Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2000-01-12
2002-12-17
Epps, Georgia (Department: 2873)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338100, C338S018000
Reexamination Certificate
active
06495829
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a thermal infrared array sensor for detecting a plurality of infrared wavelength bands.
FIG. 1A
is a schematic perspective view illustrative of a conventional thermistor bolometer thermal infrared array sensor.
FIG. 1B
is a fragmentary cross sectional elevation view illustrative of a conventional thermistor bolometer thermal infrared array sensor of FIG.
1
A. The conventional thermistor bolometer thermal infrared array sensor is disclosed by R. A. Wood, “Uncooled Infrared Image Arrays and Systems”, Semiconductors and Semimetals”, vol. 17, volume editors P. W. Kruse & D. D. Skatrud Academic Press, 1997, p. 103. The conventional thermistor bolometer thermal infrared array sensor is formed over a silicon substrate
308
. The conventional thermistor bolometer thermal infrared array sensor comprises a diaphragm
301
and beams
302
and a read out circuit
307
. The diaphragm
301
comprises a bolometer material thin film Vox
305
having a large temperature coefficient of zero-power resistance and protective films SiN
306
which sandwich and surround the bolometer material thin film Vox
305
. The beams
302
mechanically support the diaphragm
301
so that the diaphragm
301
is floated over the upper surface of the read out circuit
307
. The beams
302
are further provided with electric wirings which comprise metal thin films of NiCr having a low thermal conductivity, The read out circuit
307
is formed in an upper region of the silicon substrate
308
. A full reflective film
304
is provided over the read out circuit
307
. A cavity
309
is formed between the diaphragm
301
and the surface of the silicon substrate
308
. An infrared ray
300
is incident into the diaphragm
301
and a part of the incident infrared ray
300
is absorbed into the SiN protective films
306
whilst a remaining part of the incident infrared ray
300
is transmitted through the diaphragm
301
and the cavity
309
to the full reflective film
304
, whereby the remaining part of the incident infrared ray
300
is fully reflected by the full reflective film
304
and then absorbed into the SiN protective films
306
. The absorption of the infrared ray
300
causes a temperature rising of the diaphragm
301
. The temperature rising of the diaphragm
301
causes variation in a resistance of the bolometer whereby variation in voltage can be detected If a temperature of a sample is lower than the original temperature of the diaphragm
301
, then the diaphragm
301
shows a heat radiation to cause a temperature drop of the diaphragm
301
, whereby the resistance of the bolometer is varied. The infrared ray absorption band of the SiN protective films
306
is 10 micrometers wavelength band, for which reason the above thermal infrared sensor is operable in this wavelength band.
FIG. 2A
is a schematic perspective view illustrative of a conventional ferroelectric infrared array sensor.
FIG. 2B
is a fragmentary cross sectional elevation view illustrative of a conventional ferroelectric infrared array sensor of
FIG. 2A
The conventional ferroelectric infrared array sensor is disclosed by C. H. Hansen, SPIE Proc. 2020 vol. 1993, p. 330. The conventional ferroelectric infrared array sensor has a hybrid structure of ferroelectric ceramics
401
and a read out circuit
402
which are electrically connected via bumps
403
. An array of the ferroelectric ceramics
401
is provided on an infrared absorption layer
404
. Electrodes
408
are provided on the ferroelectric ceramics
401
. The electrodes
408
are electrically connected through the bumps
403
to the read out circuit
402
. The infrared absorption layer
404
comprises a cavity layer
406
having a first surface on which an infrared absorption film
405
is provided and a second surface opposite to the first surface, where on the second surface, a full reflective film
407
is provided. The ferroelectric ceramics
401
are provided on the full reflective film
407
. Each of the bumps
403
has an electric wiring
409
for electrically connect the electrode
408
to the read out circuit
402
. The conventional ferroelectric infrared array sensor is different in infrared absorption mechanism from the thermistor bolometer thermal infrared array sensor of FIG.
