JP3691077B2 - Radiation detecting element and manufacturing method thereof - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a radiation detection element that is attached to an X-ray imaging apparatus or the like and converts an X-ray image transmitted through a subject into an electrical signal.
[0002]
[Prior art]
A schematic configuration of a general X-ray imaging apparatus is shown in FIG. X-rays are emitted from the X-ray source 2 toward the subject 3 under the control of the drive control unit 1. The irradiated X-rays pass through the subject 3, and an image of a predetermined portion of the subject 3 is picked up by the X-ray detector 4. This imaging data is obtained as an electrical signal and is displayed on the monitor 5. At the same time, the imaging data is converted into digital data by the A / D converter 6 and stored in the video recording device 7. The stored digital imaging data is displayed on the display device 8 as appropriate. The central control device 9 controls the X-ray irradiation amount from the X-ray source 2 to the subject 3 via the drive control unit 1 based on the imaging data captured by the video recording device 7, and always appropriate imaging data. Control the system so that Further, the central control device 9 transfers the image data captured by the video recording device 7 to the video storage device 10 as necessary, and stores the image data.
[0003]
A cross-sectional structure of the X-ray detector 4 is shown in FIG. X-rays that have passed through the protective film 41 through the subject 3 are converted into light in the scintillator 42. The converted light further enters the semiconductor detection unit 44 via the protective film 43. The internal configuration of the semiconductor detection unit 44 is shown in FIG. In other words, the light incident through the protective film 43 is photoelectrically converted by the photodiode 45 and accumulated in the capacitor 46. The accumulated electric charges are read out at a predetermined timing through the TFT transistor 47 controlled by the shift register 48. The read imaging data is displayed on the monitor 5 and converted into digital data by the A / D converter 6. In FIG. 5, for simplicity of explanation, the photodiode 45 is simply described as a one-dimensional configuration, but in actuality, it has a two-dimensional configuration.
[0004]
Conventionally, an X-ray detector having a structure in which this type of scintillator and a semiconductor detector (photoelectric conversion film) are combined is mainly used in the following two methods / structures in a one-dimensional or two-dimensional radiation image sensor. Manufactured by. The first is a structure in which a powder phosphor is applied to the semiconductor detection unit. This powder phosphor is applied to the semiconductor detector by sedimentation, centrifugation, or the like. The second is an X-ray detector having a structure in which a scintillator is formed of a CsI vapor-deposited crystal and the CsI vapor-deposited crystal is combined with a photoelectric conversion film. However, a sufficient amount of emitted light cannot be obtained unless the CsI vapor-deposited crystal is usually formed through a baking process of 300 ° C. or higher. Therefore, when a-Si: H is used for the photoelectric conversion film, it is desirable that CsI is vapor-deposited and fired directly or via a protective film on the a-Si: H film. If the detector is formed with a simple process and structure, the a-Si: H film is deteriorated by heat in the firing process of the CsI crystal. For this reason, conventionally, the CsI crystal was deposited on the fiber plate, and the CsI crystal on the fiber plate was baked while being separated from the a-Si: H film. After firing, the fiber plate and the a-Si: H photoelectric conversion film are coupled to form a radiation image sensor.
[0005]
[Problems to be solved by the invention]
However, in the conventional radiation detector having a structure in which a powder phosphor is applied to the conventional semiconductor detector, the X-ray sensitivity and resolution are both good due to the light emission characteristics of the powder phosphor itself. It was not realized. On the other hand, in the radiation detector using the conventional CsI vapor-deposited crystal, X-ray detection characteristics excellent in emission sensitivity and resolution are realized by the characteristics of the CsI vapor-deposited crystal itself. However, since the fiber plate is used, there are the following problems. That is, since the light generated by the scintillator enters the photoelectric conversion film through the fiber plate, a part of the light is reflected and absorbed by the fiber plate. For this reason, the amount of scintillation light finally incident on the photoelectric conversion film is reduced, and the detection sensitivity of the radiation detector is deteriorated. Further, since it is difficult to form a fiber plate with a large area, it is difficult to increase the size of the radiation detector itself, and it has not been possible to image a large subject. In addition, there is a problem that the product cost is increased as much as the fiber plate is used.
[0006]
The present invention relates to a photoelectric conversion layer in which photodiodes made of a-Si: H that receive light to generate photocarriers are formed in an array, a polyimide protective film formed on the photoelectric conversion layer, and the photoelectric conversion layer. After forming a protective film on the conversion layer, the CsI vapor-deposited crystal is formed on the protective film by vapor deposition, and then is thermally activated while cooling the photoelectric conversion layer and generates light upon receiving radiation. And a scintillator layer. A radiation detection element comprising the scintillator layer is provided.
[0007]
A step of forming a photoelectric conversion layer that generates photocarriers when receiving light, a step of forming a scintillator layer that generates light when receiving radiation directly or via a protective film on the photoelectric conversion layer, and a scintillator layer Forming an infrared absorption film having heat resistance capable of withstanding the activation temperature of the light and transmitting radiation directly on the scintillator layer or via a light reflection film, and infrared rays on the infrared absorption film while cooling the photoelectric conversion layer And a step of activating the scintillator layer by irradiating light containing the radiation detecting element.
