Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-09-15
2002-12-03
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S332000
Reexamination Certificate
active
06489614
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to infrared radiation detector cells for detecting infrared radiation, in particular, to thermal-type infrared radiation detector cells for detecting infrared radiation by converting it to heat, and further relates to image capture devices incorporating such thermal-type infrared radiation detector cells. Specifically, the present invention relates to thermal-type infrared radiation detector cells with an increased infrared radiation absorption rate and reduced irregularities in detection sensitivity, and further relates to image capture devices incorporating such thermal-type infrared radiation detector cells.
BACKGROUND OF THE INVENTION
Conventionally, there are a large variety of infrared radiation detection methods being developed based on different principles and adopted in the working of various types of infrared radiation detector cells for detecting infrared radiation. Typically used among these methods is to convert infrared radiation energy into electrical signals by means of a band gap of semiconductor materials, i.e., to exploit photon effects of infrared radiation energy, because the method exhibits high sensitivity and quick response. Infrared radiation detector cells incorporating the method is called a quantum type.
Despite these advantages, the quantum-type infrared radiation detector cell is only capable of detecting a limited range of wavelengths. To detect those infrared rays with very low infrared radiation energy, e.g., those with long wavelengths, semiconductor materials used for the detection of infrared radiation need to be kept at an extremely low temperature. For example, in the quantum-type infrared radiation detector cell, the semiconductor material needs to be kept around 77K, that is, approximately −196° C., using liquid nitrogen. This requirement makes infrared radiation detector devices cumbersome to handle and difficult to make smaller due to the use of liquid nitrogen for cooling.
Another type of infrared radiation detector cells developed based on different principles to detect infrared radiation is of thermal types that do so by converting infrared radiation energy into heat. In a thermal-type infrared radiation detector cell, as a detector cell material absorbs infrared radiation energy and converts it to heat, the detector cell material heats up and thus changes its physical properties (electrical resistance, pyroelectricity, etc.). By means of the detection of these changes, the infrared radiation is detected.
Accordingly, in the thermal-type infrared radiation detector cell, unlike in its quantum-type counterpart, there is no need for semiconductor materials used for the detection of infrared radiation to be kept at extremely low temperatures. Thus, the thermal-type infrared radiation detector cell can be used at room temperature and offers room for possible reduction in size through the omission of cooling means, thereby getting wide attention for its practical performance in recent years.
However, some objects generate so little heat in the thermal-type infrared radiation detector cell that the resultant temperature elevation is as small as 0.01° C. or even smaller, making it difficult for the thermal-type infrared radiation detector cell to detect infrared radiation. To solve this problem, some thermal-type infrared radiation detector cells incorporate such a structure that exhibits an increased infrared radiation absorption rate, and thus increase the elevation in their temperature and enhance the sensitivity in detecting infrared radiation to a greatest extent possible.
To solve these problems, the typical thermal-type infrared radiation detector cell typically including a diaphragm structure in which a diaphragm structural body for detecting infrared radiation is separated by a predetermined gap from a semiconductor substrate on which there is provided an integrated circuit (or a signal integrated circuit) electrically connected to the diaphragm structural body by metal wiring. The structure enhances the thermal insulation between the diaphragm structural body (infrared radiation receiving section, or sensor section) for detecting infrared radiation and the semiconductor substrate with an integrated circuit, thereby successfully achieving high sensitivity in the detection of infrared radiation.
To further improve on the infrared radiation absorption rate, the thermal-type infrared radiation detector cell incorporating the diaphragm structure normally employs one of two techniques: namely, (a) the selective use of substance exhibiting high infrared radiation absorption, and (2) the adoption of multiple reflection of infrared rays. According to technique (1), arrangement (a) is employed whereby a thin film (infrared radiation absorbing film) composed of a material exhibiting a high infrared radiation absorption rate is provided on the surface of the diaphragm structure. According to technique (2), arrangement (b) is employed whereby, in addition to arrangement (a), an infrared radiation reflector film is provided on the semiconductor substrate below the diaphragm structure.
FIGS.
15
(
a
) and
15
(
b
) show an example of arrangement. (a) adopted in a thermal-type infrared radiation detector cell incorporating technique (1). A diaphragm structural body
101
a
is positioned over a semiconductor substrate
108
on top of which there is provided an integrated circuit (not shown), so as to be separated from the semiconductor substrate
108
by a predetermined gap. An infrared radiation absorbing film
107
a
is also provided on the surface of the diaphragm structural body
101
a
(arrangement (a)).
FIGS.
16
(
a
) and
16
(
b
) show an example of arrangement (b) adopted in a thermal-type infrared radiation detector cell incorporating technique (2). Arrangement (b) is basically identical to arrangement (a) employed in the thermal-type infrared radiation detector cell shown in FIGS.
15
(
a
) and
15
(
b
), except that arrangement (b) additionally includes an infrared radiation reflector film
106
on the surface of the semiconductor substrate
108
.
The arrangements employed in the thermal-type infrared radiation detector cell will be briefly discussed below. The diaphragm structural body
101
a
or
101
b
are each constituted by a second silicon oxide film
102
, a thermally variable resistor film
103
and a metal wiring film
104
provided on the second silicon oxide film
102
in a predetermined pattern, and a third silicon oxide film
105
covering these films. Infrared radiation absorbing films
107
a
and
107
b
composed of a material processing a high infrared radiation absorption rate are provided on the third silicon oxide film
105
according to techniques (1) and (2) respectively (arrangement (a)).
A first silicon oxide film
109
is provided on the semiconductor substrate
108
on top of which there is provided an integrated circuit (not shown). According to technique (2), an infrared radiation reflector film
106
composed of a substance capable of substantially entirely reflecting infrared rays is provided on the first silicon oxide film
109
so as to oppositely face the diaphragm structural body
101
b
(arrangement (b)).
It should be noted that as shown in
FIG. 15
(
a
) and FIG.
16
(
a
), both diaphragm structural bodies
101
a
and
101
b
are supported by legs
110
and electrically connected to the semiconductor substrate
108
via the metal wiring film
104
contained in the legs
110
. As shown in FIG.
15
(
a
) and FIG.
16
(
a
), almost all of the surfaces of the diaphragm structural bodies
101
a
and
101
b
serve as first infrared radiation receiving areas (enclosed by broken lines).
In the thermal-type infrared radiation detector cells including arrangement (a) and (b), incident infrared rays shine down on the infrared radiation absorbing films
107
a
and
107
b
in the first infrared radiation receiving areas of the diaphragm structural bodies
101
a
and
101
b
respectively. Under these conditions, in technique (1), infrared rays are substa
Deguchi Haruhiko
Fukushima Toshihiko
Komoda Tomohisa
Birch Stewart Kolasch & Birch, LLP.
Hannaher Constantine
Lee Shun
Sharp Kabushiki Kaisha
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