JP2001330677A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously improve the photodetecting sensitivity and the MTF (resolution). SOLUTION: In the radiation detector having a scintillator formed on a sensor base having at least a plurality of photoelectric converters, a radiation shield is formed on the scintillator, and a radioactive ray is made incident from the sensor base side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detecting apparatus for detecting radiation using light obtained in response to incident radiation.

[0002]

2. Description of the Related Art Conventionally, as this type of X-ray detection device,
Photoelectric conversion element represented by PIN type photo sensor and T
A sensor substrate having a configuration in which a switch element such as an FT is arranged two-dimensionally or one-dimensionally is used.

FIG. 7 is a sectional view of a conventional X-ray detector. As shown in FIG. 7, a conventional X-ray detection device has a photoelectric conversion element portion (not shown) composed of a PIN photodiode on a substrate 11 such as glass and a TF as a switch element.
T (not shown) is formed thereon, and an SiN protective film 14 is formed thereon for stabilizing device characteristics. Further, the scintillator layer 16 and Al for improving its moisture resistance are used.
Layer 18 is laminated.

FIG. 8 is an equivalent circuit diagram near the sensor section. 8, 101 is a PIN photodiode,
102 is a TFT, 103 is a signal line, 104 is a gate line, and 105 is a sensor bias line.

FIG. 9 shows the PIN photodiode 1 of FIG.
FIG. 1 is a cross-sectional view of a TFT and a TFT. In FIG.
202 is a gate wiring, 203 is a gate insulating film, 204 is an i-type a-Si active layer, 205 is a SiN layer, and 206 is n ⁺
Type ohmic contact layer, 207 is an SD (source / drain) electrode, 208 is a sensor lower electrode, 210, 21
Reference numerals 1 and 212 denote p, i, and n-type a-Si layers, 209, respectively.
Denotes a sensor upper electrode, and 213 denotes a SiN protective film. In FIG. 9, the sensor bias wiring 105 and the like are not shown.

When an X-ray 15 is incident on such an X-ray detection device from above in FIG. 7, the X-ray 15 is converted into visible light by a scintillator layer 16, and the converted light is converted into a visible light as shown in FIG. It enters the indicated sensor section. And the converted light is
The signal is converted into an electric signal by a sensor and output to a signal processing device (not shown) or the like.

[0007]

However, when X-rays are incident from the scintillator side of the X-ray detector, the X-rays
It is effectively converted to visible light only above the scintillator layer. This is due to the absorption coefficient of the scintillator. Therefore, the converted light needs to travel in the scintillator layer after the conversion, and at that time, it is reflected, absorbed,
By being refracted and scattered, the modulation transfer function (MT
F: Modulation Transfer Function) and light receiving sensitivity are reduced.

FIG. 10 shows the relationship between the thickness of the scintillator layer and the MT.
It is a figure showing relation of F. FIG. 10 shows that the thickness of the scintillator layer exists so as to maximize the relative light emission amount, and that the MTF decreases as the thickness of the scintillator layer increases. Therefore, when trying to increase the MTF, the thickness of the scintillator layer must be reduced.

FIG. 11 is a diagram showing the relationship between the thickness of the scintillator layer and the MTF, similarly to FIG. 10, and shows the relationship between the distance from the optical axis of the light changed by the scintillator layer and the amount of emitted light. . In FIG. 11, t1, t2, and t3 are the thicknesses of the scintillator layers, and FIG.
FIG. 11B shows t2, and FIG. 11C shows t3. Further, these thicknesses have a relationship of t1 <t2 <t3.

Here, in FIGS. 11 (a) to 11 (c), when the thickness of the scintillator layer is increased, the amount of emitted light is increased, and light is diffused in proportion to the amount of light to be diffused from the optical axis. This indicates that the distance increases, and that the MTF decreases as the distance from the optical axis increases due to diffusion of light. That is, as described in FIG. 10, when trying to increase the MTF, the thickness of the scintillator layer must be reduced.

According to FIGS. 11A to 11C, the thickness of the scintillator layer is optimally t2. As described above, conventionally, the thickness of the scintillator layer must be determined based on the balance between the light receiving sensitivity and the MTF. However, there is a trade-off relationship between the light receiving sensitivity and the MTF, and there is a problem that it cannot be improved at the same time. .

Accordingly, an object of the present invention is to improve both the light receiving sensitivity and the modulation transfer function (MTF).

[0013]

In order to solve the above-mentioned problems, the present invention relates to a radiation detecting apparatus in which a scintillator is formed on a sensor base having at least a plurality of photoelectric conversion elements, wherein a radiation shield is provided on the scintillator. Then, radiation is made incident from the sensor substrate side.

