto.

An insulation film 15 is formed on the scan lines 101 and the gate electrodes 2 on one face so as to cover the scan lines 101 and the gate electrodes 2. The locations of the insulation film 15 positioned over the gate electrodes 2 are employed as a gate insulation film in the TFT switches 4. The insulation film 15 is, for example, formed from a material such as SiN_xby, for example, Chemical Vapor Deposition (CVD) film forming.

A semiconductor active layer 8 is formed with an island shape on the insulation film 15 above each of the gate electrodes 2. The semiconductor active layer 8 is a channel portion of the TFT switch 4 and is, for example, formed from an amorphous silicon film.

A source electrode 9 and a drain electrode 13 are formed in a layer above these. The wiring layer in which the source electrode 9 and the drain electrode 13 are formed also has the signal line 3 and the common electrode line 25 running parallel to the signal line 3 formed therein. The source electrode 9 is connected to the signal line 3. The wiring layer in which the signal lines 3, the source electrodes 9 and the common electrode lines 25 are formed (this wiring layer is referred to below as “the second signal wiring layer”) is formed from Al or Cu, or a layered film mainly composed of Al or Cu. However, the material of the second signal wiring layer is not limited thereto.

A contact layer (not shown in the drawings) is formed between the semiconductor active layer 8 and both the source electrode 9 and the drain electrode 13. The contact layer is an impurity doped semiconductor of, for example, impurity doped amorphous silicon or the like. Each of the TFT switches 4 is configured with such a configuration.

A TFT protection layer 11 is formed over substantially the whole surface (substantially all regions) of the pixel region 20A where the pixels 20 are situated above the substrate 1 so as to cover the semiconductor active layer 8, the source electrodes 9, the drain electrodes 13, the signal lines 3 and the common electrode lines 25. The TFT protection layer 11 is formed, for example, from a material such as SiN_xby, for example, CVD film forming.

A coated intermediate insulation film 12 is formed on the TFT protection layer 11. The intermediate insulation film 12 is formed from a low permittivity (relative permittivity εr=2 to 4) photosensitive organic material (examples of such materials include positive-working photosensitive acrylic resin materials with a base polymer formed by copolymerizing methacrylic acid and glycidyl methacrylate, mixed with a naphthoquinone diazide positive-working photosensitive agent) at a film thickness of 1 to 4 μm. In the radiation detector 10 according to the present exemplary embodiment, inter-metal capacitance between metal disposed in the layers above the intermediate insulation film 12 and below the intermediate insulation film 12 is suppressed to a small capacitance by the intermediate insulation film 12. Generally such materials also function as a flattening film, exhibiting an effect of flattening out steps in the layers below. A reduction in absorption efficiency and an increase in leak current due to unevenness of the semiconductor layer 6 can thereby be suppressed since the profile is flattened for the semiconductor layer 6 disposed above the intermediate insulation film 12. A contact hole 16 and a contact hole 22A are formed in the intermediate insulation film 12 and the TFT protection layer 11 at, respectively, positions facing each of the drain electrodes 13 and positions on the irradiated face side of the region where each of the scan lines 101 is formed.

A lower electrode 14 of each of the sensor portions 103 is formed on the intermediate insulation film 12 so as to cover the pixel region 20A while also filling the contact hole 16. The lower electrode 14 is connected to the drain electrode 13 of the TFT switch 4. If the thickness of the semiconductor layer 6, described later, is about 1 μm there are substantially no limitations to the material of the lower electrode 14, as long as it is an electrically conductive material. The lower electrode 14 may therefore be formed using a conductive metal such as an aluminum material or indium tin oxide (ITO).

However, there is insufficient light absorption in the semiconductor layer 6 if the film thickness of the semiconductor layer 6 is thin (about 0.2 to 0.5 μm). An alloy or layered film with a main component of a light blocking metal may be employed for the lower electrode 14 in order to prevent an increase in leak current occurring due to light illumination onto the TFT switch 4.

The semiconductor layer 6 is formed on the lower electrode 14 and functions as a photodiode (a photoelectric conversion element). In the present exemplary embodiment, a photodiode of PIN structure is employed as the semiconductor layer 6. The semiconductor layer 6 is formed from the bottom with an n⁺layer, an i layer and a p⁺ layer stacked on each other in order.

