Batteries: thermoelectric and photoelectric – Thermoelectric – Thermopile
Reexamination Certificate
2000-04-10
2002-01-15
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Thermopile
Reexamination Certificate
active
06339187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to infrared sensors and to methods of manufacturing the same. In particular, the present invention relates to a thermoelectric infrared sensor having a diaphragm structure which is prepared by etching a sacrificial layer on a semiconductor substrate or under a thin film and to a method for making the same.
2. Description of the Related Art
FIGS. 1A and 1B
are a plan view and a cross-sectional view, respectively, of a typical conventional thermoelectric infrared sensor
1
. In the thermoelectric infrared sensor
1
, a thermal insulating thin film
4
is provided on a heat sink frame
2
and a cavity section
3
, and two types of metals or semiconductors
5
and
6
are alternately wired on the central portion of the thermal insulating thin film
4
to form a thermopile
9
comprising thermocouples connected in series. These metals or semiconductors
5
and
6
are connected at portions above the heat sink frame
2
to form cold junctions
7
of the thermocouples, and are also connected at portions above the cavity section
3
to form hot junctions
8
of the thermocouples. The cold and hot junctions are formed on the thermal insulating thin film
4
. The thermopile
9
has external electrodes
11
at both ends. The hot junctions
8
are covered with an infrared-absorbing layer
10
.
Infrared rays incident on the thermoelectric infrared sensor
1
are absorbed in the infrared-absorbing layer
10
to generate heat which is conducted to the hot junctions
8
. Thus, a temperature difference is generated between the cold junctions
7
and hot junctions
8
formed above the heat sink
2
, which produces an electromotive force between the external electrodes
11
of the thermopile
9
. Suppose that the thermoelectromotive force generated at a junction (or a thermocouple) of two metals or semiconductor elements
5
or
6
at a temperature of T is represented by &PHgr;(T), and the number of the hot junctions
8
and the cold junctions
7
is m, respectively. When the temperature at the hot junctions
8
is T
W
and the temperature at the cold junctions
7
is T
C
, the electromotive force V generated between the external electrodes
11
of the thermopile
9
is represented by equation (1):
V=m[&PHgr;(T
W
)−&PHgr;(T
C)]
(1)
When the temperature T
C
at the heat sink frame
2
is known, the temperature T
W
at the hot junctions
8
is determined from the electromotive force V generated between the external electrodes
11
. Since the temperature of the infrared-absorbing layer
10
increases according to the dose of the infrared rays which are incident on the infrared sensor
1
and are absorbed in the infrared-absorbing layer
10
, the dose of the infrared rays incident on the infrared sensor
1
can be determined by measuring the temperature T
W
at the hot junctions
8
.
In general, in such an infrared sensor
1
, the heat sink frame
2
is comprised of a silicon substrate and the heat insulating film
4
is composed of SiO
2
film having a low thermal conductivity. The SiO
2
film, however, has high compressive stress. When the heat insulating film
4
is formed of a single SiO
2
layer, the heat insulating film
4
may break in some cases.
Thus, in another conventional infrared sensor
12
shown in
FIG. 2
, a heat insulating film
4
on a silicon heat sink frame
2
comprises a Si
3
N
4
layer
13
, a SiO
2
layer
14
, and a Si
3
N
4
layer
15
, a thermopile
9
is covered with a protective film
16
, and an infrared-absorbing layer
10
is provided thereon. In this configuration, the Si
3
N
4
layers
13
and
15
have tensile stress and the SiO
2
layer
14
has compressive stress. Thus, the stress of the heat insulating film
4
formed by laminating these layers is relaxed to avoid damage to the heat insulating film
4
.
Since the Si
3
N
4
layers
13
and
15
are formed by a low pressure CVD (LPCVD) process, the heat insulating film
4
composed of the Si
3
N
4
layers
13
and
15
and the SiO
2
layer
14
is produced at high facility and production costs. As a result, the infrared sensor
12
is inevitably expensive.
In another infrared sensor
17
shown in
FIG. 3
, a heat insulating film
4
on a heat sink frame
2
is a multilayered film composed of SiO
2
layers and Al
2
O
3
layers which are formed by an ion plating process. Also, in such a configuration, the tensile stress of the Al
2
O
3
layers offsets the compressive stress of the SiO
2
layers to avoid damage to the heat insulating film
4
.
Since the Al
2
O
3
films have a high thermal conductivity, the heat generated by the infrared rays in an infrared-absorbing layer
10
dissipates to the heat sink frame
2
via the Al
2
O
3
layers. Thus, an increase in the temperature at the hot junctions is suppressed. Accordingly, the sensitivity of the infrared sensor
17
is reduced.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an infrared sensor which can be produced at reduced production costs and which exhibits high sensitivity.
It is another object of the present invention to provide a method for manufacturing the infrared sensor.
According to an aspect of the present invention, an infrared sensor comprises a heat insulating thin-film, a heat sink section for supporting the heat insulating thin-film, and a thermoelectric infrared detecting element provided on the heat insulating thin-film, wherein the heat insulating thin-film comprises an insulating layer primarily composed of aluminum oxide having partial oxygen defects and a silicon oxide layer. The thermoelectric infrared detecting element converts thermal energy into electrical energy. Examples of such elements include thermopiles (thermocouples), pyroelectric elements, and bolometers.
Since the insulating layer primarily composed of aluminum oxide having partial oxygen defects exhibits tensile stress and a low thermal conductivity, the aluminum oxide insulating layer offsets the compressive stress of the silicon oxide layer which is another constituent of the heat insulating thin-film. Thus, the heat insulating thin-film exhibits a low thermal conductivity and is barely damaged. Accordingly, this infrared sensor has high mechanical strength and high sensitivity. The aluminum oxide having partial oxygen defects can be readily formed by a vacuum deposition process at reduced facility and production costs.
In this infrared sensor, the aluminum oxide having partial oxygen defects is preferably represented by equation (2):
Al
2
O
3−X
(2)
wherein the subscript X indicates the rate of the oxygen defects and is within a range of 0.05≦X≦0.5.
When X is outside of this range, the thermal conductivity of the aluminum oxide insulating layer increases.
According to another aspect of the present invention, an infrared sensor comprises a heat insulating thin-film, a heat sink section for supporting the heat insulating thin-film, and a thermoelectric infrared detecting element provided on the heat insulating thin-film, wherein the heat insulating thin-film comprises an insulating layer primarily composed of amorphous aluminum oxide and a silicon oxide layer.
Since the insulating layer primarily composed of amorphous aluminum oxide exhibits tensile stress and a low thermal conductivity, the amorphous aluminum oxide insulating layer offsets the compressive stress of the silicon oxide layer which is another constituent of the heat insulating thin-film. Thus, the heat insulating thin-film exhibits a low thermal conductivity and is barely damaged. Accordingly, this infrared sensor has high mechanical strength and high sensitivity. The amorphous aluminum oxide can be readily formed by a vacuum deposition process at reduced facility and production costs.
According to another aspect of the present invention, a method for making an infrared sensor comprises supporting a heat insulating thin-film comprising a silicon oxide layer and an aluminum oxide layer with a heat sink section, and providing a the
Gorgos Kathryn
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
Parsons Thomas H
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