JP2004239722A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiating detector which can improve resolution, mechanical strength and intensity unevenness of a pixel. <P>SOLUTION: The radiating detector is provided with a photoelectric conversion substrate 11 in which a plurality of photoelectric conversion elements 13 of a pixel unit are arranged, a scintillator layer 39 arranged on the substrate 11, and compartment 38 which is formed on the substrate 11 and partitions the scintillator layer 39 per pixel, The scintillator layer 39 includes a first scintillator layer 391 on the substrate 11, and a second scintillator layer 392 on the first scintillator layer 391, The first scintillator layer 391 is arranged between the substrate 11 and the compartment 38. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radiation detector, and more particularly, to an indirect radiation detector that detects a radiation image.
[0002]
[Prior art]
Active matrix type flat panel detectors have attracted much attention as new generation X-ray diagnostic detectors. By detecting the irradiated X-rays in this plane detector, an X-ray photographed image or a real-time X-ray image is output as a digital signal. Because it is a solid-state detector, expectations are extremely high in terms of image quality and stability. For this reason, many universities and manufacturers are engaged in R & D.
[0003]
As the first application for practical use, it has been developed for chest and general radiography for collecting still images with a relatively large X-ray dose, and has been commercialized in recent years. Commercialization is expected in the near future for applications in the cardiovascular and gastrointestinal fields, which need to clear higher technical hurdles and realize real-time video of 30 frames per second or more under fluoroscopic dose. . For this moving image application, improvement of S / N and real-time processing technology of minute signals are important development items.
[0004]
Flat detectors are roughly classified into two types: a direct type and an indirect type.
[0005]
The direct method is a method in which X-rays are directly converted into signal charges using a photoconductive film such as a-Se, and the converted signal charges are stored in a charge storage capacitor. In this direct method, photoconductive charges generated by X-rays are directly led to a charge storage capacitor by a high electric field, so that a resolution characteristic substantially defined by a pixel pitch of an active matrix can be obtained.
[0006]
On the other hand, the indirect method is a method in which X-rays are received by a scintillator layer and temporarily converted into visible light, the visible light is converted into signal charges by an a-Si photodiode or a CCD, and is guided to a charge storage capacitor. In the indirect method, the resolution is deteriorated by the optical diffusion and scattering of the visible light from the scintillator layer until it reaches the photodiode.
[0007]
However, in this indirect method, by separating the scintillator layer for each pixel by the partition, the fluorescent light emitted in the scintillator layer is suppressed from being scattered or diffused in the lateral direction by the partition. Therefore, the fluorescence can efficiently reach the photoelectric conversion element such as the photodiode by the optical guiding effect, and the resolution characteristic is improved (for example, see Patent Document 1).
[0008]
In addition, the technology for the scintillator material and the photo diode is established, and it is possible to stably produce the material compared to the direct method.
[0009]
[Patent Document 1]
JP-A-11-166976
[0010]
[Problems to be solved by the invention]
In the above-described method for manufacturing a pixel separation type scintillator, for example, a scintillator layer is formed on a photoelectric conversion substrate in which a plurality of photoelectric conversion elements are arranged. Thereafter, a groove is formed in the scintillator layer to perform pixel separation. Then, the partition is formed by filling the inside of the groove with a light reflecting material.
[0011]
From the viewpoint of resolution characteristics, it is preferable that the groove is formed at a depth reaching the photoelectric conversion substrate, and the scintillator layer is completely separated into pixels.
[0012]
In such a structure, the mechanical strength δ of the scintillator layer is determined by the contact area S between the scintillator layer and the insulating layer for protecting the photodiode. _F And the adhesive strength γ between them _F (Δ = S _F × γ _F ) Depends. However, the contact area S _F Is very small and the adhesive strength γ _F Is also very weak because of the adhesive strength between different substances. For this reason, the mechanical strength δ of the scintillator layer is extremely weak, and the probability of occurrence of side-down or jump of the scintillator layer (so-called chip jump) increases.
[0013]
When pixel separation is completely performed, the luminance of each pixel greatly depends on the volume of the scintillator layer formed on each photoelectric conversion element and the packing density of the phosphor particles constituting the scintillator layer. For example, a slight difference in the volume of the scintillator layer between the pixels causes a difference in luminance between the pixels. This phenomenon is a major factor for uneven brightness of an image.
[0014]
The present invention has been made in view of the above-described problems, and has as its object to provide a radiation detector capable of improving resolution and mechanical strength and improving luminance unevenness of pixels. Is to provide.
[0015]
[Means for Solving the Problems]
The radiation detector according to the first aspect of the present invention includes:
A photoelectric conversion substrate in which a plurality of pixel-based photoelectric conversion elements are arranged,
A scintillator layer disposed on the photoelectric conversion substrate,
A partition portion formed on the photoelectric conversion substrate and partitioning the scintillator layer in pixel units;
With
The scintillator layer includes a first scintillator layer on the photoelectric conversion substrate, and a second scintillator layer on the first scintillator layer,
The first scintillator layer is disposed between the photoelectric conversion substrate and the partition.