The semiconductor layer 6 may be configured with an organic photoelectric conversion element. It is preferable for such an organic photoelectric conversion element to have an absorption peak wavelength as close as possible to the emission peak wavelength of the scintillator 70 in order to most efficiently absorb light emitted by the scintillator 70. While ideally the absorption peak wavelength of the organic photoelectric conversion material matches the emission peak wavelength of the scintillator 70, it is possible to achieve sufficient absorption of light emitted from the scintillator 70 as long as there is a small difference between the two peak wavelengths. More specifically, the difference between the absorption peak wavelength of the organic photoelectric conversion material and the emission peak wavelength to radiation of the scintillator 70 is preferably 10 nm or smaller, and is more preferably 5 nm or smaller.

Examples of organic photoelectric conversion materials capable of satisfying such conditions include, for example, quinacridone organic compounds and phthalocyanine organic compounds. As shown in FIG. 6, CsI(Tl) has an emission peak wavelength at 565 nm, and emits light including wavelengths over a wide wavelength region (400 nm to 700 nm). However, quinacridone is sensitive to light in the wavelength region 430 nm to 620 nm. Since the absorption peak wavelength in the visible region for quinacridone is at 560 nm, it is therefore possible to achieve a principle wavelength difference of 5 nm or smaller in a case in which quinacridone is employed as the organic photoelectric conversion material and CsI(Tl) is employed as the material for the scintillator 70. The charge amount generated in the photoelectric conversion substrate 60 can accordingly be made substantially as large as possible. The semiconductor layer 6 therefore preferably employs an organic photoelectric conversion material formed with quinacridone.

In the present exemplary embodiment the lower electrode 14 is made larger than the semiconductor layer 6. Note that in a case in which the thickness of the semiconductor layer 6 is thin (for example 0.5 μm or less) a light blocking metal may be additionally disposed so as to cover each of the TFT switches 4 in order to prevent light from being incident to the TFT switch 4.

A separation of 5 μm or greater is preferably secured between the edge portions of the lower electrodes 14 made from a light blocking metal and the channel portions of the TFT switches 4 in order to suppress light arising from light scattering and reflection within the device from being incident to the TFT switches 4.

A protection insulation film 17 is formed on the intermediate insulation film 12 and the semiconductor layer 6. The protection insulation film 17 is provided with apertures at each portion where the semiconductor layers 6 are disposed. Upper electrodes 7 are formed on the semiconductor layer 6 and the protection insulation film 17 so as to at least cover each of the apertures in the protection insulation film 17. A material with high light-transparency such as ITO or Indium Zinc Oxide (IZO) is employed for example for the upper electrodes 7. In the present exemplary embodiment, each of the upper electrodes 7 also functions as a conducting member for connection to the respective common electrode line 25 disposed in a lower layer for supplying a bias voltage to the upper electrode 7. As shown in FIG. 5, each of the common electrode lines 25 is connected through the contact hole 22A provided in the intermediate insulation film 12 to a contact pad 24 formed in the lower electrode 14 layer. Each of the upper electrodes 7 is also electrically connected to the respective common electrode line 25 due to the upper electrode 7 covering over the contact hole 22B provided in the protection insulation film 17. Configuration may be made such that the upper electrode 7 and the conducting member for connecting the upper electrode 7 to the common electrode lines 25 are formed from metal in different layers to each other.

