Infrared bolometer

Details Infrared bolometer Infrared bolometer

1998-12-29

2001-07-17

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S332000, C250S338400

Reexamination Certificate

active

06262417

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an infrared bolometer; and, more particularly, to the infrared bolometer capable of preventing a post therein from becoming tilted.
BACKGROUND OF THE INVENTION
A radiation detector is a device that produces an output signal which is a function of the amount of radiation that is incident upon an active region of the detector. Infra-red detectors are those detectors which are sensitive to radiation in the infra-red region of the electromagnetic spectrum. There are two types of infra-red detectors, thermal detectors including bolometers and photon detectors.
The photon detectors function based upon the number of photons that are incident upon and interact with electrons in a transducer region of the detector. The photon detectors, since they function based on direct interactions between electrons and photons, are highly sensitive and have a high response speed compared to the bolometers. However, they have a shortcoming in that the photon detectors operate well only at low temperatures, necessitating a need to an incorporate therein an additional cooling system.
The bolometers function, on the other hand, based upon a change in the temperature of the transducer region of the detector due to absorption of the radiation. The bolometers provide an output signal, i.e., a change in the resistance of materials (called bolometer elements), that is proportional to the temperature of the transducer region. The bolometer elements have been made from both metals and semiconductors. In metals, the resistance change is essentially due to variations in the carrier mobility, which typically decreases with temperature. Greater sensitivity can be obtained in high-resistivity semiconductor bolometer elements in which the free-carrier density is an exponential function of temperature.
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
10
, a support level
20
, a pair of posts
40
and an absorption level
30
.
The active matrix level
10
has a substrate
12
including an integrated circuit (not shown), a pair of connecting terminals
14
and a protective layer
16
. Each of the connecting terminals
14
made of a metal is located on top of the substrate
12
. The protective layer
16
made of, e.g., silicon nitride (SiN
x
) , covers the substrate
12
. The pair of connecting terminals
14
are electrically connected to the integrated circuit.
The support level
20
includes a pair of bridges
22
made of silicon nitride (SiN
x
) , each of the bridges
22
having a conduction line
24
formed on top thereof. Each of the bridges
22
is provided with an anchor portion
22
a
, a leg portion
22
b
and an elevated portion
22
c
, the anchor portion
22
a
including a via hole
26
through which one end of the conduction line
24
is electrically connected to the connecting terminal
14
, the leg portion
22
b
supporting the elevated portion
22
c .
The absorption level
30
is provided with a bolometer element
32
surrounded by an absorber
31
and an IR absorber coating
33
formed on top of the absorber
31
. The absorber
31
is fabricated by depositing silicon nitride before and after the formation of the bolometer element
32
to surround the bolometer element
32
. Titanium (Ti) is chosen as the material for bolometer element
32
because of the ease with which it can be formed. Serpentine shape gives the bolometer element
32
to high resistivity.
Each of the posts
40
is placed between the absorption level
30
and the support level
20
. Each of the posts
40
includes an electrical conduit
42
made of a metal, e.g., titanium (Ti), and surrounded by an insulating material
44
made of, e.g., silicon nitride (SiN
x
) Top end of the electrical conduit
42
is electrically connected to one end of the serpentine bolometer element
32
and bottom end of the electrical conduit
42
is electrically connected to the conduction line
24
on the bridge
22
, in such a way that each ends of the serpentine bolometer element
32
in the absorption level
30
is electrically connected to the integrated circuit of the active matrix level
10
through the electrical conduits
42
, the conduction lines
24
and the connecting terminals
14
.
When exposed to infra-red radiation, the resistivity of the serpentine bolometer element
32
increases, 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).
In the above-described infrared bolometer, in order to decrease the thermal exchange between the active matrix level and the absorption level, the support level is as long as possible, and this is achieved by cantilevering the support level on the active matrix level. This solution, however, has a drawback in that the elevated portion of the bridge gets warped easily and bent upward to relieve the elastic stress accumulated in the bridge during the formation thereof, which will, in turn, bend the absorber, resulting in decreasing the absorbing efficiency of the bolometer.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide an infrared bolometer capable of preventing a post therein from being tilted.
In accordance with one aspect of the present invention, there is provided the infra-red bolometer, which comprises: an active matrix level including a substrate and a pair of connecting terminals; a support level provided with a pair of bridges and a pair of conduction lines, whereby each of the bridges is provided with an anchor portion, a leg portion and an elevated portion, the anchor portion being affixed to the active matrix level and the elevated portion being apart from the active matrix level, wherein the elevated portion of each of the bridges includes an inner part cantilevered from an outer part; an absorption level including a bolometer element surrounded by an absorber; and a pair of posts positioned on top of the inner part of the bridge, each of the posts including an electrical conduit, wherein each ends of the bolometer element is electrically connected to the respective connecting terminal through the respective conduit and the respective conduction line.


REFERENCES:
patent: 5367167 (1994-11-01), Keenan
patent: 6094127 (2000-07-01), Yong
patent: 354396 (1990-02-01), None
patent: 111178 (1998-04-01), None
International Search Report.

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