[0008]
[Action]
Since the scintillator layer is activated while the photoelectric conversion layer is cooled, the scintillator layer made of CsI or the like is formed on the photoelectric conversion layer directly or via a protective film.
[0009]
【Example】
FIG. 1 is a view showing a first embodiment in which the radiation detection element of the present invention is applied to an X-ray detector. This X-ray detector is used in the X-ray imaging apparatus shown in FIG. A method for manufacturing the X-ray detector according to the first embodiment will be described below.
[0010]
In the photoelectric conversion layer 21, photodiodes made of a-Si: H are formed in an array, and a photoelectric conversion circuit similar to the circuit shown in FIG. 5 is configured. A protective film 22 made of polyimide is first formed on the photoelectric conversion layer 21 to a thickness of 2 μm. Next, a scintillator layer 23 made of CsI vapor-deposited crystal is formed on the protective film 22 to a thickness of 500 μm. Next, carbon powder is applied on the scintillator layer 23 to a thickness of 6 μm to form an infrared absorption layer 24 (see FIG. 1A). This infrared absorption layer 24 has a property of transmitting radiation and has heat resistance capable of withstanding an activation temperature of a scintillator layer 23 described later.
[0011]
Next, the photoelectric conversion layer 21 is placed in contact with the pipe 25 made of a material having good thermal conductivity. Next, a −40 ° C. coolant is caused to flow through the pipe 25 to cool the lower photoelectric conversion layer 21. And while this cooling is performed, light including infrared light is irradiated to the upper infrared absorbing layer 24 from the infrared lamp 26. The irradiated light is efficiently absorbed by the infrared absorption layer 24, and the infrared absorption layer 24 is heated. The temperature rise of the infrared absorption layer 24 is conducted to the scintillator layer 23, and the scintillator layer 23 is efficiently heated to 300 ° C. or more and activated (see FIG. 5B).
[0012]
Next, the infrared absorption layer 24 is removed, and a protective film 27 made of polyimide is formed on the exposed scintillator layer 23. Next, a light reflecting film 28 made of an Al sheet having a thickness of 0.1 mm is covered on the protective film 27, and the X-ray detector is completed (see FIG. 5C). The light reflecting film 28 prevents light generated in the scintillator layer 23 from leaking to the upper layer portion and prevents stray light from being generated.
[0013]
In the above-described embodiment, the infrared absorption layer 24 is removed after the activation process of the scintillator layer 23. However, the protective film 27 and the light reflection film 28 may be formed on the infrared absorption layer 24 without being removed. (See (d) in the figure). However, when formed in this manner, the infrared absorption layer 24 absorbs the return light of the scintillation light, and the above function of the light reflection film 28 does not function. Therefore, it is desirable to remove the infrared absorption layer 24.
[0014]
According to the first embodiment, since the scintillator layer 23 is activated while the photoelectric conversion layer 21 is cooled as described above, the photoelectric conversion layer 21 is not affected by heat due to infrared irradiation. Therefore, the scintillator layer 23 made of CsI is formed on the photoelectric conversion layer 21 without deteriorating the characteristics of the photoelectric conversion layer 21. For this reason, an X-ray detector is comprised, without producing the various problems which the conventional X-ray detector comprised using the fiber plate had. That is, the detection sensitivity of the X-ray detector is improved without reducing the amount of scintillation light incident on the photoelectric conversion layer 21. Further, since there is no restriction on the possible formation area of the fiber plate, the radiation image sensor itself can be easily increased in size. Further, the product cost is reduced by the amount not using the fiber plate. Further, since the scintillator layer 23 is formed of CsI vapor-deposited crystals, it has better X-ray sensitivity and resolution than a radiation detector using a powder phosphor.
[0015]
The X-ray sensitivity (70 kVp, W target evaluation) of the X-ray detector according to the first embodiment actually obtained was five times that before the scintillator layer 23 was heated. In addition, the quantum efficiency of the photodiode array itself made of a-Si: H in the photoelectric conversion layer 21 was not actually decreased.
[0016]
Next explained is an X-ray detector according to the second embodiment of the invention. The manufacturing method of this X-ray detector is shown in FIG. 2 and manufactured as follows.
[0017]
In the photoelectric conversion layer 31, a photodiode array made of a-Si: H is formed as in the first embodiment. A protective film 32 made of polyimide is formed on the photoelectric conversion layer 31 to a thickness of 2 μm, and a scintillator layer 33 made of CsI deposited crystal is formed on the protective film 32 to a thickness of 400 μm. Next, a light reflection film 34 made of an Al vapor deposition film is formed on the scintillator layer 33 to a thickness of 0.4 μm. The light reflecting film 34 prevents light generated in the scintillator layer 33 from leaking to the upper layer portion and prevents stray light from being generated, as in the first embodiment. Next, carbon is deposited on the light reflecting film 34 to a thickness of 4 μm by sputtering to form an infrared absorption layer 35 (see FIG. 2A). The infrared absorbing film 35 has a property of transmitting radiation and has heat resistance capable of withstanding an activation temperature of a scintillator layer 33 described later.