[0016]
The radiation detector according to the second aspect of the present invention includes:
A photoelectric conversion substrate in which a plurality of pixel-based photoelectric conversion elements are arranged,
A scintillator layer disposed on the photoelectric conversion substrate,
A partition portion formed on the photoelectric conversion substrate and partitioning the scintillator layer in pixel units;
With
The scintillator layer includes a first scintillator layer disposed on the photoelectric conversion substrate and formed of phosphor particles having a first average particle diameter D1; and a first scintillator layer disposed on the first scintillator layer. A second scintillator layer composed of phosphor particles having a larger second average particle diameter D2.
At least the first scintillator layer is disposed between the photoelectric conversion substrate and the partition.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a radiation detector according to an embodiment of the present invention will be described with reference to the drawings.
[0018]
The present invention is applicable to the case of X-rays, γ-rays, and other various types of radiation. However, in the following embodiment, a case of a typical X-ray among the radiations will be described as an example. Therefore, by replacing “X-ray” in the embodiment with “radiation”, the present invention can be applied to other radiations targeted by the present invention.
[0019]
As shown in FIG. 1, an X-ray detector 1 that detects an X-ray and outputs an electric signal corresponding to the intensity distribution of the X-ray has an active matrix type photoelectric conversion substrate 11 having a plurality of pixels. I have. The photoelectric conversion substrates 11 are two-dimensionally arranged in a matrix at a predetermined pitch L in a row direction (for example, a horizontal direction in the drawing) and a column direction (for example, a vertical direction in the drawing) on an insulating substrate such as glass. A plurality of pixels 12 having the same structure. In the example shown in FIG. 1, nine pixel units (12a to 12i) are illustrated.
[0020]
Each of the pixels 12 (a to i) includes a photodiode 13 functioning as a photoelectric conversion element that converts the signal charge into incident signal light intensity, a thin film transistor (hereinafter, referred to as a TFT) 14 functioning as a switching element, and a signal charge. It is composed of a storage capacitor 15 functioning as a charge storage unit for storing.
[0021]
Each TFT 14 has a gate electrode G, a source electrode S, and a drain electrode D. The drain electrode D is electrically connected to, for example, the photodiode 13 and the storage capacitor 15.
[0022]
A control circuit 16 is provided outside the photoelectric conversion substrate 11. The control circuit 16 controls the operation state of the TFT 14, for example, on / off. The control circuit 16 is connected to a plurality of control lines 17 extending in the row direction. In the example shown in FIG. 1, first to fourth four control lines 171 to 174 are provided. Each control line 17 is connected to a gate electrode G of each TFT 14 constituting the pixels 12 in the same row. For example, the first control line 171 is connected to the gate electrode G of each TFT 14 forming the pixels 12a to 12c.
[0023]
A plurality of data lines 18 are provided in the column direction. In the example shown in FIG. 1, first to fourth four data lines 181 to 184 are provided. Each data line 18 is connected to the source electrode S of each TFT 14 constituting the pixels 12 in the same column. For example, the first data line 181 is connected to the source electrode S of each TFT 14 forming the pixels 12a, 12d, and 12g.
[0024]
Each data line 17 is connected to a corresponding charge amplifier 19. Each charge amplifier 19 is composed of, for example, an operational amplifier. The data line 18 is connected to one input terminal a1, and the other input terminal a2 is grounded. A capacitor C is connected between one input terminal a1 and the output terminal b, and has an integrating function. Further, a switch S is connected in parallel with the capacitor C. For example, the switch S is closed to discharge the charge remaining in the capacitor C.
[0025]
Each charge amplifier 19 is connected to a parallel / serial converter 20 that converts a plurality of electric signals input in parallel into serial signals. The parallel / serial converter 20 is connected to an analog-digital converter 21 that converts an analog signal into a digital signal.
[0026]
(1st Embodiment)
Next, a structure of a pixel unit of the X-ray detector according to the first embodiment will be described with reference to FIG. In FIG. 2, one pixel portion is extracted and shown, and portions corresponding to FIG. 1 are denoted by the same reference numerals, and a duplicate description is partially omitted.
[0027]
The photoelectric conversion substrate 11 includes a TFT 14 and a storage capacitor 15 formed on an insulating substrate 31 such as glass.
[0028]
The TFT 14 has three electrical connections, that is, a gate electrode G, a source electrode S, and a drain electrode D. The gate electrode G is formed on the insulating substrate 31. The gate electrode G is covered with the insulating film 32. The gate electrode G is connected to a common control line 17 together with the gate electrodes G of the other TFTs 14 located on the same row.