A flattening layer 18 for surface flattening is formed over the upper electrode 7 and the protection insulation film 17. The flattening layer 18 is an insulating layer formed, for example, from a material such as SiN_xwith a thickness of 1 μm to 10 μm. The conduction film 30 is formed on the flattened flattening layer 18. The conduction film 30 in the present exemplary embodiment prevents static buildup. In particular, the conduction film 30 prevents static buildup on the surface of the photoelectric conversion substrate 60 (the conduction film 30) by connecting the conduction film 30 to ground such as in a case such as performing surface treatment to the surface of the photoelectric conversion substrate 60 (the conduction film 30) for forming the scintillator 70 on the photoelectric conversion substrate 60. In case in which static buildup occurs on the surface of the photoelectric conversion substrate 60 (the conduction film 30) electrostatic destruction may occur to the sensor portions 103 of the photoelectric conversion substrate 60. Therefore the conduction film 30 in the present exemplary embodiment is formed over the whole face of the flattening layer 18 (or over substantially the whole face), and is formed over the whole face of the pixel region 20A in the present exemplary embodiment. Examples of substances which may be employed for the conduction film 30 include ITO and organic conductive polymer films. The film thickness and resistance of the conduction film 30 are determined from the perspective of static buildup prevention. Specific examples thereof include a film thickness of several tens to several hundreds of nm and a resistance of 10¹⁰Ω or lower. Note that resistance values in the present exemplary embodiment are measured according to the standard of ASTM D257.

The conduction film 30 in the present exemplary embodiment is connected to the selection section 54 through the connection line 52 (see FIG. 1). The conduction film 30 and the connection line 52 are integrally formed in the present exemplary embodiment. The conduction film 30 is applied with a given voltage (bias voltage, internal power source voltage or ground voltage) by the selection section 54 selecting the contact destination through the connection line 52 as the bias power source 110, the internal power source 56 or ground (including grounds other than FGND of the housing 80).

The conduction film 30 in the present exemplary embodiment also absorbs some long wavelength components of the emission wavelengths of the scintillator 70. Adjacent pixels 20 readily receive light if oblique light is incident to the photoelectric conversion substrate 60 (the conduction film 30). As shown in FIG. 7, short wavelength components (for example blue light and green light) are readily refracted and are not received by the sensor portions 103 of the adjacent pixels 20. However, long wavelength components (for example red light) are less readily refracted and so more readily received by the sensor portions 103 of the adjacent pixels 20, as shown in FIG. 8. Blurring of images therefore may occur due to long wavelength components.

FIG. 9 illustrates the refractive index of ITO that serves as a specific example of the conduction film 30. In a specific example of the scintillator 70 employing CsI, the refractive index of ITO in the emission wavelength region of CsI does not substantially differ from the refractive index of CsI (1.77). The emission peak wavelength of CsI is 550 nm, and since the refractive index of ITO for this wavelength is about 1.75, the refractive indexes can be treated as being substantially the same. Consequently, in the emission peak wavelength region even oblique incident light transmits without refraction occurring due to differences in material. The conduction film 30 of the present exemplary embodiment cuts off long wavelength components from such oblique incident light. In order to achieve this, a colorant for cutting off the long wavelength components is mixed into the conduction film 30 of the present exemplary embodiment. As a specific example, a cyan colorant may be mixed into the conduction film 30 to cut off long wavelength components outside the quinacridone absorption wavelength region shown in FIG. 6 (red light: wavelengths 620 nm to 750 nm). Examples of inorganic blue colorants that may be employed therefor include ultramarine blue and Prussian blue (potassium ferrocyanide). Examples of organic blue colorants that may be employed therefor include phthalocyanine, anthraquinone, indigoid and carbonium. Organic colorants are preferably employed in a case in which the radiation detector 10 is employed with Irradiation Side Sampling (ISS) in order for more of the radiation to be allowed to reach the scintillator 70, since inorganic colorants more readily absorb radiation than organic colorants due to containing elements with larger atomic numbers.

Note that it is preferable to absorb as much red light as possible. Since oblique incident light is readily received by adjacent pixels 20 in a case in which the size of the pixels 20 is small (for example 100 μm or less), the amount of colorant mixed in may be increased in such cases so as to raise the absorptance of red light. The amount of colorant contained in the conduction film 30 may therefore be determined according to such factors as the size of the pixels 20.

Examples of colorant include pigments and dyes. Pigments are present as particles in a resin, whereas dyes are present fused with a resin. Note that the colorants mentioned above may also be mixed into the flattening layer 18 in order to cut off even more of the long wavelength components.

Explanation follows regarding a configuration of the selection section 54 in the present exemplary embodiment. FIG. 10 schematically illustrates an example of the selection section 54 of the present exemplary embodiment. As a specific example of the present exemplary embodiment, the selection section 54 is configured by a switching element. Examples of switching elements include, for example, a MOS transistor. Such a switching element selects as the connection destination of the connection line 52, the bias power source 110 (the common electrode lines 25), the internal power source 56 (the power source supply lines 57), or ground (mainly the FGND of the housing 80) (the ground line 59) according to a control signal input from the controller 106.

