Josephson junction based thermometer and its application in bolometry

We propose a new type of a transition edge sensor based on an Al/AlOx/Ti/AlOx/Al superconductor - insulator - superconductor - insulator - superconductor (SIS'IS) structure. It exhibits sharp dependence of zero bias resistance on temperature of the titanium absorber in the vicinity of its superconducting critical temperature. We demonstrate temperature sensitivity of the device to be $2\ μ\text{K}/\sqrt{\text{Hz}}$. Noise Equivalent Power (NEP) of the device, limited by the amplifier noise, is estimated to be $4\times 10^{-17}\ {\rm W}/ \sqrt{\rm Hz}$ at 313 mK. The tunnel junctions between superconducting leads should help to overcome the size limitation imposed by proximity effect in conventional transition edge sensors, without sacrificing the sensitivity. Besides that, the input resistance of the device can be tuned in a wide range.

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