[0029]
The source electrode S is in contact with a semi-insulating film 33 formed on the insulating film 32. The source electrode S is connected to a common data line 18 together with the source electrodes S of other TFTs 14 located in the same column. The drain electrode D is in contact with the semi-insulating film 33. The drain electrode D is connected to the photodiode 13 and the storage capacitor 15.
[0030]
The storage capacitor 15 includes a lower electrode 34 formed on the insulating substrate 31, an upper electrode 35 provided to face the lower electrode 34 with the insulating film 32 interposed therebetween, and the like. The upper electrode 35 is electrically connected to the drain electrode D of the TFT 14.
[0031]
A first insulating layer 361 is provided above the TFT 14 and the storage capacitor 15. The photodiode 13 is formed on the first insulating layer 361. On the first insulating layer 361 around the photodiode 13, a second insulating layer 362 is provided. The second insulating layer 362 is formed in a frame shape so as to surround the photodiode 13 having a substantially rectangular shape.
[0032]
The photodiode 13 is formed of an a-Si pn diode, a PIN diode, or the like. The photodiode 13 includes a first electrode 131 formed on the first insulating layer 361, a second electrode 132 disposed to face the first electrode 131, and the like.
[0033]
The first electrode 131 is connected to the drain electrode D of the TFT 14 via a through hole 37 formed in a part of the first insulating layer 361. The second electrode 132 is formed, for example, by forming a transparent conductive film such as ITO by a sputtering method. A bias voltage is applied between the first electrode 131 and the second electrode 132.
[0034]
A scintillator layer 39 that converts X-rays incident from the outside into visible light is disposed on the photoelectric conversion substrate 11 having the above-described structure. Further, on the photoelectric conversion substrate 11, a partitioning section 38 for partitioning the scintillator layer 39 in pixel units is formed. The partition 38 is constituted by, for example, a partition or a groove.
[0035]
That is, as shown in FIG. 2, the scintillator layer 39 is disposed on the photodiode 13 and the second insulating layer 362 on the photoelectric conversion substrate 11. This scintillator layer 39 is made of phosphor particles having substantially the same average particle diameter, for example, GOS (Gd ₂ O ₂ S: Tb, PR ⁺³ , CE ⁺³ , F). The particle size of the phosphor particles constituting the scintillator layer 39 is confirmed by, for example, photographing a cross section of the scintillator layer 39 with a scanning electron microscope.
[0036]
This scintillator layer 39 is formed, for example, by the following method. First, a scintillator-containing coating layer is formed by applying a liquid scintillator material on a photoelectric conversion substrate 11 having a plurality of photodiodes 13 arranged in a matrix. This scintillator material is, for example, Gd as phosphor particles that absorb X-rays and emit light. ₂ O ₂ S: A powder of Tb is formed using a resin binder and an organic solvent. This scintillator material is applied by a coating method using a dispenser, ink jet, spray, or the like.
[0037]
Thereafter, the organic solvent is removed through a drying step of heating at 60 to 150 ° C., and the scintillator-containing coating layer is cured. As a result, a good scintillator layer 39 that does not cause peeling or cracking of the film is formed.
[0038]
The partitioning section 38 converts the X-rays 40 incident on the scintillator layer 39 from above into fluorescent light 41 in the scintillator layer 39, and prevents the fluorescent light 41 from interfering with the area of the photodiode 13 of the adjacent pixel 12. Are formed along the boundaries that separate
[0039]
The partition 38 is formed, for example, by the following method. First, a groove is formed in the scintillator layer 39. Then, as a light reflecting material having high refraction characteristics, for example, TiO ₂ Or as X-ray emitting phosphor particles such as Gd ₂ O ₂ S: A partition is formed by filling with Tb. In addition, even if only the groove is formed without forming the partition, the function as the partition 38 is provided.
[0040]
The above-mentioned grooves can be formed by using a dicer or an ultraviolet laser of the third harmonic of YAG. This groove is formed to such a depth that a part of the scintillator layer 39 remains without reaching the photoelectric conversion substrate 11. That is, the scintillator layer 39 exists between the photoelectric conversion substrate 11 and the partition 38.
[0041]
In the first embodiment, the scintillator layer 39 existing between the photoelectric conversion substrate 11 and the partition 38 is referred to as a first scintillator layer 391 for convenience of explanation. That is, the scintillator layer 39 includes a first scintillator layer 391 disposed on the photoelectric conversion substrate 11 and a second scintillator layer 392 disposed on the first scintillator layer 391. Naturally, the first scintillator layer 391 is made of phosphor particles having an average particle diameter substantially equal to that of the second scintillator layer 392.
[0042]
The first scintillator layer 391 shown in FIG. 2 has an integrated structure connected to the first scintillator layer 391 of the adjacent pixel 12. That is, the first scintillator layer 391 is not partitioned into pixel units by the partitioning section 38 but is disposed between the photoelectric conversion substrate 11 and the partitioning section 38. On the other hand, the second scintillator layer 392 is partitioned by the partitioning unit 38 into pixel units.
