Dual spiral photoconductive detector

Details Dual spiral photoconductive detector Dual spiral photoconductive detector

1984-08-31

2001-01-30

Buczinski, Stephen C. (Department: 3662)

Radiant energy

Invisible radiant energy responsive electric signalling

Semiconductor system

C244S003160, C250S203100, C250S203600, C250S342000, C250S234000

Reexamination Certificate

active

06180945

ABSTRACT:

TECHNICAL FIELD
This invention pertains to the field of radiation detectors in which the resistance therethrough changes in response to the amount of incident radiation impinging thereon.
BACKGROUND ART
U.S. Pat. No. 3,745,360 describes a radiation detector that, like the present invention, has a circle-shaped outer contour. However, the reference differs from the present invention in that: 1) four radiation-sensitive resistances are arranged in a bridge circuit, rather than a single continuous photoconductor being used; 2) the radiation-sensitive resistances do not have a dual interleaved spiral configuration; 3) the reference is a staring type of detector, rather than one which is circularly scanned; and 4) it would be hard to use this technique with the preferred HgCdTe of the present invention because HgCdTe has too low a resistance.
U.S. Pat. No. 3,995,159 discloses a rectangular HgCdTe photoconductive element that is designed to be part of a larger array. It does not have a dual spiral pattern. It is used with a linear raster scan, rather than with a circular scan.
U.S. Pat. No. 4,024,397 is an infrared thermistor bolometer detector that senses temperature differentials by means of changes in resistance. Current and voltage differentials are measured, as in the present invention. However, the one or two bolometer flakes 28, 29 are not configured in a dual spiral pattern.
U.S. Pat. No. 4,027,160 discloses an array of detectors of rectangular size, using various reticle patterns, including zig zag ones. It does not disclose a detector having a dual spiral pattern.
U.S. Pat. No. 2,999,177 discloses a lead sulfide vidicom, i.e., a mosaic array of many rectangular monolithic lead sulfide detectors. Information is stored in the array, then interrogated by an electron beam.
U.S. Pat. No. 3,426,198 discloses an array of square monolithic lead sulfide detectors.
U.S. Pat. No. 3,727,057 discloses an array of rectangular photoconductive detectors having oppositely poled adjacent elements.
DISCLOSURE OF INVENTION
The present invention is a substantially planar photoconductive detector (
3
) having an outer contour substantially in the shape of a circle (
10
) and comprising a single continuous photoconductive strip (
1
,
2
). The strip comprises two interleaved photoconductive paths (
1
,
2
) each in the shape of a spiral. The paths (
1
,
2
). are connected together at a point (
19
) that defines the central point of each of the spirals.
Two gaps (
5
,
6
) that are narrow compared with each of the photoconductive paths (
1
,
2
) separate the paths (
1
,
2
).
A preferred material for the photoconductor (
3
) is mercury cadmium telluride (HgCdTe). This material has a low resistivity, and therefore the dual spiral configuration advantageously increases the resistance for a given area of photoconductor (
3
) by means of lengthening the paths (
1
,
2
). When used as an infrared detector (
3
) on board a missile (
17
), the detector (
3
) is preferably used with a circular scan projector (
14
) which, e.g., converts a remote point target (
13
) into a circle (
4
) on the surface of the detector (
3
).
Advantages of the present detector (
3
) over the prior art include:
1. Since the detector (
3
) active area is substantially circular (
10
), there is better matching to the circular optics (
14
) used in many missiles (
17
). Compared with a square or rectangular detector (
8
), unused corners (
23
), which only add to the noise without contributing to the detecting capability, are avoided.
2. The photoconductive paths (
1
,
2
) contain no sharp bends. Bends contribute to higher noise, decreasing the figure of merit D* of a detector, because they create differential current densities, producing changes in noise and in sensitivity.
3. The gaps (
5
,
6
) between the paths (
1
,
2
) are well suited to a rotating scanning optical system (
14
), thereby increasing the performance of the detector (
3
), because as the target (
13
) is replicated as a scanning circular band (
4
) across the surface of the detector (
3
), the gaps (
5
,
6
) are nearly parallel to the scan direction of the circular band (
4
). If the band (
4
were to encounter perpendicular or nearly perpendicular gaps (
5
,
6
), unwanted modulations would be much more severe.
4. The paths (
1
,
2
) have substantially uniform width, further avoiding unwanted modulations of the detected signals.


REFERENCES:
patent: 2668184 (1954-02-01), Taylor et al.
patent: 2999177 (1961-09-01), Null et al.
patent: 3296443 (1967-01-01), Argyle
patent: 3426198 (1969-02-01), Autrey
patent: 3494576 (1970-02-01), Lamelot
patent: 3727057 (1973-04-01), Higby et al.
patent: 3745360 (1973-07-01), Paul
patent: 3995159 (1976-11-01), Elliott
patent: 4024397 (1977-05-01), Weiner
patent: 4027160 (1977-05-01), Driffield et al.
patent: 4040744 (1977-08-01), Schertz et al.
patent: 4244540 (1981-01-01), Vollmerhausen
patent: 4383663 (1983-05-01), Nichols

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