In the present exemplary embodiment the voltage (given voltage) to be applied to the conduction film 30 is pre-determined according to the operation mode of the radiographic image capture device 100, and the controller 106 outputs a control signal to the selection section 54 such that the given voltage is applied.

Due to the provision of the flattening layer 18 as an insulation layer between the conduction film 30 and each of the sensor portions 103 in the photoelectric conversion substrate 60 of the present exemplary embodiment, a condenser is formed by the flattening layer 18, the conduction film 30 and the sensor portion 103. Therefore deterioration of radiographic image quality may occur due to being affected by accumulated charge in the condenser, or due to being affected by the electric potential of the conduction film 30 becoming unstable. Therefore in the present exemplary embodiment, as an example, in case of a radiographic image capture mode with an emphasis on image quality, the selection section 54 selects such that the conduction film 30 and the bias power source 110 are connected together. Or, for example, in case of a power save mode (such as in an interval before the next time of image capture), selection is made such that the conduction film 30 and the internal power source 56 are connected together. Or, for example, if emphasis is placed on shielding such a case of preventing static buildup, selection is made such that the conduction film 30 is connected to ground (FGND of the housing 80). Note that there is no limitation thereto, and control may be performed so as to select the connection destination of the conduction film 30 according to other conditions and other modes. In the present exemplary embodiment the conduction film 30 is connected to ground during fabrication of the radiation detector 10, from the perspective of preventing static buildup during fabrication of the radiation detector 10 in such processes as surface treatment. In such cases any ground external to the photoelectric conversion substrate 60 (the radiation detector 10) may be employed without particular limitation.

Explanation follows regarding an example of fabrication processes of the pixels 20 portions of the radiation detector 10 according to the present exemplary embodiment.

In the present exemplary embodiment, the gate electrodes 2 and the scan lines 101 are formed as the first signal wiring layer on the substrate 1, thereby forming the first signal wiring layer. The insulation film 15, the semiconductor active layer 8, and a contact layer (not shown in the drawings) are then deposited in this sequence on the first signal wiring layer. The semiconductor active regions are then formed by selectively dry etching the semiconductor active layer 8 and the contact layer formed from an impurity doped semiconductor down to the insulation film 15 so as to form semiconductor active regions. The signal lines 3, the source electrodes 9, the drain electrodes 13, and the common electrode lines 25 are then formed as the second signal wiring layer as a layer above the insulation film 15 and the semiconductor active layer 8. Then the contact layer and a portion of the semiconductor active layer 8 are removed by further dry etching to form a channel region.

The TFT protection layer 11 and the intermediate insulation film 12 are then also formed in sequence. There are cases in which the TFT protection layer 11 and the intermediate insulation film 12 are formed as a single inorganic material body, cases in which they are formed as stacked layers of a protection-insulation film formed from an inorganic material and an intermediate insulation film formed from an organic material, and cases in which they are formed as a single layer intermediate insulation film formed from an organic material. In the present exemplary embodiment, in order to suppress the capacitance between the lower layer common electrode lines 25 and the lower electrode 14 and stabilize the characteristics of the TFT switches 4, a stacked layer structure is adopted of a photosensitive intermediate insulation film 12 and the TFT protection layer 11 formed from an inorganic material. Then patterning of the TFT protection layer 11 is performed using photolithographic technology. Note that this step is not required if there is no TFT protection layer 11 disposed.