[0043]
It is desirable that the average thickness T1 of the first scintillator layer 391 be equal to or larger than the average particle diameter D1 of the phosphor particles constituting the first scintillator layer 391. Thereby, the mechanical strength of the scintillator layer 39 can be improved.
[0044]
That is, the mechanical strength δ of the scintillator layer 39 is determined by the contact area S between the scintillator layer 39 and the second insulating layer 362 for protecting the photodiode 13. _F And the adhesive strength γ between them _F (Δ = S _F × γ _F ) Depends. When the partitioning section 38 performs complete pixel separation reaching the photoelectric conversion substrate 11, the contact area S _F Is very small and the adhesive strength γ _F Also very weak. For this reason, the mechanical strength δ is extremely weak, and the probability of occurrence of the lateral fall of the scintillator layer 39 and the jump of the scintillator (so-called chip jump) increases.
[0045]
However, as in the above-described first embodiment, the first scintillator layer 391 is disposed below the partition 38 without the partition 38 reaching the photoelectric conversion substrate 11. Can be connected via the first scintillator layer 391, and the mechanical strength δ of the scintillator layer 39 in pixel units can be improved.
[0046]
That is, the mechanical strength δ in the structure shown in FIG. 2 is equal to the contact area S between the scintillator layer 39 and the second insulating layer 362 for protecting the photodiode 13. _F And the adhesive strength γ between them _F And the contact area S between the scintillator layer 39 on the photodiode 13 and the scintillator layer 39 located below the partition 38. _S And the adhesive strength γ between them _S (Δ = S _F × γ _F + S _S × γ _S ).
[0047]
Adhesion strength γ between scintillator layers formed of the same type of material _S Is very strong. Therefore, the contact area S between the scintillator layers is _S Is small, that is, if the scintillator layer 39 exists even slightly below the partition 38, the mechanical strength δ of the scintillator layer 39 is significantly improved.
[0048]
Further, as the average film thickness T of the scintillator layer 39 located below the partitioning section 38 increases, the contact area S between the scintillator layers 39 increases. _S Is increased, so that the mechanical strength δ is improved.
[0049]
Further, by providing continuity between the scintillator layers 39 of the pixels 12 adjacent to each other through the first scintillator layer 391, local peeling and lateral falling of the pixels 12 can be suppressed by reinforcing each other with adjacent pixels. For this reason, the probability of occurrence of chip jump can be significantly reduced.
[0050]
FIG. 3 shows an example of the relationship between the average thickness T1 of the first scintillator layer 391 and the number of chip jumps. At this time, the average particle size D1 of the phosphor particles constituting the scintillator layer 39 is 40 μm. The number of chip jumps corresponds to the number of pixels in which chip jumps occur in the pixels 12 located within a 1 cm square.
[0051]
As is clear from the results shown in FIG. 3, the larger the average thickness T1 of the first scintillator layer 391 located below the partition portion 38, the more the number of chip jumps can be significantly reduced. In the example shown in FIG. 3, the number of chip jumps is significantly reduced by setting the average thickness T1 of the first scintillator layer 391 to be equal to or larger than the average particle diameter D1 of phosphor particles (40 μm in this example). be able to.
[0052]
Conversely, when the average thickness T1 of the first scintillator layer 391 is smaller than the particle diameter D1 of the phosphor particles constituting the first scintillator layer 391, grooves are formed in the phosphor particles constituting the first scintillator layer 391. Will do. In this case, the probability of cracks occurring in the phosphor particles is very high. When the cracks occur in the phosphor particles, the continuity of the scintillator layer 39 between adjacent pixels 12 is lost, and the mechanical strength δ of the scintillator layer 39 becomes very weak. For this reason, the number of chip jumps cannot be reduced sufficiently.
[0053]
Therefore, it is preferable that the average thickness T1 of the first scintillator layer 391 be equal to or larger than the particle diameter D1 of the phosphor particles constituting the first scintillator layer 391.
[0054]
Further, with the structure as shown in FIG. 2, the fluorescent light 41 that travels through the second scintillator layer 392 separated by the pixel by the light guide effect makes the first scintillator layer 39 having continuity between the scintillator layers 39 of the adjacent pixels 12. Upon reaching 391, the fluorescent light 14 is scattered, and some fluorescent light 14 reaches the photodiode 13 of the adjacent pixel.
[0055]
With this effect, the luminance of the adjacent pixels 12 is averaged, and the luminance unevenness of the image is improved. For example, when the pixel 12 having a low luminance characteristic and the pixel 12 having a high luminance characteristic are adjacent to each other due to a difference in the packing density of the phosphor particles in each pixel 12, the pixel having the low luminance is shifted from the pixel having the high luminance through the first scintillator layer 391. Obviously, the amount of fluorescent light diffused to the side exceeds the amount of fluorescent light in the opposite direction. Similar effects can be expected when adjacent pixels are arranged one-dimensionally like a line sensor or two-dimensionally like a plane detector.