1
A. An infrared ray
400
is incident into the infrared absorption layer
404
. A part of the incident infrared ray
400
is reflected by the infrared absorption film
405
. A remaining part of the incident infrared ray
400
is transmitted through the cavity layer
406
to the full reflective film
407
. The remaining part of the infrared ray
400
is reflected by the full reflective film
407
and then transmitted through the cavity layer
406
to the infrared absorption film
405
The reflected infrared ray
400
is absorbed into the infrared absorption film
405
. The above two reflected infrared rays show interference to cancel to each other in the infrared absorption film
405
so that the infrared rays are absorbed into free electrons in the infrared absorption film
405
. The absorbed infrared rays are converted into a heat which causes a variation in dielectric constant of the ferroelectric ceramics
401
of (Ba, Sr)TiO
3
. The variation of the dielectric constant of the ferroelectric ceramics
401
causes a voltage variation. This infrared array sensor has a uniform thickness of the cavity layer, for which reason all pixels can detect the same wavelength band.
FIG. 3
is a schematic perspective view illustrative of a conventional dual band HgCdTe infrared array sensor which is different from the thermal infrared array sensors us shown in
FIGS. 1A and 2A
. The conventional dual band HgCdTe infrared array sensor has a hybrid structure of a silicon read out circuit and a two dimensional HgCdTe photo-diode array. The conventional dual band HgCdTe infrared array sensor is capable of detecting two different infrared wavelength bands concurrently in the same pixel. The conventional dual band HgCdTe infrared array sensor is thus of a dual band quantum infrared array sensor, In
FIG. 3
, the illustration of the silicon read out circuit is omitted. The conventional dual band HgCdTe infrared array sensor is disclosed in U.S. Pat. No. 5,149,956 issued to P. R. Norton. Each pixel
501
is formed on a CdZnTe substrate
502
which is transparent to infrared ray. The each pixel
501
comprises an n-Hg
0.7
Cd
0.3
Te layer
503
, a p-Hg
0.6
Cd
0.4
Te layer
504
, and an n-Hg
0,8
Cd
0.2
Te layer
505
. The n-Hg
0.7
Cd
0.3
Te layer
503
absorbs an infrared ray of a wavelength band of 3-5 micrometers. The n-Hg
0.7
Cd
0.3
Tc layer
503
has an energy band gap of about 0.24 eV and a thickness of 10 micrometers. The p-Hg
0.6
Cd
0.4
Te layer
504
has a larger energy band gap than the n-Hg
0.7
Cd
0.3
Te layer
503
. The n-Hg
0.8
Cd
0.2
Te layer
505
absorbs an infrared ray of a wavelength band of 10 micrometers. The n-Hg
0.8
Cd
0.2
Te layer
505
has an energy band gap of about 0.1 eV and a thickness of 10 micrometers. An In bump
506
is provided to mechanically and electrically connect the n-Hg
0.7
Cd
0.3
Te layer
503
to the read out circuit not illustrated. An In bump
507
is provided to mechanically and electrically connect the p-Hg
0.6
Cd
0.4
Te layer
504
to the read out circuit not illustrated. An In bump
508
is provided to mechanically and electrically connect the n-Hg
0.8
Cd
0.2
Te layer
505
to the read out circuit not illustrated. The p-Hg
0.6
Cd
0.4
Te layer
504
extends over the entire of the array to serve as a common electrode. The n-Hg
0.7
Cd
0.3
Te layer
503
and the n-Hg
0.8
Cd
0.2
Te layer
505
are independently provided for each pixel, so that each pixel has an independent npn stricture so that each pixel
501
can detect infrared rays of two different wavelengths.
First and second infrared rays
500
having short and long wavelengths are incident to the CdZnTe substrate
502
. The first infrared ray
500
having the short wavelength is absorbed into the n-Hg
0.7
Cd
0.3
Te layer
503
and the p-Hg
0,6
Cd
0.4
T
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