The lower electrode 14 is formed by using a sputtering method to deposit a metal material such as an aluminum material or ITO onto the top layer of the layers described above, and then performing patterning. The semiconductor layer 6 is then formed. The semiconductor layer 6 may be formed using a CVD method in a case in which the semiconductor layer 6 is an organic photoelectric conversion material. The film thickness is preferably 30 nm to 300 nm, more preferably 50 nm to 250 nm, and most preferably 80 nm to 200 nm. In a case in which an inorganic photoelectric conversion material is employed the semiconductor layer 6 may be formed using a CVD method to deposit each layer of n+, i, and p+, in sequence from the bottom layer. The film thicknesses are, for example, n+ layer 50 nm to 500 nm, i layer 0.2 μm to 2 μm, p+ layer 50 nm to 500 nm. Each layer of the semiconductor layer 6 is deposited in sequence and patterned with photolithographic technology. The semiconductor layer 6 is then completed by selectively etching with the lower layer of the intermediate insulation film 12 using dry etching or wet etching. Note that configuration may be made as a PIN diode by depositing layers in the sequence p+, i, n+, instead of depositing layers in the sequence n+, i, p+.

The protection insulation film 17 formed from an SiNx film is then deposited so as to cover the semiconductor layer 6 using, for example, a CVD method and then patterning is performed thereto so as to form apertures therein. Note that while an example has been given in which the protection insulation film 17 is formed from SiNx using CVD film forming, there is no limitation to SiNx and any insulating material may be employed. The connection locations of the upper electrode 7 and the common electrode lines 25 are then formed. Above the layers that have been formed as described above a transparent conductive material such as ITO is deposited using a sputtering method, and the upper electrode 7 is formed by patterning. The SiNx flattening layer 18 is then deposited using for example CVD method so as to cover the upper electrode 7 and the protection insulation film 17, flattening out undulations in the surface arising, for example, due to the semiconductor layer 6. While an example has been given here in which the flattening layer 18 is formed from SiNx using a CVD method, there is no limitation to SiNx and any insulating material may be employed. The conduction film 30 and the connection line 52 are then formed on the flattening layer 18 using a sputtering method with a transparent conductive material such as ITO. The film thickness of the conduction film 30 may be several tens of nm to several hundreds of nm, and the resistance of the conduction film 30 may be 10¹⁰Ω or less. Other layers such as a protection layer may also be formed on the conduction film 30. In the present exemplary embodiment the conduction film 30 thus formed on the surface of the pixels 20 (the pixel region 20A) is connected to the selection section 54. The photoelectric conversion substrate 60 is thereby prepared by the processes described above.

After the photoelectric conversion substrate 60 has been prepared, as shown in FIG. 11, the following surface treatment processes are performed to the surface of the photoelectric conversion substrate 60 (the conduction film 30) as pre-processing in order to enhance adhesion to the scintillator 70, film 30. Such surface treatment is performed with the connection line 52 placed by the selection section 54 in a grounded state, as shown in FIG. 11, namely with the conduction film 30 connected to ground through the selection section 54. Examples of surface treatment include vacuum plasma processing, atmospheric-pressure plasma processing and corona discharge treatment. By connecting the conduction film 30 to ground through the selection section 54 while such surface treatment is being performed, static buildup in the conduction film 30 can be prevented due to charge generated by surface treatment on the surface of the conduction film 30 flowing to ground. Electrostatic damage to the sensor portions 103 of the photoelectric conversion substrate 60 can accordingly be prevented. Vacuum plasma processing is preferably performed as such surface treatment from the perspective of improving adhesion to the scintillator 70.

The scintillator 70 is then formed on the conduction film 30 of the photoelectric conversion substrate 60 that has been subjected to the above surface treatment. In the present exemplary embodiment, the scintillator 70 is formed by directly depositing CsI(Tl) on the photoelectric conversion substrate 60 (the conduction film 30) using a vapor deposition method such as vacuum deposition. In the present exemplary embodiment, in case of forming the crystal phases on the photoelectric conversion substrate 60, the non-columnar portion 71 is formed first and then the columnar portion 72 is formed. As shown in FIG. 12, in the present exemplary embodiment, similarly to when performing surface treatment processes (see FIG. 11), the conduction film 30 is also connected to ground through the selection section 54 during the processes for forming the scintillator 70. While it is not always necessary for the conduction film 30 to be in a ground-connected state through the selection section 54 during these scintillator-forming-processes, these processes may be performed with the conduction film 30 in a ground-connected state through the selection section 54 from the perspective of preventing electrostatic destruction due to static buildup.

In the present exemplary embodiment the above processing completes fabrication of the radiation detector 10.

