Method and apparatus for bias and readout of bolometers operated on a hysteretic metal-insulator transition
First Claim
1. A method for detecting a signal comprising:
- a) providing a bolometer comprising a material having an abrupt hysteretic change in electrical resistance responsive to temperature change;
said material being coupled to means for impinging said signal on said material;
b) applying an alternating current or chance in voltage across said material in an amount and for a period of time sufficient to cause a temperature change resulting in initiation of said abrupt change in resistance; and
c) detecting a resultant change in electrical resistance of said material for a selected optimal duration at a selected optimal time after applying said alternating current or voltage, said resultant change in electrical resistance being indicative of the presence and strength of said signal.
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Abstract
This invention consists of a bias and readout scheme for resistive bolometers. It is chiefly intended for use with bolometer materials which exhibit a phase transition that is hysteretic. A preferred bolometer material is vanadium dioxide, which has a metal-semiconductor phase transition at 68° C. and a hysteresis of typically 5° C., depending on material preparation. The existence of hysteresis precludes the use of a conventional dc bias or a conventional pulsed bias in a bolometer operated on the phase transition. In the present method, the bias consists of an ac current for phase transitions in which the resistance decreases with increasing temperature. For phase transitions in which the resistance increases with temperature, an ac voltage bias would be used.) The waveform of the ac bias consists of a short “reset” segment in which the peak current is high enough to bring the bolometer completely into its metallic state, followed by a longer “data” segment in which the bias current and bias power monotonically decrease, so as to sweep the bolometer'"'"'s physical temperature downward across the phase transition. The frequency of the ac bias is determined by the condition that the slew rate in bias power during the data segment must always exceed the slew rate in signal power, for all signals of interest. The signal is read out by averaging the bolometer voltage over a time window lying entirely within the data segment. With this bias and readout scheme, the full slope of the bolometer R(T) characteristic is reflected in the output from small signals, which would not be the case for a conventional dc or pulsed bias scheme. Since the full slope of the R(T) characteristic is accessible, the bolometer can operate in the extreme electrothermal feedback regime, which provides major improvements in speed, 1/f-noise, and sensitivity.
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Citations
20 Claims
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1. A method for detecting a signal comprising:
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a) providing a bolometer comprising a material having an abrupt hysteretic change in electrical resistance responsive to temperature change;
said material being coupled to means for impinging said signal on said material;
b) applying an alternating current or chance in voltage across said material in an amount and for a period of time sufficient to cause a temperature change resulting in initiation of said abrupt change in resistance; and
c) detecting a resultant change in electrical resistance of said material for a selected optimal duration at a selected optimal time after applying said alternating current or voltage, said resultant change in electrical resistance being indicative of the presence and strength of said signal.- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A bolometer for detecting a signal comprising:
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a) a material having an abrupt hysteretic change in electrical resistance responsive to temperature change;
b) means for applying an alternating current or change in voltage across said material in an amount and for a period of time sufficient to cause a temperature change resulting in initiation of said abrupt change in resistance;
c) means for detecting a resultant electrical resistance of said material for a selected optimal duration at a selected optimal time after applying said alternating current or voltage, said resultant electrical resistance being indicative of the presence and strength of said signal; and
d) a display for displaying detected resultant electrical resistance. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification