Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1998-09-03
2001-03-06
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338400, C250S342000, C338S018000
Reexamination Certificate
active
06198099
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an infra-red bolometer; and, more particularly, to the infra-red bolometer having an absorber with a reflective layer formed at the bottom surface thereof.
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
FIG. 1
, there is a cross sectional view setting forth two-level microbridge bolometer
100
, disclosed in U.S. Pat. No. 5,286,976 and entitled “MICROSTRUCTURE DESIGN FOR HIGH IR SENSITIVITY”, the bolometer
100
including a lower level
111
, an elevated microbridge detector level
112
and sloping supports
130
. There exists a thermal isolation cavity or air gap
126
.
The lower level
111
includes a flat surfaced semiconductor substrate
113
, an integrated circuit
115
, a protective layer
116
and a thin film reflective layer
118
. The substrate
113
is formed as a single crystal silicon substrate. The surface
114
of the substrate
113
has fabricated thereon conventional components of the integrated circuit
115
. The integrated circuit
115
is coated with the protective layer of silicon nitride
116
. The reflective layer
118
made of a metal, e.g., Pt or Au, is formed on top of the protective layer
116
.
The elevated detector level
112
includes a silicon nitride layer
120
, a thin film resistive layer
121
of vanadium or titanium oxide (V
2
O
3
, TiO
x
, VO
x
), a silicon nitride layer
122
over the layers
120
and
121
and IR absorber coating
123
over the silicon nitride layer
122
. The material chosen for the thin film resistive layer
121
are characterized by a low IR reflectance together with a relatively high temperature coefficient of resistance (TCR). The IR absorber coating may be made of a Permalloy, e.g., a nickel iron alloy. Downwardly extending silicon nitride layers
120
′ and
122
′ formed at the same time as the layers
120
and
122
during make up the sloping supports
130
for the elevated detector level
112
. The ends of the resistive layer
121
also continued down the sloping supports
130
embedded in
120
′ and
22
′ to make electrical contact with the lower level
111
. During the fabrication process, however, the cavity
126
was originally filled with a previously deposited layer of easily dissolvable glass or other dissolvable material, e.g., quartz, polyamide and resist, until the layers
120
,
120
′,
122
and
122
′ were deposited. Subsequently in the process the glass was dissolved out to provide the cavity or gap
126
.
The optical properties of the bolometer
100
are achieved by the determination of the total structure. To optimize the absorption in the structure, the thickness of all the absorbing layers and the air gap distance must be controlled. In this two-level structure, the elevated detector level
112
is separated from the reflective layer
118
by the air gap. The interference properties of the reflected radiation are such that significant absorption is achieved by the range of wavelengths and air gap spacing between the reflective layer
118
and the elevated detector level
112
. The detectors presently being described are intended for use in the 8-14 micron IR wavelength. As an effect of experimentation in the wavelength 8-14 microns, with air gaps of 1-2 microns and especially at 1.5 microns the absorption is relatively high across the desired wavelength spread.
The effect of gap thickness of the absorption vs. wavelength in the regions of interest are further displayed graphically in FIG.
2
. It can be seen in the curve of 1.5 microns gap thickness that at 8 microns the absorption of the structure is climbing rapidly, and that is remains relatively high out to about 14 microns. The curve for a gap of 2 microns shows that at IR wavelengths of 14 microns the absorption is better.
There are certain deficiencies associated with the above bolometer
100
. The air gap size has to be determined though experimentations with considerations given to the incident IR wavelength relative to the object for using the bolometer
100
and this is an extremely difficult and heavy task. Furthermore, in the manufacture of the bolometer
100
, the fabricating condition for easily dissolvable glass material, with which the air gap is filled, changes according to the determined gap size, which will, in turn, make a mass production of the bolometer
100
difficult.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide an infra-red bolometer including an absorber with a reflecting layer formed at the bottom surface thereof.
In accordance with one aspect of the present invention, there is provided an 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 formed on top thereof, wherein the conduction line is electrically connected to the connecting terminal; an absorption level including an absorber with a reflective layer attached at bottom surface thereof, a serpentine bolometer element surrounded by the absorber and an IR absorber coating formed on top of the absorber; 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, wherein top end of the electrical conduit is connected to one end of the bolometer element and bottom end of the electrical conduit is connected to the connection line.
REFERENCES:
patent: 3415994 (1968-12-01), Fitti, Jr.
patent: 4922116 (1990-05-01), Grinberg et al.
patent: 5010251 (1991-04-01), Grinberg et al.
patent: 5021663 (1991-06-01), Hornbeck
patent: 5054936 (1991-10-01), Fraden
patent: 5286976 (1994-02-01), Cole
patent: 5300915 (1994-04-01), Higashi et al.
patent: 5302933 (1994-04-01), Kude et al.
patent: 5426412 (1995-06-01), Tomonari et al.
patent: 5584117 (1996-12-01), Lee et al.
patent: 5760398 (1998-06-01), Blackwell et al.
patent: 5811815 (1998-09-01), Marshall et al.
patent: 5831266 (1998-11-01), Jerominek et al.
patent: 5939971 (1999-08-01), Yong
patent: 0354369 (1990-02-01), None
patent: 10111178 (1998-04-01), None
patent: WO 9401743 (1994-01-01), None
PCT International Search Report, Aug. 31, 1998, PCT/KR 98/00267.
Daewoo Electronics Co. Ltd.
Ham Seungsook
Patti John
Pennie & Edmonds LLP
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