Using a Josephson junction as an effective on-chip temperature sensor

Abstract

Temperature sensing and control are essential in experiments running in cryocooled systems, as with the case of liquid helium-free superconducting devices. A Josephson junction as on-chip temperature sensor operated in ac provides the highest sensitivity and minimal power loading to the cryogenic environment, thanks to the noise rejection of lock-in detection. To demonstrate the advantages of on-chip sensing, we tested it with a Josephson voltage standard array in cryocooler and compared with the conventional case of a sensor on the cold surface of the refrigerator, showing that the power dissipated within the chip may further increment the device temperature up to some tenths of kelvin. An ac Josephson junction sensor is proven to be capable of directly stabilizing the temperature of the superconductive circuit from fluctuations of dissipated power during operation. Reliability issues related to flux trapping are discussed and solutions are proposed suited to different applications. Overall, on-chip control with ac Josephson temperature sensing has the advantage of avoiding the complexities in minimization of cryogenic thermal links, virtually reducing to zero the contact resistance and keeping the operating temperature of the superconductor constant, independently of instantaneous operating power.

Verification of thermal converters by means of a pulsed Josephson standard

“…In addition, one of the two available JAWS array was investigated as on-chip temperature sensor, in a similar way as described in Ref. [13]. This would ensure the stabilization of the actual chip temperature even when microwave pulses are applied to the junctions, which is particularly critical at lower temperatures, owing to the reduced thermal conduction.…”

Recent advancements and perspectives of INRiM’s time-dependent Josephson voltage standards

“…More recent studies have shown that thermal issues in cryocooler operation of quantum standards can be tackled directly by a refined control of the average temperature of the chip [40]: the latter can be monitored and stabilized using Josephson junctions as thermal sensor, thanks to the strong dependence of electrical parameters with temperature in the superconducting state. Also, on-chip active compensation of temperature fluctuations, caused by the cooling cycle exploited by the cryocooler, is underway to cancel the annoying effect of Josephson junction IV curves "breathing" in phase with the cryocooler motion, causing the current-amplitude of quantum voltages steps to be largely reduced and, in the worst case, completely unusable.…”

Advancements in quantum voltage standards for time-dependent signals

“…Proper operation of a Josephson standard in cryocooler is always a challenging task, owing to the tight thermalization requirements [30,31] alongside the need of supplying non negligible dc and rf power for proper operation. We addressed the issue of designing an optimized cryopackage for maximizing the thermal contact between the chip and the cooling surface [32].…”