Tests of SNIS Josephson Arrays Cryocooler Operation

Abstract

Cryogen-free operation of is essential to spread applications of superconductivity and is indeed unavoidable in some cases. In electrical metrology applications, higher temperature operation to reduce the refrigerator size and complexity is not yet possible, since arrays of Josephson junctions for voltage standard applications made with high-temperature superconductors are not yet available. The superconductor-normal metal-insulator-superconductor (SNIS) technology developed at INRIM uses low temperature superconductors, but allows operation well above liquid helium temperature. It is thus interesting for application to a compact cryocooled standard. We studied SNIS devices cooled with a closed-cycle refrigerator, both in DC and under RF irradiation. Issues related to thermal design of the apparatus are analyzed. The dependence of RF steps on the number of junctions observed is discussed in detail and interpreted as a consequence of power dissipated inside the chip

Temperature Stability of SNIS Josephson Arrays Between 4.2 K and Critical Temperature in Cryocooler

“…When comparing helium gas with cryocooler data [17], one can see that the step is reduced in the latter case from approximately 0.5 mA to about 0.2 mA. In the inset a higher resolution plot of the step profile is shown for a lower order Fig.…”

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

“…The Si diodes temperature was read with a cryogenic controller, a Lake Shore 350 (LS350, henceforth). Both Cu carrier and coldplate are thermally and electromagnetically shielded in the setup realized for high accuracy measurements for metrology [16]. A manganin wire of resistance R h ≃ 80 Ω at 4.2 K is wound around the coldplate disk as heater, when the temperature is closed-loop controlled.…”

Characterization of a Josephson array for pulse-driven voltage standard in a cryocooler

“…The cold finger top was fitted with an additional disk retaining inside a deep-set thermometer that, along with a heater wire wound around it, allows fine temperature monitoring and control. A second thermometer close to the chip was used to better estimate the array operating conditions and detect unwanted thermal gradients [15].…”