JPH0695048B2 - Infrared detector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an infrared detector for an earth sensor used for attitude control of a satellite in the space industry.

2. Description of the Related Art As an infrared detector for an earth sensor, one using a thermistor, a thermopile or a pyroelectric element is known.
Among them, those using a thermistor detect the infrared condensing lens in order to improve the infrared detection sensitivity as shown in Research Report No. 177, pp. 65-66 of the Electrotechnical Laboratory. A device integrated with an element has been put into practical use.

3 (a) and 3 (b) are examples in which a pyroelectric element is integrated with a lens. In the figure, 11 is an infrared detection element using a pyroelectric element, 12 is a condenser lens formed of Ge or the like that transmits infrared rays, and 13 is a back surface as a signal extraction electrode formed on the back surface of the pyroelectric element 11. Electrodes, 16 are infrared receiving electrodes, which are used as ground electrodes. 14 and 15 are a signal extraction lead and a ground lead, respectively.

In such a configuration, the infrared light that has entered the condenser lens 12 is condensed by the condenser lens and enters the infrared detection element 12, and a signal is extracted from the signal extraction electrode 13 by the pyroelectric effect.

The effects of integrating the infrared detection element 11 and the condenser lens 12 are as follows. That is, as shown in FIG. 3, an infrared detection element
By bringing 11 into close contact with the condenser lens 12, the optical system can be brightened while the performance deterioration due to optical aberration is suppressed to a negligible level. Therefore, the efficiency of collecting infrared rays is improved, and the infrared detection sensitivity can be improved.

However, since the infrared detection element 11 is in close contact with the condenser lens 12, the thermal time constant, which is one of the important characteristic items of the infrared detector, becomes short. In the case of a pyroelectric element, the thermal time constant is several tens of mS when it is not integrated with a condenser lens, but it is on the order of 0.1 mS when it is closely attached to the lens.

On the other hand, from the standpoint of earth sensor design, in order to efficiently detect the infrared input signal when detecting the earth's edge, frequency characteristics corresponding to the main frequency band 60 to 300 Hz of the input signal are required.
In the pyroelectric element, if the thermal time constant is shortened, the sensitivity decreases in proportion to it.
It is necessary to set the thermal time constant equal to or higher than 0 Hz.

Considering the design margin, GT2mS will be a requirement on the earth sensor side.

As described above, in order to increase the light collection efficiency, the thermal time constant of the infrared detector integrated with the lens becomes shorter than the value required for the earth sensor design. Then, there is a problem that the sensitivity is lowered, and the reduction rate has a far greater effect than the increase of the input signal obtained by the improvement of the light collection efficiency, and the sensitivity is lowered rather than the overall improvement. is there.

The present invention solves such problems, and an object thereof is to obtain an infrared detector having a large thermal time constant by integrating an infrared detection element and a condenser lens.

Means for Solving the Problems In order to solve the above problems, the present invention provides a space between the condensing lens and the infrared detection element on the effective light receiving surface thereof, which is 1/4 or less of the wavelength of infrared rays to be detected. , The thermal time constants try to satisfy the earth sensor design requirements.

Action In the above configuration, since there is a space between the infrared detection element and the condenser lens, thermal diffusion from the infrared detection element to the condenser lens becomes small, and the thermal time constant becomes large. Further, since this distance is λ / 4 or less, the optical aberration can be almost ignored.

Example In the earth sensor, the emission band of carbon dioxide gas is 14 to 16
Infrared rays in the μm band or 17 to 35 μm band, which is the radiation band of water vapor, are the targets of observation. When detecting such long-wavelength infrared rays, the thermal time constant of the earth sensor is set by providing a space between the condenser lens and the infrared detecting element while maintaining the condition that optical aberration does not adversely affect the performance of the earth sensor. It is possible to increase to the design required value. According to the optical design, the distance may be λ / 4 or less. Here, λ is the shortest wavelength of infrared rays to be detected. Therefore, if λ = 14 μm,
The distance between the condenser lens and the infrared detection element can be increased to 3.5 μm.

The thermal time constant ^τ T is given by the following equation.

Here, H is the heat capacity of the infrared sensing element effective heat-sensitive part (J /
℃), G is the heat dissipation capacity (J / ℃ ・ S) from the effective heat-sensitive part of the infrared detection element to the heat sink (the condenser lens acts as a heat sink).

The heat dissipation capability G includes three types of factors of heat radiation, convection, and heat conduction, but since heat conduction is the main factor, if this is suppressed, G will decrease and the thermal time constant ^τ T will increase.

If there is a space of several μm between the condenser lens and the infrared detection element,
The heat dissipation during that time is largely due to the convection due to the gas and the heat radiation. Also, if the atmospheric pressure in this interval is reduced, convection is also reduced. The remaining factor is heat that escapes by conduction from the periphery of the infrared detection element to the lens, which is the heat sink body, via the support base. This depends on the structure of the infrared detection element and the method of fixing it to the lens, but it is a factor that can be controlled by design and can be positively used for designing the infrared detector.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the structure of a lens-integrated pyroelectric infrared detection element 22 in one embodiment of the present invention.

The infrared condensing lens 12 is made of germanium, is a single-convex lens with a diameter of 3 mmφ, and has a convex surface with a radius of curvature of 2.5 mm and a thickness of 2 mm. A zinc sulfide film is vapor-deposited, which serves as an antireflection film for infrared rays in the 14 to 16 μm band.

The optical design conditions of the above infrared condensing lens are determined in combination with the main lens (objective lens) to be combined therewith and are not related to the essence of the present invention.

