Bolometer with a serpentine stress balancing member

Details Bolometer with a serpentine stress balancing member Bolometer with a serpentine stress balancing member

1998-09-03

2001-05-01

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S332000, C338S018000

Reexamination Certificate

active

06225629

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an infra-red bolometer; and, more particularly, to the infra-red bolometer incorporating therein a serpentine stress balancing member.
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 bolometer
100
, the bolometer
100
including 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 insulating material, e.g., silicon oxide, each of the bridges
140
having a conduction line
165
formed on top thereof. One end of the conduction line
165
is electrically connected to the respective connecting terminal
114
through a via hole
155
.
The absorption level
130
is provided with a bolometer element
185
made of titanium (Ti), an absorber
195
made of insulating material, e.g., silicon oxide (SiO
2
) or silicon oxy-nitride (SiO
x
N
y
) and an IR absorber coating
197
formed on top of the absorber
195
. The bolometer element
185
has a serpentine shape for increasing its resistivity.
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 oxide (SiO
2
) or silicon oxy-nitride (SiO
x
N
y
). 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 shortcomings associated with the above described the infra-red bolometer
100
. For example, since the absorption level
130
is structurally asymmetric, that is, the length of bolometer element
185
formed in row direction is different from that of bolometer element
185
formed in column direction, compression stress built up inside the absorber
195
gets unevenly distributed, bending the absorber
195
in one direction, as shown in
FIG. 3
, which will, in turn, reduce the overall absorption efficiency of the infra-red bolometer
100
decreases.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide an infra-red bolometer including a serpentine stress balancing member to counter the effect of the unevenly distributed compressive stress inside an absorber.
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, one end of the conduction line being electrically connected to the respective connecting terminal; an absorption level including a stress balancing member, an absorber and a bolometer element; 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.


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International Search Report Apr. 14, 1999, EPO.

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