As explained above, the photoelectric conversion substrate 60 of the radiation detector 10 of the present exemplary embodiment is flattened due to provision of the flattening layer 18 on the faces of the TFT switches 4 and the sensor portions 103 that have been formed on the substrate 1, and the conduction film 30 is formed over substantially the whole face of the flattening layer 18 (the whole face of the pixel region 20A in the present exemplary embodiment) in order to prevent static buildup. The conduction film 30 is also integrally formed with the connection line 52 and connected to the selection section 54. The selection section 54 also selects as the connection destination for the connection line 52 one destination out of the bias power source 110, the internal power source 56, or ground (including FGND of the housing 80) according to a control signal input from the controller 106. The scintillator 70 is formed on the photoelectric conversion substrate 60 (on the conduction film 30), and the scintillator 70 is equipped with the non-columnar portion 71 and the columnar portion 72, provided in sequence for the side nearest to the photoelectric conversion substrate 60.

In the thus configured present exemplary embodiment, due to making it possible to connect the conduction film 30 to ground using the selection section 54, surface treatment can be performed to the surface of the photoelectric conversion substrate 60 (the conduction film 30) for improving adhesion to the scintillator 70 while the conduction film 30 is placed in a ground-connected state. Static buildup on the photoelectric conversion substrate 60 (the conduction film 30) can accordingly be prevented due to charge generated by surface treatment flowing to ground. Electrostatic damage to the sensor portions 103 due to static buildup can accordingly be prevented. The adhesion between the photoelectric conversion substrate 60 and the scintillator 70 can also be improved due to being able to employ vacuum plasma processing as surface treatment since static buildup can be prevented.

The given voltage can be applied as the voltage to the conduction film 30 by using the selection section 54 to select the connection destination of the connection line 52, and the conduction film 30 can be fixed (clamped) to the given voltage. Namely, in the radiation detector 10 provided with the photoelectric conversion substrate 60 of the present exemplary embodiment, electrostatic damage to the sensor portions 103 can be prevented and also the conduction film 30 can be set to the given voltage.

The conduction film 30 can accordingly be clamped to the electric potential that is optimal for the state and mode of the radiographic image capture device 100, enabling the radiation detector 10 to approach a more ideal state.

Note that a conducting layer 90 may be formed on the reverse side of the substrate 1 of the photoelectric conversion substrate 60 (the reverse side where the TFT switches 4 or the semiconductor layer 6 are not formed), as shown in FIG. 13. The conducting layer 90 prevents static buildup on the surface of the photoelectric conversion substrate 60 (the radiation detector 10). Examples of substances which may be employed for the conducting layer 90 include ITO and organic conductive polymer films. Further, the thickness and resistance of the conducting layer 90 may be determined from the perspective of static buildup prevention. Note that the conducting layer 90 may have substantially the same configuration as the conduction film 30. Although the timing for forming the conducting layer 90 is not limited in particular, the conducting layer 90 should be formed on the reverse side of the substrate 1 before forming the scintillator 70, in order to prevent static buildup on the surface of the photoelectric conversion substrate 60 in a case of forming the scintillator 70. The conducting layer 90 preferably covers an area corresponding to the pixel region 20A, and more preferably is as large as or larger than the conduction film 30. Further, the conducting layer 90 may be formed so as to cover the whole reverse side of the substrate 1, and the size of the conducting layer 90 may be determined from the perspective of static buildup prevention.

A given voltage is applied to the conducting layer 90, similarly to the conduction film 30. In the present exemplary embodiment, the conducting layer 90 is electrically connected to the conduction film 30. Specifically, as shown in FIG. 13, the conducting layer 90 is connected to the connection line 52 through a connection line 52 A. The conducting layer 90 and the conduction film 30 are thereby clamped to the given voltage and become equipotential. Therefore, electrostatic damage to the sensor portions 103 can be prevented more effectively.