[0018]
Next, as in the first embodiment, the photoelectric conversion layer 31 is placed in contact with the pipe 25. Then, a −40 ° C. refrigerant is caused to flow through the pipe 25 to cool the photoelectric conversion layer 31. Infrared light is applied to the infrared absorption layer 35 from the infrared lamp 26 while this cooling is performed. The infrared absorption layer 35 is heated by the irradiated light, and this temperature rise is conducted to the scintillator layer 33 through the light reflection film 34, and the scintillator layer 33 is efficiently heated to 300 ° C. or more and activated. (See (b) in the figure).
[0019]
Next, the infrared absorption layer 35 is removed, and a protective film 36 made of polyimide is formed on the exposed light reflecting film 34, thereby completing the X-ray detector (see FIG. 3C).
[0020]
In the above-described embodiment, the infrared absorption layer 35 is removed after the activation process of the scintillator layer 33. However, the protective film 36 may be formed on the infrared absorption layer 35 without being removed ((d) in the figure). reference). In this embodiment, since the infrared absorption layer 35 is formed in the upper layer portion of the light reflection film 34, even if the infrared absorption layer 35 remains without being removed, the scintillation light is not absorbed by the infrared absorption layer 35, The function of the light reflecting film 34 is sufficiently achieved.
[0021]
Also in the second embodiment, since the scintillator layer 33 is activated while the photoelectric conversion layer 31 is cooled, the characteristics of the photoelectric conversion layer 31 are not deteriorated, and the scintillator layer 33 made of CsI is separated from the photoelectric conversion layer 31. Will be formed on top. For this reason, various problems of the conventional X-ray detector are also eliminated in this embodiment, and the quantum efficiency of the a-Si: H photodiode is increased on the a-Si: H photodiode array capable of increasing the area. It is possible to take advantage of the good characteristics of the CsI vapor-deposited crystal without loss.
[0022]
Also in this example, X-ray sensitivity five times that before scintillator layer 33 was heated was actually obtained. In addition, the quantum efficiency of the photodiode array itself made of a-Si: H in the photoelectric conversion layer 31 was not actually decreased.
[0023]
In each of the above embodiments, a protective film is formed on the photoelectric conversion layer, and the scintillator layer is formed on the protective film. However, the scintillator layer may be formed directly on the photoelectric conversion layer. The same effects as in the above embodiments are obtained.
[0024]
【The invention's effect】
As described above, according to the present invention, since the scintillator layer is activated while the photoelectric conversion layer is cooled, the scintillator layer made of CsI or the like is formed on the photoelectric conversion layer directly or via a protective film. .
[0025]
For this reason, various problems of the conventional radiation detector using the fiber plate and the conventional radiation detector using the powder phosphor are solved, and the radiation detector capable of increasing the area with excellent X-ray sensitivity and resolution. Can be obtained at low cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a manufacturing process of a radiation detector according to a first embodiment of the present invention.
FIG. 2 is a manufacturing process cross-sectional view of a radiation detector according to a second embodiment of the present invention.
FIG. 3 is a block configuration diagram showing a schematic configuration of a general X-ray imaging apparatus.
FIG. 4 is a cross-sectional view showing the structure of a conventional X-ray detector.
FIG. 5 is a circuit diagram showing a simplified configuration of a general photoelectric conversion circuit formed in a photoelectric conversion layer of an X-ray detector.
[Explanation of symbols]
21, 31 ... photoelectric conversion layer, 22, 27, 32, 36 ... protective film, 23, 33 ... scintillator layer, 24, 35 ... infrared absorption layer, 25 ... pipe, 26 ... infrared lamp, 28, 34 ... light reflection film .

Claims (2)

A photoelectric conversion layer in which photodiodes made of a-Si: H that receive light and generate photocarriers are formed in an array;
A polyimide protective film formed on the photoelectric conversion layer;
After the protective film is formed on the photoelectric conversion layer, after being formed on the protective film by vapor deposition, the photoelectric conversion layer is cooled and thermally activated to generate light upon receiving radiation. A scintillator layer of CsI vapor deposited crystals;
A radiation detection element configured to include:   A step of forming a photoelectric conversion layer that generates photocarriers when receiving light, a step of forming a scintillator layer that generates light when receiving radiation directly or via a protective film on the photoelectric conversion layer, and the scintillator layer Forming an infrared absorption film having heat resistance capable of withstanding the activation temperature of the radiation and transmitting radiation directly on the scintillator layer or via a light reflection film, and absorbing the infrared radiation while cooling the photoelectric conversion layer And a step of activating the scintillator layer by irradiating the film with light containing infrared rays.

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