Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-08-28
2004-04-06
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S332000
Reexamination Certificate
active
06717147
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a thermo-sensitive infrared ray detector and, more particularly, to a thermo-sensitive infrared ray detector having a thermal isolation structure.
(b) Description of the Related Art
A thermo-sensitive infrared ray detector is generally used for detecting the temperature of an object by detecting infrared rays radiated from the object.
The thermo-sensitive infrared ray detector absorbs infrared rays radiated from the object at an infrared ray absorption film, installed therein and having an optical resonator structure, to convert infrared rays into heat. The heat generated by the conversion raises the temperature of a thermo-sensitive resistor, such as a bolometer film, forming a diaphragm having a micro bridge structure. The temperature of the object can be detected by the increase of the resistance of the thermo-sensitive resistor or bolometer film.
The thermo-sensitive infrared ray detector having such a thermal isolation structure generally involves a drift in the output signal due to a fluctuation of the ambient temperature, because it detects the infrared ray by measuring the temperature change of the bolometer film itself. The drift prevents an accurate measurement of the infrared ray by the thermo-sensitive infrared ray detector (hereinafter, may be referred to as simply “infrared ray detector”).
For suppression of the drift in the output signal of the infrared ray detector caused by the fluctuation of the ambient temperature, it may be considered that a temperature control unit is associated with the infrared ray detector. However, this raises the cost of the infrared ray detector. A technique obviating the use of the temperature control unit is described in, for example, Patent Publications JP-A-11-248530 and -10-227689.
FIG. 1
shows the structure of the infrared ray detector described in JP-A-11-248530, and
FIG. 2
shows the schematic circuit diagram of the amplifier disposed therein. The infrared ray detector includes an array of pixels formed on a substrate
82
, each of the pixels including a metal bolometer
80
, and a resistor
83
made of a material same as the material of the metal bolometer
80
and embedded in the substrate
82
. The thermal isolation structure wherein the metal bolometer
80
is supported by a pair of struts
81
for thermal isolation of the metal bolometer
80
from the substrate
82
allows the metal bolometer
80
to change the resistance thereof upon irradiation of an infrared ray. On the other hand, the resistor
83
embedded in the substrate
82
exhibits a little temperature change upon the irradiation of the infrared ray.
The operational amplifier or inverting amplifier
84
having the resistor
83
as an input resistance (Rs) and the metal bolometer
80
as a feedback resistor (Rf) outputs a voltage signal representing a resistance ratio R
F
/R
S
. This configuration, wherein the resistance of the resistor
83
is used as a reference value, allows the cancellation of the fluctuation of the ambient temperature from the output of the metal bolometer
80
, whereby installation of a temperature control unit is obviated in the infrared ray detector. In addition, since both the metal bolometer
80
and the resistor
83
are formed by using a thin film technique, the difference in the physical property between the metal bolometer
80
and the resistor
83
can be made minimum to thereby improve the accuracy of the measurement.
FIG. 3
shows a read circuit used in the infrared ray detector described in JP-A-10-227689, wherein the read circuit includes a chopper amplifier. The infrared ray detector includes in a single pixel a first thermo-sensitive resistor
101
and a second thermo-sensitive resistor
102
which constitutes a dummy resistor. The chopper amplifier includes first switch
104
a
, second switch
104
b
, third switch
104
c
, a capacitor
106
and an inverter
107
.
The first thermo-sensitive resistor
101
and the dummy resistor
102
are connected to a current mirror
103
, whereby the same current flows through the first thermo-sensitive resistor
101
and the dummy resistor
102
. After the first switch
104
a
is activated (or closed) while both the resistors
101
and
102
pass the current, the output signal on a first node
105
a
is transmitted to one of the terminals of the capacitor
106
, the other of the terminals of which is connected to the input of the inverter
107
through a second node
105
b
. By supplying a clock signal to activate the second switch
104
b
when the capacitor
106
receives the signal, the input and the output of the inverter are short-circuited, determining the operational point of the amplifier.
Thereafter, the first and second switches
104
a
and
104
b
are made open and the clock signal is supplied to the third switch
104
c
to activate the same, whereby the signal on the second node
105
b
is transmitted to the capacitor
106
. The third node
105
c
allows a potential equal to a potential difference between the first node
105
a
and the second node
105
b
to be delivered to the third node
105
c
. The potential difference between the first node
105
a
and the second node
105
b
corresponds to the temperature rise which corresponds to the amount of the infrared ray irradiation. Thus, the signal on the third node
105
c
is delivered from the amplifier through the inverter
107
.
FIG. 4
shows the infrared ray detector described in JP-A-10-227689, wherein a thermo-sensitive resistor
121
including a first bolometer film
131
and a dummy resistor
122
including a second bolometer film
132
are juxtaposed on a silicon substrate
123
in each pixel. The first bolometer film
131
is thermally isolated from the silicon substrate
123
by a cavity
126
disposed therebetween and formed by using a micro-machining technique, whereby the first thermo-sensitive resistor
121
is susceptible to a temperature rise caused by infrared ray irradiation. The second bolometer film
132
has a shape and dimensions similar to the shape and dimensions of the first bolometer film
131
, and is located on the silicon substrate
123
via a support plate
124
.
Both the first and second bolometer films
131
and
132
have similar temperature coefficient of resistances (TCR) so that the fluctuation of the ambient temperature does not cause any substantial change of the output of the infrared ray detector. The support plate
124
of the second bolometer film
132
may have small thickness as shown in
FIG. 4
or may have a larger thickness as shown in
FIG. 5
, which shows a modification of the infrared ray detector of FIG.
4
.
In the infrared ray detector shown in
FIG. 4
or
5
, if the second bolometer film
132
is irradiated by an infrared ray, the heat generated by the infrared ray irradiation in the second bolometer film
132
is readily transferred to the silicon substrate
123
acting as a heat sink, whereby the resistance of the second bolometer film
132
is not changed by the infrared ray irradiation. More specifically, the second bolometer film
132
is susceptible only to the fluctuation of the ambient temperature whereas the second bolometer film
131
is susceptible to both the infrared ray irradiation and the fluctuation of the ambient temperature. By combining this configuration with the signal read circuit of
FIG. 2
, while a DC output voltage component is made constant irrespective of the ambient temperature, the signal component caused by the infrared ray irradiation is superimposed on the DC output voltage component.
In both the conventional infrared ray detectors, as described above, although the metal bolometer
80
and the first bolometer film
131
are thermally isolated from the substrates
82
and
123
, respectively, the dummy resistor
83
and the second bolometer film
132
are disposed substantially directly on the substrate acting as a heat sink. This configuration allows the fluctuation of the ambient temperature to be cancelled by using the output difference as described a
Hannaher Constantine
Moran Timothy J.
NEC Corporation
Young & Thompson
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