Infrared Detector Arrays

23 .32 IMAGING DETECTORS
TABLE 2 State-of-the-Art Staring PtSi FPAs
Type of FPA
Pixel
size
( m 2 )
Fill
factor
Design
rules
( m)
Q m a x
10 6
(e - / p)
NE T
(K) f / 4 Year Company
References
320 244 IT-CCD
680 480 MOS
40 40
24 24
44
38
2 . 0
1 . 5
1 . 4
1 . 5
0 . 04
0 . 06
1 . 4
1 . 0
1988
1991
Sarnof f 52
53
324 487 IT-CCD
648 487 IT-CCD
42 21
21 21
42
40
1 . 5
1 . 3
0 . 25
1 . 5
0 . 10
0 . 10
1 . 0
1 . 0
1988
1991
NEC 54
55
256 244 IT-CCD 31 . 5 25 36 1 . 8 0 . 55 0 . 07 1 . 8 1989 Loral 56
512 512 IT-CCD
Fairchild
640 486 IT-CCD
noninterl . 4-port
25 25 54 1 . 2
0 . 23 0 . 15 2 . 8 1990
Kodak
57
interlaced 1-port
0 . 55 0 . 1 2 . 8 1991
512 512 CSD 26 20 39
71
2 . 0
1 . 2
0 . 7
2 . 9
0 . 1
0 . 033
1 . 5
1 . 5
1987
1992
Mitsubishi 58
59
1040 1040 CSD 17 17 53 1 . 5 1 . 6 0 . 1 1 . 2 1991 45
4-port
400 244 hybrid
640 488 hybrid
4-point
24 24
20 20
84
80
2 . 0
2 . 0
0 . 75
0 . 75
0 . 08
0 . 1
1 . 8
2 . 0
1990
1991
Hughes 60
61
most mature FPA technology for SWIR and MWIR applications that are compatible with
relatively low quantum ef ficiency of PtSi SBDs . Since these FPAs are fabricated by a
well-established silicon VLSI process , they can be fabricated with very good response
uniformity and high resolution .
A scanning PtSi FPA with 4 banks of 4096-element bilinear CCD line sensors was
developed by Mitsubishi and the 2048 16 TDI-elements FPAs were reported by Kodak
and Itek 5 1 for space-born remote sensing applications .
Table 2 summarizes the characteristics of recently developed monolithic and hybrid PtSi
FPAs with IR-CCD , CSD , and MOS silicon multiplexers . In addition to the pixel size and
fill factor , this table also shows the process design rules , maximum charge signal , Q m a x , the
reported noise equivalent temperature (NE T) for operation with specific f / 4 optics , the
associated company , and the pertinent references .
The largest resolution was demonstrated with 1040 1040 CSD , and the largest fill
factor for a monolithic 512 512 CSD FPA is 71 percent . This should be compared with a
fill factor of 80 percent for a 640 480 hybrid FPA . Thermal imaging demonstrated with
Sarnof f 640 480 PtSi low-noise MOS FPA is shown in Fig . 15 .
While PtSi SBDs operating at about 77 K are useful for SWIR and MWIR applications ,
LWIR response can be obtained with IrSi SBDs that require operation at about 40 K for
low dark current .
High quantum ef ficiency FPAs proliferate the 256 256 format since this is the
minimum format needed for imagers with near-TV resolution . About a half-dozen vendors
of fer DI-based FPAs , but there is variability in sensor sensitivity . The best devices have
yielded field-tested camera NE T’s approaching 10 mK . PACE-I 256 256 FPAs , for
example , of fer this sensitivity at temperatures above 100 K with residual nonuniformity of
0 . 012 percent after correction , which is the lowest yet reported by any FPA technology .
The residual nonuniformity is nearly a factor of 10 better than that previously considered
by spatial noise analysts . InSb-based imagers should perform similarly at lower temperatures
, but the data is apparently unavailable at this time .
Whereas improved materials technology has already resulted in increased pixel count
for unprecedented sensitivity at TV-type spatial resolution , HgCdTe advocates are also