Thermal type infrared ray detector with thermal separation...

Details Thermal type infrared ray detector with thermal separation... Thermal type infrared ray detector with thermal separation...

2000-07-24

2002-08-27

Epps, Georgia (Department: 2873)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S338200, C250S338300, C250S338400

Reexamination Certificate

active

06441374

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thermal type infrared ray detector with a thermal separation structure.
2. Description of the Related Art
As an infrared ray detecting device, a detecting device of a thermal separation structure is known as “Monolithic Silicon Micro-bolometer Arrays” in “Uncooled Infrared Imaging Arrays and Systems” by R. A. Wood, (Semiconductors and Semimetals, Volume 47, volume editors P. W. Kruse and D. D. Skatrud, Academic Press, 1997, p103).
FIGS. 1 and 2
show such a thermal separation structure of a picture element of a bolometer type uncooled infrared sensor array. As shown in
FIGS. 1 and 2
, a readout circuit
102
for bolometer is formed in a Si substrate
101
, and a diaphragm
105
is supported by two beams
104
to form an air gap
103
between a semiconductor
101
and the diaphragm
105
. The structure material of the beam
104
is a protective insulating film
106
of silicon nitride and the thickness of a wiring line film which is formed of NiCr on the beam
104
is 50 nm. The diaphragm
105
as a light receiving section is composed of a thin film
107
of vanadium oxide with the resistance of 20 k&OHgr; as a bolometer material and a protective insulating film
106
of silicon nitride with the thickness of 800 nm. A full reflection film
108
is formed on the surface of the readout circuit
102
through the protective insulating film.
When infrared rays
109
are incident on the diaphragm
105
in such a thermal separation structure, the infrared rays
109
are absorbed by the silicon nitride thin film
106
. A part of the infrared rays
109
passes through the diaphragm
105
and then is reflected to the direction of the diaphragm
105
by the reflection film
108
. Thus, the reflected infrared rays are absorbed once again by the silicon nitride thin film
106
. In this way, the infrared rays are absorbed so that the temperature of the diaphragm
105
changes. The resistance of the bolometer thin film
107
changes through the change of the temperature, and is converted into a voltage change by the readout circuit. Thus, an infrared picture is obtained.
Also, as the infrared ray detecting device, a bolometer type noncooled infrared sensor array by H. Wada et al., (SPIE Vol. 3224, 1997, p40) is known.
FIGS. 7 and 8
show a thermal separation structure of a picture element of the bolometer type noncooled infrared sensor array.
FIG. 3
is a plan view showing the picture element, and
FIG. 4
is a sectional view of the picture element along a broken line shown by a point line of A
1
-A
2
-A
3
-A
4
-A
5
-A
6
-A
7
-A
8
-A
9
-A
10
. A diaphragm
113
is supported by two beams
112
to form an air gap between the diaphragm
113
and a silicon substrate
111
with a readout circuit. The structure material of the beam
112
is a protective insulating film
114
of silicon nitride, and a wiring line material
115
of the beam
112
is a Ti film having the thickness of 100 nm. The diaphragm
113
as a light receiving section is formed of a vanadium oxide thin film
116
with the sheet resistance of 10 to 30 k&OHgr;/sq as bolometer material, an protective insulating film
117
of silicon nitride with the thickness of 400 nm and an infrared absorption film
118
of TiN thin film with the thickness of 15 nm.
The wiring line
115
on the beam
112
is connected with the readout circuit in the silicon substrate
111
by wiring line plugs
121
through a contact
120
provided in a bank section
119
. Also, a reflection film
122
of a WSi film with the thickness of 20 nm and a protective insulating film
123
are formed on the silicon substrate through a thermal oxidation film.
The distance between the reflection film
122
and the infrared absorption film
118
is adjusted to 1/(4n) of the wavelength of an infrared ray to be detected (n is effective refractive index). The infrared rays are absorbed by the infrared absorption film
118
. A part of the infrared rays passes through the infrared absorption film
118
, and then are reflected by the reflection film
122
to the direction of the diaphragm
113
. In the diaphragm
113
, the infrared rays interfere with each other so that a component of the infrared rays with the wavelength to be detected is absorbed by the infrared absorption film
118
. Thus, change of the temperature of the diaphragm is caused. The resistance of the bolometer thin film
116
changes through the change of the temperature, and the change of the resistance is converted into a voltage change by the readout circuit. In this way, an infrared picture is obtained.
Also, as the infrared ray detecting device, a micro-bolometer array by Cunningham et al., (U.S. Pat. No. 5,688,699) is known.
FIG. 5
shows a thermal separation structure of a picture element of the micro-bolometer array. As shown in
FIG. 5
, an epitaxial layer
131
is grown on a silicon substrate
130
, and a readout circuit for the bolometer is formed in the epitaxial layer
131
. A diaphragm
133
is provided above the epitaxial layer
131
and is supported by two beams
132
and
132
′ to form an air gap between the diaphragm
133
and the epitaxial layer
131
.
The structure material of the beam
132
or
132
′ is silicon nitride
134
, and a wiring line
135
on the beam
132
or
132
′ is formed of a Cr film with the thickness of 10 nm and a Ni film with the thickness of 20 nm. The diaphragm
133
as a light receiving section is formed of a vanadium oxide thin film
136
of bolometer material with the sheet resistance of 15 to 30 k&OHgr;. Also, the diaphragm
133
is further composed of a protective insulating film
137
of silicon nitride with the thickness of 100 nm and an infrared absorption film of a gold thin film having the thickness of 10 nm. In
FIG. 5
, the absorption film is not shown.
The diaphragm
133
and wiring line films are electrically connected by contact sections
138
a
and
138
b
formed of the bolometer material. Also, the wiring line films and the readout circuit in the epitaxial layer are electrically connected by a contact
139
. Also, the epitaxial layer
131
is covered by a SiO
2
protective insulating film
140
and a reflection film composed of a Pt film with the thickness of 50 nm and a Cr film with the thickness of 5 nm. In
FIG. 5
, a reflection film is not shown.
The distance between the reflection film and the infrared absorption film is adjusted to ¼n of a detection wavelength (n: effective refractive index). The infrared rays absorbed by the infrared absorption film and the infrared rays passing through the infrared absorption film and then reflected by the reflection film to the direction of the diaphragm interfere with each other. As a result, the infrared rays with the detection wavelength are absorbed by the infrared absorption film, so that the temperature of the diaphragm changes. The resistance of the bolometer thin film changes through the change of the temperature, and the change of the resistance is converted into a voltage change by the readout circuit. In this way, an infrared picture is obtained.
Also, as the infrared ray detecting device, a pyroelectric-type array by Hanson et al., (SPIE vol. 3379, 1998, p60) is known.
FIGS. 6 and 7
are a thermal separation structure of a picture element of the pyroelectric type array. As shown in
FIGS. 6 and 7
, a diaphragm
152
is supported by two beams
151
to form an air gap′ between the diaphragm
152
and a silicon substrate
150
with a readout circuit. The diaphragm
152
is composed of a lower electrode
153
of Pt/Ti, a pyroelectric thin film
154
of (Pb,La)(Zr,Ti)O
3
with the thickness of 250 to 350 nm on the electrode
153
and an upper electrode
155
of a Nickel-Chrome thin film. One of the two beams
151
is composed of the lower electrode
153
and the pyroelectric thin film
154
, and the other beam
151
is composed of the pyroelectric thin film
154
and the upper electrode
155
. The thermal conduction of such a well known thermal separation structure of is determined b

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