Further, a reflection layer 92 may be formed on the scintillator 70 (the columnar portion 72) as shown in FIG. 13. The reflection layer 92 reflects light that is emitted in the scintillator 70 to the photoelectric conversion substrate 60. Further, the reflection layer 92 of the present exemplary embodiment prevents static buildup on the surface of the radiation detector 10. Metallic material that transmits radiation and reflects light effectively, such as Al, is preferable for substances employed for the reflection layer 92. Further, the thickness and resistance of the reflection layer 92 may be determined from the perspective of static buildup prevention. The reflection layer 92 is formed so as to cover at least the upper surface of the scintillator 70. Note that the reflection layer 92 may be formed so as to cover side surfaces of the scintillator 70, and the size of the reflection layer 92 may be determined from the perspective of reflection or static buildup prevention.

A given voltage is applied to the reflection layer 92, similarly to the conduction film 30. In the present exemplary embodiment, the reflection layer 92 is electrically connected to the conduction film 30. Specifically, as shown in FIG. 13, the reflection layer 92 is connected to the connection line 52 through a connection line 52B. The reflection layer 92 and the conduction film 30 are thereby clamped to the given voltage and become equipotential. Therefore, electrostatic damage to the sensor portions 103 can be prevented more effectively.

Note that a protection layer of material such as PET (polyethylene terephthalate), not shown in FIG. 13, may be formed between the reflection layer 92 and the scintillator 70, or on the reflection layer 92. Further, although both the conducting layer 90 and the reflection layer 92 are shown in FIG. 13, a configuration is possible so that the only one of the conducting layer 90 and the reflection layer 92 is formed.

In the present exemplary embodiment explanation has been given of an example in which the scintillator 70 is directly vacuum deposited on the photoelectric conversion substrate 60, however there is no limitation thereto. The scintillator 70 may be stuck to the photoelectric conversion substrate 60 using for example an adhesive resin. Static buildup can also be prevented and electrostatic damage to the sensor portions 103 can also be prevented in such cases by, similarly to as described above, using the selection section 54 to place the conduction film 30 in a ground-connected state when performing surface treatment to the surface of the photoelectric conversion substrate 60 (the conduction film 30), in order to for example improve adhesion,

In the above exemplary embodiment, detailed explanation has been given of an example in which the selection section 54 is provided to the photoelectric conversion substrate 60, however there is no limitation thereto. For example, there are no particular limitations to the location of the selection section 54, and the selection section 54 may be provided to another location of the radiation detector 10, or provided on another substrate installed in the housing 80 of the radiographic image capture device 100. In such cases that, for example, the selection section 54 is connected to ground or a bias voltage, the connection destination of the conduction film 30 may be selected selectively according to each of the above modes by employing instructions such as from the controller 106.

The given voltage is also not limited to the examples given above, and may for example be a signal ground, or may be a voltage determined according to the specification of the radiographic image capture device 100.

The photoelectric conversion substrate 60 is employed in the present exemplary embodiment, however a flexible substrate may be employed. An ultra-thin glass substrate produced by recently developed float technology may be applied as a substrate for such a flexible substrate in order to improve the transmissivity to radiation. Examples of ultra-thin glass substrates that may be applied in such cases include, for example, substrates described in the announcement published online, online search Aug. 20, 2011 “Asahi Glass Company (AGC) Develops Worlds Thinnest Sheet Float Glass at Just 0.1 MM”, Internet <URL: http://www.agc.com/news/2011/0516.pdf>.

Note that the configuration and operation of the selection section 54, the photoelectric conversion substrate 60, the radiation detector 10 and the radiographic image capture device 100 explained in the above exemplary embodiment are merely examples thereof. Various changes within a range not departing from the spirit of the present invention are possible according to circumstances.

Furthermore the radiation explained in the present exemplary embodiment is not particularly limited, and radiation such as X-rays and y-rays may be employed.

Although explanation has been given of a case in which the semiconductor layer 6 is employed for the sensor portions 103, the present invention is not limited thereto and a CMOS sensor may be applied.

Number	Date	Country	Kind
2011-185236	Aug 2011	JP	national
2012-165136	Jul 2012	JP	national

PHOTOELECTRIC CONVERSION SUBSTRATE, RADIATION DETECTOR, AND RADIOGRAPHIC IMAGE CAPTURE DEVICE

Information

Publication Number

Date Filed

Date Published

Inventors

Original Assignees

CPC

US Classifications

International Classifications

Abstract

Description

Claims

Priority Claims (2)