[0056]
As described above, when the adjacent pixels 12 are optically connected to each other through the first scintillator layer 391, there is an effect of complementing the luminance between the nearest pixels 12. For this reason, the effect of suppressing luminance unevenness is exhibited. This effect also increases as the average thickness T1 of the first scintillator layer 391 increases.
[0057]
On the other hand, it is desirable that the average thickness T of the first scintillator layer 391 is 110 μm or less. Thereby, it is possible to improve the resolution as the X-ray flat panel detector.
[0058]
FIG. 4 shows an example of the relationship between the average thickness T1 of the first scintillator layer 391 and its resolution characteristic CTF. As shown in FIG. 4, as the average thickness T1 of the first scintillator layer 391 located below the partitioning section 38 increases, the resolution characteristics deteriorate.
[0059]
That is, the fluorescent light 41 generated in the scintillator layer 39 diffuses into the scintillator layer 39 of the adjacent pixel 12 via the first scintillator layer 391 as the average film thickness T1 increases. For this reason, the fluorescence of the adjacent pixel 12 reaches the photodiode 13 of the predetermined pixel 12 excessively, and the resolution characteristic deteriorates.
[0060]
As a resolution characteristic of the X-ray flat panel detector, a characteristic higher than the input surface of the image tube (II) used for the X-ray diagnostic detector is required. The resolution characteristic CTF of the input surface of the image tube is 35% or more at 2 lp / mm. Referring to the results shown in FIG. 4, it is desirable that the average thickness T of the first scintillator layer 391 be 110 μm or less so that the resolution characteristic CTF is 35% or more. This makes it possible to obtain a good resolution.
[0061]
As described above, according to the X-ray detector according to the first embodiment, the scintillator layer 39 is partitioned on a pixel-by-pixel basis by the partition 38 formed by the partition or the groove. The scintillator layer 39 is composed of a first scintillator layer 391 disposed between the photoelectric conversion substrate 11 and the partitioning section 38, and substantially the same material as the first scintillator layer 391 disposed on the first scintillator layer 391. And a second scintillator layer 392 composed of
[0062]
The first scintillator layer 391 has an integral structure common to adjacent pixels. Therefore, the contact area between the scintillator layer 39 and the insulating layer 362 can be increased, and the mechanical strength of the scintillator layer 39 can be improved. In addition, the second scintillator layer 392 is partitioned by the partitioning unit 38 into pixel units. Therefore, the pixels can be separated by partitioning the scintillator layer 39, and the resolution can be improved.
[0063]
The average thickness T1 of the first scintillator layer 391 is set to be equal to or larger than the particle diameter D1 of the phosphor particles constituting the first scintillator layer 391. Thereby, the mechanical strength of the scintillator layer 39 in which the pixels are separated can be improved, and the luminance unevenness of the image can be reduced.
[0064]
Further, the average thickness T1 of the first scintillator layer 391 is set to 110 μm or less. Thus, the scintillator layer 39 can be separated into pixels by the partitioning section 38 (particularly, the second scintillator layer 392 can be partitioned by the partitioning section 38 in pixel units), and the resolution can be improved.
[0065]
(2nd Embodiment)
Next, a structure of a pixel unit of the X-ray detector according to the second embodiment will be described with reference to FIG. In FIG. 5, one pixel portion is extracted and shown, and portions corresponding to FIG. 1 and FIG. 2 are denoted by the same reference numerals, and redundant description is partially omitted.
[0066]
The resolution of the indirect X-ray detector affects the efficiency of the fluorescence until the scintillator layer receives the X-rays, converts the X-rays into fluorescence, and reaches the photodiode. In order to efficiently guide the fluorescence to the photodiode, it is desirable that the ratio of the interface between the phosphor particles and the surrounding binder and the like occupying the same volume of the scintillator layer is as small as possible. That is, it is desirable that the particle size of the phosphor particles is large.
[0067]
However, when the scintillator layer is formed of phosphor particles having a relatively large particle size, the scintillator layer located below the partitioning portion also efficiently guides fluorescence, so that the fluorescence of another pixel is applied to the photodiode of the adjacent pixel. There is a risk of intrusion, and the resolution may be degraded.
[0068]
Therefore, the second embodiment is to provide an X-ray detector capable of efficiently guiding the fluorescence generated in the scintillator layer to the photodiode and improving the resolution.
[0069]
That is, as shown in FIG. 5, the X-ray detector according to the second embodiment includes a scintillator layer 39 disposed on the photoelectric conversion substrate 11 and a scintillator layer 39 formed on the photoelectric conversion substrate 11 in pixel units. And a partitioning section 38 for partitioning. This scintillator layer 39 is arranged on the photodiode 13 and the second insulating layer 362 in the photoelectric conversion substrate 11.
