JPH0726867B2 - Multi-element photo detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-element photodetector, and particularly to a suitable detector structure having a wide light receiving area and comprising a semiconductor photoelectric conversion element array divided into multi-elements. Regarding

[Background of the Invention]

In the semiconductor photoelectric conversion device, the semiconductor chip of the photosensitive portion is installed on a ceramic or resin stem or substrate,
It is used as a photodetector by being fixed to the measuring device and making an electrical connection. The photoelectric conversion element is also applied as a radiation detector for measuring a one-dimensional or two-dimensional (plane) radiation intensity distribution by installing a scintillator for converting radiation on the light incident surface. There is.
The application as a radiation detector is a multi-element X-ray detector for an X-ray CT apparatus. With this CT device, 2000 on the circumference
An array of detectors made up of each element or more, or a detector in which 500 elements are arranged in an arc shape is used to accurately measure the X-ray intensity distribution, and the data is used for image processing by a computer. , To make a cross-sectional image of the subject. The accuracy of measurement data is the main factor that determines the superiority of the image,
Reduction of sensitivity variation between detector elements and signal / noise ratio (S /
N) improvement is required. As shown in FIG. 2, the conventional X-ray detector has a structure in which a semiconductor photoelectric conversion element 1 is fixed on a surface of a substrate 2 with an epoxy adhesive 6 and an output signal is taken out from a connector 5. It should be noted that the scintillator installed in close contact with the upper surface of the conversion element 1 in the figure is omitted from the figure because it is not directly related to the present invention. The semiconductor photoelectric conversion element 1 is a photodiode or a phototransistor, and semiconductors such as Ge, Si, InP, GaAs, CdTe, AlSb, and CdS are used. Applications related to the invention, eg X
A PIN structure of Si is suitable for the element used in the line detector. In the case of this X-ray detector, since it is necessary to have a multi-element structure, the silicon photodiode 1 is fixed to the surface of the substrate 2 as shown in FIG. A plurality of silicon photodiodes each having a width of about 1 mm and a length of about 30 mm are arranged in parallel to form a block unit. If necessary, a plurality of these blocks may be arranged to form a detector having more elements. FIG. 6 shows another example of the detector, in which a plurality of photoelectric conversion elements each having a width of about 1 mm and a length of 2 to 3 mm are arranged on the substrate 2, and signals are independently extracted from each element to obtain a one-dimensional intensity distribution. To measure. In the case of 20 elements having the structure shown in FIG. 5, the size of the semiconductor photoelectric conversion element is width 20 ^mm (width 1 mm × 20 elements) × length 30 ^mm . The structure shown in FIG. 6 has 20 to 30 conversion elements, and the size is 2-3 ^{mm in} length × 30 ^{mm in} width (1 ^{mm in} width × 1 ^{mm in} width).
30 elements) and all have a large area. When a semiconductor conversion element occupying such a large area is fixed on a substrate, a problem that does not occur in a semiconductor conversion element of about 1 ^mm x 1 ^mm occurs. That is, the first is that the semiconductor photoelectric conversion element is stressed due to the difference in the coefficient of thermal expansion, and the second is that when the substrate is attached to the detector structure or the like using the attachment holes 3, the substrate is deformed and the semiconductor photoelectric conversion element is deformed. This means that stress is applied to the conversion element.

Actually calculating the first example (Fig. 5), the coefficient of thermal expansion of the silicon element is 2.3 × 10 ^-6 , the coefficient of thermal expansion of the glass fiber reinforced epoxy resin is 20 × 10 ^-6 , If there is a temperature change of 10 ° C in a semiconductor photoelectric conversion device with a length of 30 mm, 6 × 10
A strain of ^-3 occurs, which causes stress.

In the case of the second example (FIG. 6), when the amount of strain is measured by actually performing the mounting work, a strain of 3 × 10 ⁻³ is generated and stress is applied.

When stress is applied to the semiconductor photoelectric conversion element, the resistance value changes due to the piezoresistance effect. Therefore, in the photoelectric conversion element (silicon photodiode, etc.), the dark current changes. Therefore, in the case of highly accurate measurement, it is necessary to always take measures to compensate the dark current. Especially, a change due to mechanical strain causes a measurement error in the form of vibration noise, which causes a significant deterioration in accuracy.

[Object of the Invention]

The object of the present invention is to prevent the change in the electrical characteristics due to the piezo effect that occurs when stress is applied to the semiconductor photoelectric conversion element, so that stress is applied to the semiconductor photoelectric conversion element even in the state where a factor of thermal or mechanical fluctuation occurs. It is an object of the present invention to provide a multi-element photodetector having a structure in which is not added.

[Summary of the Invention] The semiconductor photoelectric conversion element has a structure in which it is fixed on a substrate made of a ceramic or resin electrical insulator in order to extract an electric signal and connect it to a circuit due to the configuration of the photodetector. .
Particularly in the case of multiple elements, it is necessary to attach a connector, and a substrate having a strength that does not easily deform mechanically is used. In this case, the semiconductor photoelectric conversion element and the substrate for fixing the semiconductor photoelectric conversion element are not fixed in close contact with each other but fixed with a flexible material interposed therebetween. As a result, the influence of the difference in thermal expansion on the element and the influence of the deformation of the substrate are blocked, and the output of the photodetector is stably obtained.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. The silicon photoelectric conversion element plate 1 divided into a plurality of elements is fixed to one surface of the printed board 2, and the output of each element is connected to the wiring of the printed board 2 to obtain a one-dimensional light intensity distribution for extracting a signal from the socket 5. It is an example of a multi-element photodetector for the purpose of measurement.

