Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-09-03
2001-03-13
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338400, C338S018000
Reexamination Certificate
active
06201244
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an infra-red bolometer; and, more particularly, to a three-level infra-red bolometer including an absorber made of a material having a low deposition-temperature and a low heat-conductivity.
BACKGROUND OF THE INVENTION
Bolometers are energy detectors based upon a change in the resistance of materials (called bolometer elements) that are exposed to a radiation flux. The bolometer elements have been made from both metals and semiconductors. In case of the metals, the resistance change is essentially due to a variation in the carrier mobility, which typically decreases with temperature. In contrast, greater sensitivity can be obtained in high-resistivity semiconductor bolometer elements wherein the free-carrier density is an exponential function of temperature; however, thin film fabrication of semiconductor elements for the construction of bolometers is a difficult task.
In
FIGS. 1 and 2
, there are shown a perspective view and a cross sectional view illustrating a three-level bolometer
100
, disclosed in U.S. application Ser. No. 09/102,364 entitled “BOLOMETER HAVING AN INCREASED FILL FACTOR”. The bolometer
100
comprises an active matrix level
110
, a support level
120
, at least a pair of posts
170
and an absorption level
130
.
The active matrix level
110
has a substrate
112
including an integrated circuit (not shown), a pair of connecting terminals
114
and a protective layer
116
. Each of the connecting terminals
114
made of a metal is located on top of the substrate
112
. The protective layer
116
made of, e.g., silicon nitride (SiN
x
), covers the substrate
112
. The pair of connecting terminals
114
are electrically connected to the integrated circuit.
The support level
120
includes a pair of bridges
140
made of silicon nitride (SiN
x
), each of the bridges
140
having a conduction line
165
formed on top thereof. Each of the bridges
140
is provided with an anchor portion
142
, a leg portion
144
and an elevated portion
146
, the anchor portion
142
including a via hole
152
through which one end of the conduction line
165
is electrically connected to the connecting terminal
114
, the leg portion
144
supporting the elevated portion
146
.
The absorption level
130
is provided with a serpentine bolometer element
185
made of titanium (Ti), an absorber
195
made of silicon nitride (SiN
x
) and an IR absorber coating
197
formed on top of the absorber
195
. The absorber
195
is fabricated by depositing silicon nitride before and after the formation of the serpentine bolometer element
185
to surround the serpentine bolometer element
185
.
Each of the posts
170
is placed between the absorption level
130
and the support level
120
. Each of the posts
170
includes an electrical conduit
172
made of a metal, e.g., titanium (Ti), and surrounded by an insulating material
174
made of, e.g., silicon nitride (SiN
x
). Top end of the electrical conduit
172
is electrically connected to one end of the serpentine bolometer element
185
and bottom end of the electrical conduit
172
is electrically connected to the conduction line
165
on the bridge
140
, in such a way that both ends of the serpentine bolometer element
185
in the absorption level
130
is electrically connected to the integrated circuit of the active matrix level
110
through the electrical conduits
172
, the conduction lines
165
and the connecting terminals
114
. When exposed to infra-red radiation, the resistivity of the serpentine bolometer element
185
changes, causing a current and a voltage to vary, accordingly. The varied current or voltage is amplified by the integrated circuit, in such a way that the amplified current or voltage is read out by a detective circuit (not shown).
There are certain deficiencies associated with the above described three-level bolometer
100
. When selecting the material for the absorber
195
, it is important to consider the fabrication conditions, e.g., deposition-temperature, and the material characteristics, e.g., heat-conductivity. In the above described three-level bolometer
100
, since silicon nitride (SiN
x
) can be formed only at a relatively high temperature, e.g., over 850° C., titanium (Ti) constituting the serpentine bolometer element
185
gets easily oxidized during the formation of the absorber
195
, which will, in turn, detrimentally affect the temperature coefficient of resistance (TCR) thereof. Further, silicon nitride (SiN
x
) has a relatively high heat-conductivity, reducing the thermal isolation effect of the absorber
195
in the bolometer
100
.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a three-level infra-red bolometer including an absorber made of a material that can be formed at a low temperature and has a low heat-conductivity.
In accordance with one aspect of the present invention, there is provided a three-level infra-red bolometer, which comprises: an active matrix level including a substrate and at least a pair of connecting terminals; a support level provided with at least a pair of bridges, each of the bridges including an conduction line, one end of the conduction line being electrically connected to the respective connecting terminal; an absorption level including a bolometer element formed between an upper absorber and a lower absorber, the absorbers being made of silicon oxide or silicon oxy-nitride; and at least a pair of posts, each of the posts being placed between the absorption level and the support level and including an electrical conduit surrounded by an insulating material, each end of the bolometer element of the absorption level being electrically connected to the respective connecting terminal through the respective electrical conduit and the respective conduction line.
REFERENCES:
patent: 5021663 (1991-06-01), Hornbeck
patent: 5286976 (1994-02-01), Cole
patent: 5397897 (1995-03-01), Komatsu et al.
patent: 5404125 (1995-04-01), Mori et al.
patent: 5572029 (1996-11-01), Walker et al.
patent: 5629521 (1997-05-01), Lee et al.
patent: 5760398 (1998-06-01), Blackwell et al.
patent: 5789753 (1998-08-01), Gooch et al.
patent: 5811815 (1998-09-01), Marshall et al.
patent: 5939971 (1999-08-01), Yong
patent: 6028312 (2000-02-01), Wadsworth et al.
patent: 6034374 (2000-03-01), Kimura et al.
patent: 0534768 (1993-03-01), None
International Search Report Apr. 9, 1999.
Ju Sang-Baek
Yong Yoon-Joong
Daewoo Electronics Co. Ltd.
Hannaher Constantine
Pennie & Edmonds LLP
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