Thermal infrared detector

Details Thermal infrared detector Thermal infrared detector

1996-07-18

1998-04-21

Glick, Edward J.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

2503383, G01J 502, H01L 2314

Patent

active

057420521

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a thermal infrared detector that is used in devices such as a radiation thermometer which measures temperature without contact, or in trespass alarms that use infrared rays radiated from a human body to warn of human presence.


DESCRIPTION OF THE PRIOR ART

Generally, infrared detectors are classified into two types, quantum and thermal. Quantum infrared detectors use the fact that a electric charge is generated directly by infrared irradiation due to the photo-electromotive effect and photo-conductive effect of the infrared detection element, and thermal infrared detectors use the change in polarization (pyroelectric-type detector), the change in resistance (bolometer) or generation of electromotive force (thermopile) that is caused by the change in temperature of the infrared detection element that rises as infrared rays are absorbed. Moreover, thermal infrared detectors must effectively convert incident infrared rays into heat, and a large temperature change of the element is necessary.
FIG. 8 shows the change of heat that is brought about by the infrared rays that are incident on the infrared detection element comprising an infrared detector element 1, a circuit board 4 and a support 20 between the infrared detector element 1 and the circuit board 4.
A part of the infrared rays that are incident on the infrared detector element 1 are reflected by the surface. The remaining part is either absorbed by the element 1 or passes through the element and exits to the outside. Of these infrared rays, those that can be effectively converted to heat and that contribute to the large change of temperature of the element 1 are the infrared rays that are absorbed by the element 1.
Moreover, the thermal energy of the infrared rays that are absorbed by the aforementioned infrared detector element 1 not only cause the temperature of the element 1 to rise, but are also radiated from the surface of the element 1 and are consumed by convection or by being transferred to the support 20 that holds the element 1.
Therefore, in order to obtain a high-precision thermal type infrared detector, it is necessary to increase the absorption efficiency of infrared rays, and it is necessary to reduce the heat that is lost from the infrared detector due to radiation, convection or heat transfer to the element support. Normally the largest of these three kinds of heat loss is the heat that is lost due to heat transfer to the support of the infrared detector element. In the prior art, there have been four systems known for preventing the heat lost due to this kind of heat transfer.
(1) FIG. 9 shows the first system. Here, metal wires, which are also used as the lead wires for fetching the generated electric signal, are used as the support 21 for the infrared detector element 1. In this method, the amount of heat lost due to the aforementioned heat transfer is the smallest, however it is very weak under impact and it is difficult to produce.
(2) FIG. 10 shows a second system. Here, in place of the metal wires used in the first method, metal pins are used as the support 22 for the infrared detector element 1. In this method, inner pins (0.5 mm dia.) of a detector package such as the TO-5 are commonly used metal pins; however, the heat capacity of this pins is large so the heat loss becomes large, and the reduction in sensitivity of the detector cannot be ignored. Therefore, when this method is actually used it is necessary to use an infrared detector element whose surface area is larger than that of the photo-receptor electrode, and the portion of the photo-receptor electrode whose temperature rises due to the infrared rays must be kept separated from the metal pins which fetch the electric signal. Therefore, the material cost of the infrared detector element 1 is very high, and there is a high possibility of the element 1 being damaged.
(3) FIG. 11 shows a third system. Here, an insulating material such as ceramic, glass or resin that is formed in a rectangular block shape is used as the s

REFERENCES:
patent: 4009516 (1977-03-01), Chiang et al.
patent: 4250075 (1981-02-01), Monroe et al.
patent: 4354109 (1982-10-01), Gelpey et al.
patent: 4740700 (1988-04-01), Shaham et al.
patent: 4815199 (1989-03-01), Jenner et al.

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