The printed circuit board 2 is made of various ceramic plates or glass fiber reinforced resin, such as epoxy, polyimide, or bakelite. The signal output of each element of the photoelectric conversion element 1 is connected to the pad portion of the printed board 2 by bonding and is connected to the socket 5 through the wiring pattern of the multilayer board. The thickness of the substrate needs to be 1 to 2 ^mm for the ceramic plate and 3 to 4 ^{mm for the} resin plate in order to maintain the strength.

The photoelectric conversion element 1 uses a Si PIN type photodiode. When the light receiving area becomes large, the PIN type is suitable for reducing the junction capacitance. The dimensions of one element are 1 mm in width and 30 mm in length, and these elements are formed by 16 to 20 elements in one Si chip, and each element is electrically connected so that it is not affected by adjacent elements. And optically separated. The influence from adjacent elements, that is, the amount of crosstalk is suppressed to about 1%. The width of the Si chip is 20
The size of the device is 20 mm, and these are precisely aligned and fixed on the substrate. The width of the substrate is the same as the width of the Si chip, or
About 0.05 mm larger than the Si chip width. This is because when a plurality of substrates are arranged to form a detector having a larger light receiving surface, a gap between the substrates is eliminated, and an end portion of the Si chip is prevented from being contacted and damaged. The silicon chip 1 is fixed to the printed circuit board 2 with a joining member 4. At this time, if the ordinary epoxy adhesive is used for strong bonding, when vibration or stress is applied to the printed board portion, the stress is transmitted to the silicon chip detection portion and becomes a noise signal.

In order to prevent this problem, the present invention uses the joining member 4 having flexibility in a state after being bonded, and the deformation stress and vibration are absorbed by the joining member. When the silicon chip and the printed circuit board are directly bonded to each other, a rubber-based adhesive is used. As typical examples, rubber latex adhesive such as butyl rubber, nitrile rubber and natural rubber is preferable. Further, the thickness of the adhesive may be 20 to 50 μm, and if it is thinner than this, the absorbing effect becomes small. Furthermore, if a rubber-based sheet having a thickness of 50 μm is inserted between the silicon chip and the printed circuit board and fixed with a rubber-based adhesive, the effect is still greater. In order to confirm the effect of the embodiment, as shown in FIGS. 3 and 4, strain gauges 10 and 11 are pasted on the printed circuit board surface and the silicon chip surface, and the printed circuit board 2 is bent and deformed in its longitudinal direction. The strain was applied and the amount of strain was measured. FIG. 3 shows a case where the silicon chip 1 is directly fixed to the printed circuit board 2 with the epoxy adhesive 6, and the strain gauge 10 on the printed circuit board surface is
^{When a} strain of ^{-4 in} the compressive direction is applied, strain of the same magnitude in the tensile direction is generated in the strain gauge 11 on the silicon chip, and the silicon chip is completely following and deformed.

Fig. 4 shows 50 between the printed circuit board 2 and the silicon chip 1.
When a bending deformation is applied in the longitudinal direction of the printed circuit board 2 in the same manner when the rubber sheet 4 having a thickness of μm is inserted and fixed, the strain gauge 11 on the silicon chip is the strain gauge of the printed circuit board 2.
It was about 1/2 of the strain amount of 10. That is, the rubber sheet absorbs the deformation and reduces the deformation of the silicon chip. Therefore, the conduction of vibration to the silicon chip is also reduced.

〔The invention's effect〕

According to the present invention, the stress applied to the silicon element can be reduced due to the strain caused by the difference in the thermal expansion coefficient between the silicon element and the substrate. That is, in the case of a combination of a silicon element and a glass fiber reinforced epoxy resin substrate, the amount of change in resistance caused by the piezoresistive effect is
It can be less than 1/2. Especially when aligning a plurality of substrates and measuring a one-dimensional intensity distribution over a long distance, variations in characteristics between individual substrates are reduced,
The operation of the correction process for making the sensitivity constant and the calculation process are simplified, and accurate measurement is possible.

[Brief description of drawings]

FIG. 1 is an external view of a multi-element photodetector of an embodiment of the present invention, FIG. 2 is a side view of a conventional photodetector, and FIGS. 3 and 4 are light for explaining the effect of the present invention. Side view of the detector, Fig. 5,
FIG. 6 is a plan view of an example of a multi-element photodetector. 1 ... Photoelectric conversion element, 2 ... Printed circuit board, 3 ... Mounting hole, 4
... Joining member, 5 ... Socket, 6 ... Adhesive.

Claims (1)

[Claims] 1. A multi-element photodetector comprising a semiconductor photoelectric conversion element and a printed circuit board for fixing the semiconductor photoelectric conversion element, wherein the semiconductor photoelectric conversion element and the printed circuit board are fixed by a flexible joining member. Multi-element photodetector.