[0070]
The scintillator layer 39 includes a first scintillator layer 391 formed on the photoelectric conversion substrate 11 and formed of phosphor particles having a first average particle diameter D1, and a first scintillator layer 391 disposed on the first scintillator layer 391. A second scintillator layer 392 made of phosphor particles having a second average particle diameter D2 larger than the diameter D1.
[0071]
This scintillator layer 39 is formed, for example, by the following method. First, a liquid first scintillator material is applied on a photoelectric conversion substrate 11 having a plurality of photodiodes 13 and the like arranged in a matrix to form a first scintillator-containing coating layer. The first scintillator material is, for example, Gd as a phosphor particle having a first average particle diameter D1 that absorbs and emits X-rays. ₂ O ₂ S: A powder of Tb is formed using a resin binder and an organic solvent.
[0072]
Thereafter, the organic solvent is removed through a drying step of heating at 60 to 150 ° C., and the first scintillator-containing coating layer is cured. As a result, a favorable first scintillator layer 391 that does not cause peeling or cracking of the film is formed.
[0073]
Subsequently, a liquid second scintillator material is applied on the first scintillator layer 391 to form a second scintillator-containing coating film layer. This second scintillator material is, for example, Gd as phosphor particles having a second average particle diameter D2 larger than the first average particle diameter D1 that absorbs and emits X-rays. ₂ O ₂ S: A powder of Tb is formed using a resin binder and an organic solvent.
[0074]
These first and second scintillator materials are applied by a coating method using a dispenser, an inkjet, a spray, or the like.
[0075]
Thereafter, the organic solvent is removed through a drying step of heating at 60 to 150 ° C., and the second scintillator-containing coating layer is cured. As a result, a favorable second scintillator layer 392 that does not cause film peeling or cracking is formed.
[0076]
The partitioning section 38 converts the X-rays 40 incident on the scintillator layer 39 from above into fluorescent light 41 in the scintillator layer 39, and prevents the fluorescent light 41 from interfering with the area of the photodiode 13 of the adjacent pixel 12. Are formed along the boundaries that separate
[0077]
The partition 38 is formed in the same manner as in the first embodiment. The partitioning portion 38 including the groove and the partition formed in the groove is formed to such a depth that a part of the scintillator layer 39 remains without reaching the photoelectric conversion substrate 11. That is, the scintillator layer 39 exists between the photoelectric conversion substrate 11 and the partition 38. At least a first scintillator layer 391 is arranged between the photoelectric conversion substrate 11 and the partitioning section 38.
[0078]
The first scintillator layer 391 shown in FIG. 5 has an integrated structure connected to the first scintillator layer 391 of the adjacent pixel 12. That is, the first scintillator layer 391 is not partitioned into pixel units by the partitioning section 38 but is disposed between the photoelectric conversion substrate 11 and the partitioning section 38.
[0079]
On the other hand, most of the second scintillator layer 392 is partitioned by the partitioning section 38 into pixel units. Since the second scintillator layer 392 is composed of phosphor particles having a relatively large average particle diameter, the second scintillator layer 392 efficiently guides the fluorescent light 41 generated by X-ray incidence in the vertical direction (downward) toward the photodiode 13. Can be. In addition, since most of the second scintillator layer 392 is partitioned by the partition 38, the scattering and diffusion of the fluorescent light 41 generated in the second scintillator layer 392 to adjacent pixels is suppressed. be able to.
[0080]
The fluorescent light 14 generated in the scintillator layer 39 is scattered and attenuated by refraction at the interface between the phosphor particles and the binder around the phosphor particles. In order to suppress the attenuation of the fluorescent light 14 and efficiently guide the fluorescent light 14 to the photodiode, the ratio of the interface between the phosphor particles and the surrounding binder and the like occupying the same volume of the scintillator layer 39 is minimized, that is, the phosphor The larger the average particle size of the particles, the better.
[0081]
However, when the scintillator layer 39 located below the partitioning portion 38 is made of a phosphor particle having a relatively large particle size, the fluorescence 41 is diffused without being greatly attenuated here, and is diffused to the photodiode 13 of the adjacent pixel 12. There is a possibility that the fluorescence of the other pixels 12 will reach and the resolution will be degraded.
[0082]
Therefore, it is necessary to suppress the diffusion of the emitted fluorescent light 41 in the scintillator layer 39 located below the partitioning section 38 and in the scintillator layer 39 in contact with the photodiode 13. That is, in the scintillator layer 39 located below the partition 38 and the scintillator layer 39 in contact with the photodiode 13, the ratio of the interface between the phosphor particles and the binder around the phosphor particles is maximized, that is, the average particle size of the phosphor particles is increased. The smaller the diameter, the better.
