Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-11-19
2004-08-17
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S330000
Reexamination Certificate
active
06777680
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. For example, a thermopile infrared detecting device includes the types shown in
FIGS. 2 and 3
.
In the case of thermopile infrared detecting devices S
1
and S
2
shown in
FIGS. 2 and 3
, a diaphragm
102
is formed on a silicon (Si) substrate
101
and p-type polysilicon
110
and n-type polysilicon
111
are alternately connected by an aluminum (Al) wiring
112
to form a pair of thermocouples
113
on the diaphragm
102
. The thermocouples
113
are arranged in parallel by using the substrate
101
as a cold junction and a heat absorption area
105
as a hot junction and electrically connected in series to form thermopiles. Moreover, the heat absorption area
105
is formed on the diaphragm
102
in which the thermopiles are arranged through an insulation layer
103
. In this case, the heat absorption area
105
is present at the center of the device. Moreover, thermoelectromotive forces of the infrared detecting devices S
1
and S
2
are decided by the temperature difference between the heat absorption area
105
and the substrate
101
. The temperature difference depends on the magnitude of the thermal resistance from an end of the heat absorption area
105
up to ends of cavities
106
A and
106
B of the substrate
101
.
The cavities
106
A and
106
B formed on the substrate
101
thermally separate the cold junction side of the thermocouples
113
from the hot junction side of them. In the case of the infrared detecting device S
1
shown in
FIG. 2
, the cavity
106
A is formed by applying anisotropic etching to silicon from the back of the substrate
101
and thereby leaving the outer periphery of the device like a frame. In the case of the infrared detecting device S
2
shown in
FIG. 3
, the quadrangular-pyramidal cavity
106
B opening at the upper side of the substrate
101
below the diaphragm
102
is formed by forming an etching aperture
107
at four corners of the diaphragm
102
and then applying anisotropic etching to silicon.
In the case of the above conventional infrared detecting devices S
1
and S
2
, however, when forming the cavity
106
A (
FIG. 2
) by leaving the outer periphery of the device like a frame, it is necessary to etch a volume equal to or more than a necessary volume of the substrate
101
. Therefore, the etching time, that is, the time in which the substrate
101
is exposed to an etching solution is increased and thereby, a protective film such as the insulation layer
103
or the like is damaged. Moreover, to improve the output of the device, it is necessary to increase the heat absorption energy, that is, the area of the device. However, it is difficult to support the structural strength of the large-area device only by the diaphragm
102
. Therefore, it is attempted to form a device by using means for increasing the thickness of the diaphragm
102
or means for moderating the stress of each layer. However, even when using these means, it is difficult to completely secure the structural strength of the device and moreover, a problem occurs that the sensitivity of the device is deteriorated by increasing the thickness of the diaphragm
102
.
Moreover, in the case of forming the cavity
106
B by forming the etching aperture
107
at four corners of the diaphragm
102
(FIG.
3
), it is possible to support most of the structural strength of the device by the silicon substrate
101
and many problems do not occur in the structural strength of the device because of etching away only a part of the upper face of the substrate
101
. However, because sizes of the etching apertures
107
are restricted, the distance between the etching apertures
107
is restricted by the thickness of the substrate
101
, and positions of the etching apertures
107
are restricted to the outer periphery of the substrate
101
, it is difficult to apply the case to a device having a dimension larger than the thickness of the substrate
101
and realize a high-output device for increasing heat absorption energy.
That is, the conventional infrared detecting devices S
1
and S
2
have a problem that it is difficult to increase areas of the devices in order to increase outputs of them. Thus, it is necessary to solve the problem.
SUMMARY OF THE INVENTION
The present invention is made to solve the above conventional problem and its object is to provide a large-area high-output infrared detecting device.
The infrared detecting device according to the present invention is characterized in that a heat-separation-structure diaphragm made of a thermal insulating material is formed through cavities from a silicon substrate, an infrared detection section is formed on the diaphragm, a heat absorption area is formed on the infrared detection section through an insulation layer, and an etching aperture for forming cavities is formed in the heat absorption area, the infrared detecting device according to a preferred embodiment of the present invention has a configuration in which a plurality of etching apertures are formed in the heat absorption area, the infrared detecting according to another embodiment of the present invention has a configuration in which the plurality of etching apertures are formed in the heat absorption area at equal intervals, the infrared detecting device according to the other embodiment of the present invention has a configuration in which a plurality of etching apertures are also formed on the diaphragm other than the heat absorption area, the infrared detecting device according to further embodiment of the present invention has a configuration in which the cavity is formed through anisotropic etching, and the infrared detecting device according to the other preferred embodiment of the present invention has a configuration in which the infrared detecting device is a thermopile type. The above configurations serve as means for solving the conventional problem.
In the case of the above configurations, when forming one etching aperture in a heat absorption area, it is preferable to form the etching aperture at the center of the heat absorption area. When fabricating the device concerned, cavities are formed on a silicon substrate by applying anisotropic etching to the substrate through the etching aperture to control depths of the cavities in accordance with the etching time. Moreover, in the case of the configuration having a plurality of etching apertures in a heat absorption area at equal intervals, it is preferable to properly set sizes of and the interval between etching apertures in accordance with the size of a cavity to be formed and the etching time of the cavity. In this case, etching can be optimized by setting a plurality of etching apertures at equal intervals. However, when the etching time to be set has an allowance, it is not always necessary to set the etching apertures at equal intervals. Moreover, in the case of the configuration in which a diaphragm is formed on a substrate, it is possible to form a sacrifice layer made of polymer or polysilicon in a proper thickness between the substrate and the diaphragm. When fabricating the device concerned, it is possible to form cavities by applying isotropic etching to a sacrifice layer and then applying anisotropic etching to a silicon substrate. According to the infrared detecting device of the present invention, because an etching aperture is formed in a heat absorption area of the infrared detecting device, it is possible to apply anisotropic etching to a silicon substrate through the etching aperture, form almost-concave cavities opening at the heat absorption area side on the substrate, fabricate an infrared detecting device having an area larger than the thickness of the substrate, form substrate cavities for thermally separating the cold junction of a thermopile from the hot junction of it independently of the size of the heat abso
Morita Shin-ichi
Shibata Nami
Hannaher Constantine
IHI Aerospace Co., Ltd.
Moran Timothy
LandOfFree
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