JP3071817B2 - Semiconductor radiation detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a semiconductor radiation detector, and more particularly to a semiconductor radiation detector used for a medical or industrial camera, a tomography apparatus, or the like that requires an array arrangement structure. .

[Prior art] A semiconductor radiation detector using CdTe, which is a compound semiconductor, has characteristics that it has a large absorption coefficient of X-rays and γ-rays, can be used at room temperature, and can be miniaturized into an array. Therefore, it has begun to be applied to monitors around reactors, small survey meters, medical tomography devices, and the like.

If the semiconductor radiation detector has one detection element,
The detection element is fixed in the air by a wire for extracting a signal from the detection element, or the detection element is fixed by a material such as an epoxy adhesive that has little radiation attenuation. However, in a semiconductor radiation detector in which a plurality of detection elements are arranged in an array, since spatial position accuracy of each detection element is required, it has been proposed to fix each detection element to a support portion such as a substrate. ing. Further, when positional accuracy is required even with one detecting element, it is necessary to fix the detecting element to the supporting portion.

[Problems to be Solved by the Invention] However, conventionally, no consideration has been given to the fixing method when the detection element is fixed to a support portion such as a substrate or the effect of the material of the support portion on the detection characteristics. Was not secured.

An object of the present invention is to provide a semiconductor radiation detector capable of securing sufficient reliability with little influence on radiation detection characteristics even when an element portion is fixed to a support portion.

Means for Solving the Problems The object is to provide an element portion made of a radiation-sensitive compound semiconductor, a pair of electrode portions formed on opposite surfaces of the element portion, and one of the pair of electrode portions. Formed on the side of
An adhesive layer having a thickness of about 500 μm or more, and a support section for fixing the element section via the adhesive layer and the one of the pair of electrode sections, and a difference in thermal expansion coefficient between the element section and the support section. (Δα) is about 5.1 × 10 ⁻⁶ / ° C. or less, and the element part is Cd
This is achieved by a semiconductor radiation detector characterized by consisting of Te.

According to the present invention, the thickness of the adhesive layer is as thick as about 500 μm or more, and the difference (Δα) in the coefficient of thermal expansion between the element part and the support part is about 5.1 × 1.
Since it is as small as 0 ⁻⁶ / ° C. or less, the support portion has little influence on the radiation detection characteristics of the element portion, and sufficient reliability can be secured.

Example A semiconductor radiation detector according to a first example of the present invention will be described with reference to FIGS.

Approximately 1.2 mm thick CdTe crystal 1 as an element for detecting radiation
0 is formed in about 2mm square. On both surfaces of the CdTe crystal 10, Pt electrodes 12 and 14 having a thickness of about 100 nm are formed. One Pt electrode 14 of the CdTe crystal 10 is bonded and fixed to a substrate 18 by an Ag epoxy layer 16 which is a conductive adhesive having a thickness of about 20 μm. The curing of the Ag epoxy layer 16 was performed at about 60 ° C. for about 4 hours.

In this embodiment, since the Ag epoxy layer 16 is as thin as about 20 μm,
The CdTe crystal 10 as an element part is supported by the substrate 18 as a support part. Therefore, in the present embodiment, it is necessary that the coefficient of thermal expansion of the substrate 18 as the support part does not differ from the coefficient of thermal expansion of the CdTe crystal 10 as the element part by a certain degree or more. However, since it depends on how much the substrate 18 can absorb the distortion due to the difference in the coefficient of thermal expansion, the elastic coefficient E of the substrate 18
(Kg / mm ² ) is also a determining factor.

If the coefficient of thermal expansion of the substrate 18 is significantly different from the coefficient of thermal expansion of the CdTe crystal 10, the radiation characteristics of the semiconductor radiation detector deteriorate due to heating. This deterioration appears as a decrease in the peak position in the energy spectrum and a deterioration in the energy resolution. This means that when heated, the substrate 18 and CdTe
Stress is applied to the interface between the CdTe crystal 10 and the Pt electrode 14 due to the difference in the coefficient of thermal expansion of the crystal 10, and this portion is altered. This altered part has a disordered crystal structure and becomes a high-resistance layer, and CdTe
This is because, of the voltages applied to the crystal 10, the voltage that effectively works for carrier collection is reduced, and this is a main factor of characteristic deterioration. Note that the resolution did not recover even if the radiation detector whose energy resolution had once deteriorated was removed from the substrate 18.

As a substrate 18 to determine available substrate materials
Measures the characteristics degradation when using CdTe substrate, glass substrate made of borosilicate glass, dense alumina substrate containing 92% alumina, Teflon (duPont trademark, substance name: polytetrafluoroethylene) substrate, glass epoxy substrate did. Radiation is obtained from ²⁴¹ Am (Americium) 6
Using a 0 keV γ-ray, a bias voltage of 60 V was applied to the Pt electrode 12 and the Pt electrode 14, and the energy spectrum was measured.
A change in the half width ΔE of the V peak was detected. A load was applied to the semiconductor radiation detector by repeating a cycle of heating at 125 ° C. for 1 hour and then naturally cooling for 1 hour. Measurements were taken until the total heating time was 24 hours.

