Batteries: thermoelectric and photoelectric – Thermoelectric – Thermopile
Reexamination Certificate
2001-12-07
2004-03-09
Kalafut, Stephen (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Thermopile
C257S467000
Reexamination Certificate
active
06703554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared detecting device.
2. Description of the Prior Art
In general, an infrared detecting device includes the thermopile type, pyroelectric type, and bolometer type. The thermopile infrared detecting device includes the types shown in
FIGS. 5 and 6
, for example.
The difference between the thermopile infrared detecting devices shown in
FIGS. 5 and 6
depends on the anisotropic etching method of the micromachining technique.
In the case of the infrared detecting device in
FIG. 5
, etching is started from the surface of a semiconductor substrate to form a diaphragm having a low thermal conductivity on the surface side and form a thermopile on the diaphragm.
In the case of the infrared detecting device in
FIG. 6
, the thermopile is formed on the surface of a semiconductor substrate, however etching is started from the back side of the semiconductor substrate.
The infrared detecting device in
FIG. 5
is described below. As shown in
FIG. 5
, the thermopile infrared detecting device S
1
is provided with a semiconductor substrate
101
, a diaphragm
102
set on the semiconductor substrate
101
and having a low thermal conductivity, a thermopile
104
formed on the diaphragm
102
, and a heat absorption film
105
formed through an insulation layer
103
located at the central portion. Thermopile
104
is formed by arranging a plurality of thermocouples
113
constituted by arranging p-type polysilicon
110
and n-type polysilicon
111
, having the same width and thickness relative to each other, in parallel and electrically connecting them in series via aluminum wiring
112
.
In order to improve the performance of the above infrared detecting device, it is required to increase the ratio of an output signal to a noise, that is, so-called SN ratio (Signal to Noise ratio). However, in the case of the above conventional infrared detecting device S
1
, the difference between electrical resistivities of the p-type polysilicon
110
and n-type polysilicon
111
of the thermocouple
113
and the difference between thermal conductivities of them are not considered at the time of designing the thermopile
104
and the width and thickness of each polysilicon are the same. Therefore, there is a problem in that it is difficult to obtain the device with high SN ratio and it is the subject to solve the above-mentioned problem.
SUMMARY OF THE INVENTION
The present invention is made in view of the aforementioned subject and it is an object to provide an infrared detecting device capable of setting sectional areas of p-type polysilicon and n-type polysilicon of a thermocouple to values suitable for improving the SN ratio.
The infrared detecting device according to the present invention is characterized by comprising a semiconductor substrate, a diaphragm set on the semiconductor substrate and having low thermal conductivity, a thermopile formed on the diaphragm by arranging a plurality of thermocouples composed of p-type polysilicon and n-type polysilicon in a row and electrically connecting the thermocouples with each other in series, and a heat absorption film formed on a detecting section of the thermopile through an insulation layer, wherein the p-type and n-type polysilicons are different in their sectional areas from each other at a position between a hot junction and a cold junction of each of the thermocouples forming the thermopile, in order to achieve the above subject on the prior art.
The infrared detecting device according to the first preferred embodiment of the present invention is constituted so that the p-type and n-type polysilicons are different in their average sectional areas from each other at the position between the hot and cold junctions of each of the thermocouples, and the infrared detecting device according to the second preferred embodiment of the present invention is characterized in that Ap/An ratio of the sectional area of the p-type polysilicon to that of the n-type polysilicon is in a range of {square root over ( )}(m) to {square root over ( )}(m)
when a gap between the p-type and n-type polysilicons is constant and &rgr;p/&rgr;n ratio of electric resistivity of the polysilicons is defined as “m” and kp/kn ratio of thermal conductivity of the polysilicons is defined as “n”.
The infrared detecting device according to the third preferred embodiment of the present invention is characterized in that the p-type and n-type polysilicons are equivalent in their thickness, and different in their width from each other at the position between the hot and cold junctions of each of the thermocouples, the infrared detecting device according to the fourth preferred embodiment of the present invention is constituted so that the p-type and n-type polysilicons are equivalent in their width, and different in their thickness from each other at the position between the hot and cold junctions of each of the thermocouples, the infrared detecting device according to the fifth preferred embodiment of the present invention is constituted so that Wp/Wn ratio of the width of the p-type polysilicon to that of the n-type polysilicon is in a range of {square root over ( )}(m) to {square root over ( )}(m)
when a gap between the p-type and n-type polysilicons is constant, the p-type and n-type polysilicons are equivalent in their thickness, &rgr;p/&rgr;n ratio of electric resistivity of the polysilicons is defined as “m” and kp/kn ratio of thermal conductivity of the polysilicons is defined as “n”, and the infrared detecting device according to the sixth preferred embodiment of the present invention is characterized in that tp/tn ratio of the thickness of the p-type polysilicon to that of the n-type polysilicon is in a range of {square root over ( )}(in) to {square root over ( )}(m)In when a gap between the p-type and n-type polysilicons is constant, the p-type and n-type polysilicons are equivalent in their width, &rgr;p/&rgr;n ratio of electric resistivity of the polysilicons is defined as “m” and kp/kn ratio of thermal conductivity of the polysilicons is defined as “n”.
The infrared detecting device according to the seventh preferred embodiment of the present invention is characterized in that ratio of width of polysilicon with high thermal conductivity to that of polysilicon with low thermal conductivity is maximized when the number of the thermocouples and a gap between the p-type and n-type polysilicons are constant, and the polysilicons are equivalent in their thickness.
REFERENCES:
patent: 4032363 (1977-06-01), Raag
patent: 5100479 (1992-03-01), Wise et al.
patent: 6163061 (2000-12-01), Iida
patent: 11051762 (1999-02-01), None
“Infrared thermopile sensors with high sensitivity and very low temperature coefficient”, J. Schieferdecker, R. Quad, E. Holzenkämpfer, M. Schulze, Sensors and Actuators A, Elsevier Sequoia S.A., Lausanne, CH, 1995, pp. 422-427.
Morita Shin-ichi
Shibata Nami
IHI Aerospace Co., Ltd.
Kalafut Stephen
Parsons Thomas H.
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