That is, according to the present invention, the amount of light incident on the sensor is increased by injecting radiation from the sensor base.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In the embodiment described below, an X-ray detection device will be described as an example of a radiation detection device. However, the present invention is also applied to detection devices other than X-rays, such as α-rays, β-rays, and γ-rays. be able to.

(Embodiment 1) FIG. 1 is a schematic sectional view of an X-ray detector according to Embodiment 1 of the present invention. As shown in FIG. 1, the X-ray detection apparatus according to the present embodiment includes a photoelectric conversion element unit (not shown) and a TFT (not shown) on a plate-like sensor substrate (sensor substrate) 11 made of glass or the like. Is formed thereon, and Si is formed thereon for stabilization of device characteristics.
An N protective film 14 is formed.

The thickness of the sensor substrate 11 is preferably such that the sensor substrate 11 is hardly cracked in the manufacturing process and transmits a large amount of X-rays 15. About 0.7 mm is considered to be this thickness. In the present embodiment, for example, it is 0.7 mm.

Reference numeral 19 denotes P which is an X-ray shielding plate.
1 shows a metal-containing glass substrate such as glass b. Pb
An Al layer 18 is formed on a glass substrate 19 by a sputtering method, and a scintillator layer 16 and a protective layer such as polyethylene terephthalate (PET) (not shown) are formed thereon. In the scintillator layer 16, GOS, CsI,
Amorphous selenium, PbI ₂ , HgI _2, or the like can be used. Here, for example, a GOS phosphor is used as the scintillator layer 16. Then, the Pb glass substrate 19 is attached to the sensor substrate 11 with an epoxy adhesive or the like.

The X-rays 15 enter from the sensor substrate 11 side, are converted into light by the scintillator layer 16 near the photoelectric conversion unit, and reach the photoelectric conversion unit without attenuation. Therefore, light receiving sensitivity and MTF can be improved.

FIG. 2 is a diagram showing the relationship between the relative light emission amount and the modulation transfer function (MTF) with respect to the difference in the thickness of the scintillator layer 16 when the X-ray detector shown in FIG. It is. The relative light emission increases monotonically and M
TF decreases monotonically. In FIG. 2, the broken line indicates the MTF (prior art) at the time of surface incidence. As described above, according to the X-ray detection apparatus of the present embodiment, when the same MTF is realized, a sensor having higher emission intensity can be realized.

Although the glass usually slightly absorbs X-rays, the thickness of the glass constituting the sensor substrate 11 is set to 0.7 mm or less. As shown in FIG. 2, the MTF is improved.

(Embodiment 2) FIG. 3 is a schematic sectional view of an X-ray detector according to Embodiment 2 of the present invention. X shown in FIG.
The line detecting device has the same manufacturing process as that of the first embodiment until the SiN protective film 14 is formed.

The SiN protective layer 14, the scintillator layer 16, the Al layer 18, and the protective layer 1
7 is formed, and a stainless substrate 20 having a thickness capable of sufficiently shielding X-rays is bonded to the protective layer 17 using an adhesive while pressing with a roller or the like. In the present embodiment, as the scintillator layer 16, for example, a cesium iodide (CsI) layer is laminated by a vacuum evaporation method. In the X-ray detection device thus created, the MT shown in FIG.
The improvement of F was seen.

According to this embodiment, since the scintillator layer 16 can be bonded to the sensor substrate 11 without using an adhesive, the incident X-rays 15
Scintillator layer 1 without hindrance by adhesive
Reach 6.

(Embodiment 3) FIG. 4 is a schematic sectional view of an X-ray detector according to Embodiment 3 of the present invention. X shown in FIG.
The line detection device includes an Al layer 18 on a Pb glass substrate 19,
Scintillator layer 16, photoelectric conversion element part (not shown),
Until a TFT (not shown) and a protective layer (not shown) are formed, the same manufacturing process as in the first embodiment is performed.

An organic PET film (PET) substrate 21 on which the SiN protective film 14 is formed is adhered on the substrate 21 by a roller 22. In the present embodiment, by providing the photoelectric conversion element and the TFT on the scintillator layer 16 side, the PET film (PET) substrate 21 can be used, and the X-ray transmittance is increased.

(Embodiment 4) FIG. 5 is a schematic sectional view of an X-ray detector according to Embodiment 4 of the present invention. X shown in FIG.
The X-ray detector detects the Pb glass substrate 19 with the sensor substrate 11
The manufacturing steps are the same as those in the first embodiment until they are attached with an epoxy adhesive or the like. After this, the sensor substrate 11
Polished to make it thinner.