[0083]
FIG. 6 shows an example of the relationship between the average particle size of the phosphor particles constituting the scintillator layer 39 and its resolution characteristic CTF. Here, the scintillator layer 39 has a thickness of 100 μm, and is formed of phosphor particles having a substantially uniform particle size. As is clear from the results shown in FIG. 6, the smaller the average particle size of the phosphor particles constituting the scintillator layer 39, the more the resolution characteristics CTF can be improved.
[0084]
Therefore, as shown in FIG. 5, the scintillator layer 39 has a two-layer structure having different average particle sizes. The second scintillator layer 392 located on the X-ray incidence side is made of phosphor particles having a relatively large average particle diameter D2. The first scintillator layer 391 located on the photodiode 13 is composed of phosphor particles having a relatively small average particle diameter D1.
[0085]
That is, the relationship between the average particle diameter D1 of the phosphor particles constituting the first scintillator layer 391 and the average particle diameter D2 of the phosphor particles constituting the second scintillator layer 392 is D1 <D2. It is desirable that the difference between the two is large.
[0086]
Accordingly, the second scintillator layer 392 can suppress the attenuation of the fluorescent light 41 generated by the incidence of the X-rays and efficiently guide the fluorescent light 41 downward. In addition, the first scintillator layer 391 can guide the fluorescence 41 generated in the second scintillator layer 392 to the photodiode 13 and suppress diffusion to the adjacent pixels 12, thereby suppressing a reduction in resolution.
[0087]
Note that the average thickness T1 of the first scintillator layer 391 is desirably equal to or less than the interval t2 between the photoelectric conversion substrate 11 and the partition 38. That is, if the average thickness T1 of the first scintillator layer 391 in contact with the photodiode 13 is too large, the first scintillator layer 391 itself becomes a reflective film because the first average particle diameter D1 of the first scintillator layer 391 is relatively small. It acts to reflect the fluorescent light 41 emitted from the second scintillator layer 392.
[0088]
Therefore, in order to reduce the influence of reflection at the boundary between these two scintillator layers 391 and 392, the average thickness T1 of the first scintillator layer 391 needs to be as small as possible. It is necessary that the thickness of the scintillator layer 39 be between 38 and 38 or less.
[0089]
It is desirable that the partition 38 be formed to a depth reaching the boundary between the two scintillator layers 391 and 392 (that is, T1 = T2). Such a structure makes it possible to completely separate the pixels of the second scintillator layer 392 that efficiently diffuses the fluorescent light 41 by the partition portion 38, and to diffuse the fluorescent light 41 in the first scintillator layer 391 that is not separated by the pixel. Can be suppressed. Thereby, the resolution characteristics as an X-ray detector can be improved.
[0090]
Even when the partitioning portion 38 does not reach the boundary between the two scintillator layers 391 and 392 (T1 <T2), the resolution effect of the X-ray detector is improved by the above-described effect, although not as much as when T1 = T2. be able to.
[0091]
On the other hand, the first average particle size of the phosphor particles constituting the first scintillator layer 391 is D1, the average film thickness of the first scintillator layer 391 is T1, and the average filling rate of the phosphor particles in the first scintillator layer 391 is Assuming F1,
D1 ≧ T1 · F1 / 10
It is desirable to have the relationship of
[0092]
That is, FIG. 7 shows an example of the relationship between the number of phosphor particles constituting the scintillator layer in the thickness direction and the transmittance of the fluorescence passing through the scintillator layer. As is clear from the results shown in FIG. 7, in order for the fluorescence of 10% or more to reach from the upper part to the lower part of the scintillator layer, the thickness of the phosphor particles is preferably 10 layers or less. By the average packing density F1 of the particles and the effective film thickness T1 · F1,
T1 · F1 / D1 ≦ 10
It is desirable that the relationship be
[0093]
As described above, according to the X-ray detector according to the second embodiment, the scintillator layer 39 has a two-layer structure, and is formed on the photoelectric conversion element substrate 11 by the phosphor particles having the first average particle diameter D1. A first scintillator layer 391 is arranged, and a second scintillator layer 392 made of phosphor particles having a second average particle diameter D2 larger than the first average particle diameter D1 is arranged on the first scintillator layer 391. .
[0094]
Thereby, the attenuation of the fluorescent light 41 emitted by the second scintillator layer 392 is suppressed, and the fluorescent light 41 can be efficiently guided in the vertical direction. In addition, diffusion of the fluorescent light 41 guided from the second scintillator layer 392 to the first scintillator layer 391 is suppressed, and a reduction in resolution can be prevented.
[0095]
Further, the average thickness T1 of the first scintillator layer 391 is set to be equal to or less than the interval T2 between the photoelectric conversion substrate 11 and the partition 38. Thereby, the second scintillator layer 392 is separated into pixels by the partitioning portion 38, so that the resolution can be improved.
[0096]
Further, the first average particle diameter of the phosphor particles constituting the first scintillator layer 391 is D1, the average film thickness of the first scintillator layer 391 is T1, and the average filling rate of the phosphor particles in the first scintillator layer 391 is F1. And when
D1 ≧ T1 · F1 / 10
And relationship. Thereby, the transmittance of the fluorescence reaching the photodiode 13 from the scintillator layer can be sufficiently ensured.
[0097]
In the above-described embodiment, as shown in FIG. 8, the X-rays 40 are radiated radially by the X-ray source 51 installed at a distance from the center of the scintillator layer 39 to the upper surface. For this reason, it is desirable that the partitioning section 38 for separating the pixels of the scintillator layer 39 be formed so as to be parallel to the traveling direction of the normal X-ray (straight wave) emitted from the X-ray source 51.
[0098]
The present invention is not limited to the above embodiments, and various modifications and changes can be made at the stage of implementation without departing from the scope of the invention. In addition, the embodiments may be implemented in appropriate combinations as much as possible, and in that case, the effect of the combination is obtained.
[0099]
Although the radiation detector according to the present invention has been described with respect to a configuration in which a plurality of pixels are arranged vertically and horizontally, the ratio of the pixels vertically and horizontally is different (for example, when one of the pixels is one, etc.), it looks linear at first glance. It is also possible to apply to the X detector configured as described above. In this case, the switching element can be implemented without using a TFT.
[0100]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a radiation detector capable of improving resolution and mechanical strength and improving luminance unevenness of pixels.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a circuit configuration of an X-ray detector according to one embodiment of the present invention.
FIG. 2 is a sectional view schematically showing a structure of one pixel portion of the X-ray detector according to the first embodiment.
FIG. 3 is a diagram illustrating an example of a relationship between an average film thickness of a first scintillator layer and the number of chip jumps.
FIG. 4 is a diagram illustrating an example of a relationship between an average film thickness of a first scintillator layer and resolution characteristics thereof.
FIG. 5 is a sectional view schematically showing a structure of one pixel portion of an X-ray detector according to a second embodiment.
FIG. 6 is a diagram showing an example of a relationship between an average particle size of phosphor particles constituting a scintillator layer and resolution characteristics thereof.
FIG. 7 is a diagram showing an example of a relationship between the number of phosphor particles constituting the scintillator layer in the thickness direction and the transmittance of fluorescence transmitted through the scintillator layer.
FIG. 8 is a diagram for explaining a structure of a partition formed in parallel with a traveling direction of emitted X-rays.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray detector, 11 ... Photoelectric conversion board, 12 ... Pixel, 13 ... Photodiode, 14 ... Thin film transistor (TFT), 15 ... Storage capacitor, 38 ... Partition part (groove or partition part), 39 ... Scintillator layer, 391: first scintillator layer, 392: second scintillator layer, 41: fluorescence

Claims (8)

A photoelectric conversion substrate in which a plurality of pixel-based photoelectric conversion elements are arranged,
A scintillator layer disposed on the photoelectric conversion substrate,
A partition portion formed on the photoelectric conversion substrate and partitioning the scintillator layer in pixel units;
With
The scintillator layer includes a first scintillator layer on the photoelectric conversion substrate, and a second scintillator layer on the first scintillator layer,
A radiation detector, wherein the first scintillator layer is disposed between the photoelectric conversion substrate and the partition. A photoelectric conversion substrate in which a plurality of pixel-based photoelectric conversion elements are arranged,
A scintillator layer disposed on the photoelectric conversion substrate,
A partition portion formed on the photoelectric conversion substrate and partitioning the scintillator layer in pixel units;
With
The scintillator layer includes a first scintillator layer disposed on the photoelectric conversion substrate and formed of phosphor particles having a first average particle diameter D1; and a first scintillator layer disposed on the first scintillator layer. A second scintillator layer composed of phosphor particles having a larger second average particle diameter D2.
A radiation detector, wherein at least the first scintillator layer is arranged between the photoelectric conversion substrate and the partition. The radiation detector according to any one of claims 1 to 3, wherein the first scintillator layer is formed of phosphor particles having an average particle diameter substantially equal to that of the second scintillator layer. . The relationship between the average thickness T1 of the first scintillator layer and the average particle diameter D1 of the phosphor particles constituting the first scintillator layer is T1 ≧ D1. Item 4. The radiation detector according to any one of items 3. 5. The radiation detection device according to claim 1, wherein an average thickness T1 of the first scintillator layer is equal to or less than a distance T2 between the photoelectric conversion substrate and the partition. vessel. The first average particle diameter of the phosphor particles constituting the first scintillator layer was D1, the average film thickness of the first scintillator layer was T1, and the average filling rate of the phosphor particles in the first scintillator layer was F1. When
D1 ≧ T1 · F1 / 10
The radiation detector according to any one of claims 1 to 5, wherein The radiation detector according to claim 1, wherein the partition is a partition. The radiation detector according to claim 1, wherein the partition is a groove.

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