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Josephson Junction Bolometer

IP.com Disclosure Number: IPCOM000087189D
Original Publication Date: 1976-Dec-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Broom, RF: AUTHOR

Abstract

As an alternative to known bolometers based on the superconducting-normal transition of a thin film, a bolometer may be based on a Josephson junction.

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Josephson Junction Bolometer

As an alternative to known bolometers based on the superconducting-normal transition of a thin film, a bolometer may be based on a Josephson junction.

If a tunnel junction is formed between two dissimilar superconductors having different critical temperatures T(c1) and T(c2), the Josephson current dependence upon T approaches an infinite slope as T(c2), the lower of the two T(c)'s, is approached from below (Fig. 1). Examples of possible electrode pairs are Al-Sn, Sn-Pb and Pb-Nb. At a temperature slightly below T(c1), the I-V characteristic of such junctions is as sketched in Fig. 2.

To measure the output signal, the device JJ may be connected to an AC current source and a resonant circuit, as shown in Fig. 3. The characteristics of the resulting signal S(R) for different drive currents i(d) are shown in Fig. 4.

In comparison with the transition-edge bolometer, there is no phase change associated with the Josephson junction bolometer. Therefore, it is potentially faster. Second, the resistance in the voltage state is constant and may be made relatively high (ca. 10 ohms), facilitating matching to the amplifier. Higher impedances can be obtained by the series connection of an array of junctions.

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