As described in the first embodiment, the thickness of the sensor substrate 11 is determined in consideration of making the sensor substrate 11 hard to crack in the manufacturing process of the X-ray detector. Therefore, it is not necessary to make the sensor substrate 11 thick after the Pb glass substrate 19 side and the sensor substrate 11 are attached to each other. Therefore, in the subsequent steps, the sensor substrate 11 is thinned to suppress the absorption of radiation here, and to improve the light receiving sensitivity and the MTF.

(Embodiment 5) FIG. 6 is a schematic sectional view of an X-ray detector according to Embodiment 5 of the present invention. X shown in FIG.
The X-ray detector detects the Pb glass substrate 19 with the sensor substrate 11
The manufacturing process is the same as that of the first embodiment up to the step of attaching with an epoxy adhesive or the like. Thereafter, the sensor substrate 11 is etched.

FIG. 6A shows that the entire surface of the sensor substrate 11 is etched back by, for example, dry etching without patterning. The etched portion 24 is shown. FIG. 6B shows a case where only the photoelectric conversion portion (not shown) on the sensor substrate 11 is etched after patterning the resist 25 on the portion to be etched 24 using photolithography technology, laser technology, or the like.

In this embodiment, the sensor substrate 11 on the photoelectric conversion unit is formed by dry etching after patterning.
Was etched. It is also possible to use wet etching. By making the sensor substrate 11 thin, absorption of radiation by the sensor substrate 11 can be suppressed, and light receiving sensitivity and MTF can be improved.

[0032]

As described above, according to the present invention,
Since the radiation is converted into light at the scintillator layer near the photoelectric conversion unit, which is incident from the sensor substrate side, the radiation does not attenuate before reaching the photoelectric conversion unit, and the light receiving sensitivity and M
TF can be improved. Further, by reducing the thickness of the glass substrate, absorption of radiation in the substrate can be suppressed, and high sensitivity can be achieved.

Further, since the Pb glass substrate also functions as an X-ray shielding plate, a lead plate (X-ray shielding plate) for protecting the memory in the processing circuit from X-rays is not required. Thereby, the configuration of the X-ray detection device is simplified, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an X-ray detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a relative light emission amount and a modulation transfer function (MTF) with respect to a difference in thickness of a scintillator layer in FIG. 1;

FIG. 3 is a schematic sectional view of an X-ray detection device according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of an X-ray detection device according to a third embodiment of the present invention.

FIG. 5 is a schematic sectional view of an X-ray detection device according to a fourth embodiment of the present invention.

FIG. 6 is a schematic sectional view of an X-ray detector according to Embodiment 5 of the present invention.

FIG. 7 is a schematic sectional view of a conventional X-ray detection device.

FIG. 8 is an equivalent circuit diagram near the sensor unit of FIG. 7;

FIG. 9 is a sectional view of the PIN photodiode and the TFT of FIG. 8;

FIG. 10 is a diagram showing the relationship between the thickness of a scintillator layer and MTF.

FIG. 11 is a diagram showing a relationship between a distance from an optical axis of light changed by a scintillator layer and a light emission amount.

[Explanation of symbols]

 Reference Signs List 11 sensor substrate 14 SiN protective film 15 X-ray 16 scintillator layer 18 Al layer 19 Pb glass substrate 20 stainless steel plate 21 pet film substrate 22 roller 25 resist

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2G088 EE01 EE27 FF02 FF14 GG10 GG16 GG19 GG20 JJ05 JJ09 JJ29 JJ37 LL08 LL12 LL15 4M118 AA10 AB10 BA05 CA05 CA32 CB11 EA01 FB08 FB09 FB13 GA04 AB05 GA03F

Claims (6)

[Claims] 1. A radiation detecting apparatus having a scintillator formed on a sensor substrate having at least a plurality of photoelectric conversion elements, wherein a radiation shield is formed on the scintillator, and radiation is incident from the sensor substrate side. Radiation detection device. 2. The radiation detection apparatus according to claim 1, wherein the radiation shield is made of a metal-containing material having a thickness and an absorptivity so that the radiation does not leak to the outside. 3. The scintillator comprises cesium iodide,
The radiation detection apparatus according to claim 1, wherein one of GOS, amorphous selenium, PbI ₂ , and HgI ₂ is used. 4. The radiation detecting apparatus according to claim 1, wherein the sensor base is an organic base. 5. The radiation detecting apparatus according to claim 1, wherein the sensor base has a thickness that allows the radiation to sufficiently reach the scintillator. 6. The radiation detecting apparatus according to claim 1, wherein a portion of the sensor base on the photoelectric conversion element is thinner than other portions.