FIG. 2 shows the measurement results. The horizontal axis indicates the total heating time (hr) at 125 ° C., and the vertical axis indicates the half width ΔE (keV) of the 60 keV peak of the energy spectrum.

As shown in FIG. 2, in the case of the CdTe substrate, the glass substrate, and the alumina substrate, the half width Δ
E did not change from 5 keV.

In the case of the Teflon substrate, the half width ΔE gradually increases as the total heating time increases, and the total heating time is 20 ke for 24 hours.
It became V.

In the glass epoxy substrate, the half width ΔE sharply increased as the total heating time increased, and reached 30 keV in 3 hours. In the glass epoxy substrate, the half-width ΔE was already deteriorated after the heat treatment at 60 ° C. for 4 hours in order to cure the Ag epoxy adhesive, and the carrier was so large that the half-width ΔE could not be defined in the 125 ° C. heating test. Collection characteristics deteriorated.

From the above measurement results, it was found that the substrate 18 of the supporting portion is most preferably a CdTe substrate, a glass substrate, and an alumina substrate, and the Teflon substrate is also within the allowable range, but the glass epoxy substrate causes unacceptable characteristic deterioration. .

The following table shows the product (Δα × E) of the difference Δα between the coefficient of linear expansion of the substrate material and the coefficient of linear expansion of the CdTe crystal in each substrate, and the elastic coefficient E. From this table, the difference in linear expansion Δα is 10 × 10 ⁻⁶ /
It was found that when the temperature was lower than or equal to ° C., the characteristic deterioration of the semiconductor radiation detector was within an allowable range. Δα is 2 × 10
^It can be seen that it is more preferable that the temperature is ⁻⁶ / ° C. or less.

A semiconductor radiation detector according to a second embodiment of the present invention will be described with reference to FIGS.

In this embodiment, the Ag epoxy layer 16 is formed as thick as 500 μm, and the distortion due to the difference in the coefficient of thermal expansion of the substrate 18 is reduced.
So that it is absorbed. Therefore, in this embodiment, the Ag epoxy layer 16 instead of the substrate 18 functions as a support for supporting the CdTe crystal 10.

FIG. 4 shows the characteristic deterioration when the Ag epoxy layer 16 is 500 μm thick using a Teflon substrate as the substrate 18.
Is shown in comparison with the case where the thickness is 20 μm.

When the Ag epoxy layer 16 has a thickness of 20 μm, the half width ΔE gradually increases as the total heating time increases, and the total heating time reaches 20 keV in 24 hours.
When the thickness is m, the half width ΔE increases only slightly even when the total heating time increases, and the total heating time is about 10 keV even when the total heating time is 24 hours, indicating that the characteristic deterioration is within an allowable range.
From the table, the difference Δα of the linear expansion coefficient in Ag epoxy is 10 × 10
^Although it is ^-6 / ° C or higher, it is considered that the elastic modulus is small and the stress at the electrode interface is reduced.

In this case, the elastic modulus of the Ag epoxy layer serving as a supporting portion (E) is ^{10 -3 ~10 -1 [kg / mm} 2], 1 if [kg / mm ^2] Hereinafter, characteristic degradation is allowable range It turned out to be.

The present invention is not limited to the above embodiment, and various modifications are possible.

For example, the substrate is not limited to the above-described substrate, and may be any material as long as the substrate satisfies the above selection criteria.

In addition, other conductive epoxy, non-conductive epoxy, alloy metal such as solder may be used instead of Ag epoxy, and if these satisfy the above-mentioned conditions, they are formed thickly and used as a support. May function.

[Effects of the Invention] As described above, according to the present invention, even if the element section is fixed to the support section, the influence on the radiation detection characteristics is small, and sufficient reliability can be ensured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a semiconductor radiation detector according to a first embodiment of the present invention, FIG. 2 is a graph showing measurement results of a heating load test of the semiconductor radiation detector according to the first embodiment of the present invention, FIG. 3 is a sectional view of a semiconductor radiation detector according to a second embodiment of the present invention, and FIG. 4 is a graph showing measurement results of a heating load test of the semiconductor radiation detector according to the second embodiment of the present invention. In, 10 ... CdTe crystal 12, 14 ... Pt electrode 16 ... Ag epoxy layer 18 ... Substrate

Claims (1)

(57) [Claims] An element portion made of a compound semiconductor which is sensitive to radiation; a pair of electrode portions formed on opposite surfaces of the element portion; and a thickness formed on one side of the pair of electrode portions. About 500
a bonding layer having a thickness of at least μm, and a supporting portion for fixing the element portion via the adhesive layer and the one of the pair of electrode portions. But about 5.
A semiconductor radiation detector having a temperature of 1 × 10 ⁻⁶ / ° C. or less, wherein the element portion is made of CdTe.