The pyroelectric element 11 is a lead titanate ceramic having a size of 1 mm × 1 mm × 10 μm, and an effective light receiving surface, that is, a sensitive portion has a central portion of 0.3 mmφ of 1 mm × 1 mm. A nichrome electrode as a ground electrode 16 is vapor-deposited on this portion on the infrared incident surface, that is, the surface facing the condenser lens 12 so that the sheet resistance is 1 cm wide and 300 cm to 400 Ω at 1 cm intervals. This nichrome electrode film 16 is 0.2 mm wide and is vapor-deposited by extending it to the edge of a 1 mm × 1 mm pyroelectric element for taking out the lead in one direction. Similarly, on the back surface, an aluminum vapor deposition film is vapor-deposited with a thickness of 1 to 2 μm as the signal extraction electrode 13.

On the other hand, the thickness of the element support frame 17 is 2 on the flat surface of the condenser lens 12.
An aluminum film of μm is vapor-deposited. Evaporation portion, except for the condenser lens center 0.6 mm ^□, of about 1 mm × 1 mm, as further shown in FIG. 1 (b) to derive the infrared light-receiving surface electrode 16
Add 0.3mm of lead mounting part. It should be noted that the space between the condenser lens 12 and the pyroelectric element 11 should not be sealed.
At least two or more locations are provided on the aluminum vapor deposition element support frame 17 without vapor deposition.

The pyroelectric element 11 is bonded onto the element supporting frame 17 with an adhesive. The infrared incident surface electrode extraction side (the left side of the pyroelectric element 11 in FIG. 1) was bonded with a conductive adhesive to establish electrical continuity and used as a ground electrode. On the other hand, the right side of the pyroelectric element 11 in FIG. 1 is bonded with an insulating adhesive. After that, a fine gold wire (in 30μ) is connected to each lead mounting portion with an ultrasonic bonder, and the signal extraction lead 14 and the ground lead 16 are attached.

With the above, a pyroelectric infrared detection element with a condenser lens was produced.
Using this, an infrared detector for earth sensor having a structure as shown in FIG. 2 was produced. FIG. 2 shows an example of a two-element infrared detector, in which an infrared interference filter which transmits only infrared rays of 14 to 16 μm or 17 to 35 μm is used for the window plate 18. Infrared detector 22 with a condenser lens on the mount base 20
Are assembled and vacuum-sealed with a cap 19. Regarding the signal and the power source, the signal is taken out or the power source is applied using the pin terminal 21. The pin terminal 21 has four pins including a ground pin and a case pin.

The thermal time constant of this infrared detector is 3mS, which satisfies the design requirements of the earth sensor.

In the second embodiment, the element supporting frame 17 is made of zinc sulfide which is a material for the antireflection film of the lens instead of the aluminum vapor deposition film.
Although the thickness was 2 μm and the dimensions were the same, a 0.2 mm wide aluminum vapor-deposited film was vapor-deposited on the zinc sulfide frame on the side from which the infrared incident surface electrode was taken out, and the earth lead was taken therefrom. In this example, dry nitrogen gas sealing was performed without vacuum sealing.

The thermal time constant was 2 mS, which satisfied the required value of the earth sensor.

As described above, according to the present invention, the pyroelectric infrared detection element is fixed to the infrared condensing lens with an interval of 1/4 or less of the wavelength of infrared rays detected, and the infrared detection element An infrared detector for earth sensors housed in a container with a transparent window, with a thermal time constant of 2 mS
As described above, it was possible to maintain the sensitivity improvement due to the improvement of the light collection efficiency and achieve the voltage sensitivity improvement of about 2.5 times as compared with the element not integrated with the light collection lens. It should be noted that in the present embodiment, the noise increased slightly more than 1.6 times, but the improvement in sensitivity exceeded it, and the S / N was improved by 1.5 times. Noise can be reduced by reducing the element thickness. For example, reducing the element thickness to 1/3 reduces the noise. The S / N ratio can be improved 2.5 times.

[Brief description of drawings]

1 (a) and 1 (b) are a side view and a plan view of an embodiment of a pyroelectric infrared detection element integrated with a lens, which is a main part of an infrared detector according to the present invention, and FIG. 2 is a view according to the present invention. FIG. 3A and FIG. 3B are a side view and a plan view of a conventional lens-integrated pyroelectric infrared detection element, respectively, showing a sectional side view showing a configuration in an embodiment of an infrared detector for an earth sensor. 11 ... Pyroelectric element, 12 ... Condensing lens, 13 ... Signal extraction electrode, 14 ... Signal extraction lead, 15 ... Ground lead,
16 …… Ground electrode, 17 …… Element support frame, 18 …… Window plate, 19
...... Cap, 20 ...... Mount base

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kunio Nakamura Inventor Kunio Nakamura 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Matsushita Giken Co., Ltd. (72) Inventor Eizo Yamaka 2-chome Fujigaoka, Midori-ku, Yokohama Address 2

Claims (3)

[Claims] 1. A pyroelectric infrared detecting element is fixed at an interval of 1/4 or less of the shortest wavelength of infrared rays detected by an infrared condenser lens and is housed in a container equipped with an infrared filter window. An infrared detector characterized in that 2. The infrared detector according to claim 1, wherein the inside of the container is sealed under reduced pressure. 3. An infrared filter window having a band of 14 to 16 μm or 17 to 35
The infrared detector according to claim 1, comprising an infrared interference filter that selectively transmits infrared light in the μm band.