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

Abstract

Cryogen-free operation is essential to expand applications of superconductivity, is unavoidable in some special cases and, in perspective, provides a solution to the expected shortages of liquid helium. In electrical metrology applications, high-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 presently available. The superconductor-normal metal-insulator-superconductor (SNIS) technology developed at INRIM uses low-temperature superconductors but allows operation at temperatures close to 6 K. Thus, it is interesting for the cryocooler operation of a programmable voltage standard. We report on measurements of SNIS devices cooled with a closed-cycle refrigerator and in liquid helium to test the electrical behavior and its dependence on specific fabrication parameters that can be used to optimize the temperature stability

On the Synthesis of Stepwise Quantum Waves Using a SNIS Programmable Josephson Array in a Cryocooler

“…Ensuring stable operating margins of a programmable Josephson array in cryogen-free system as close as possible to those obtained in conventional liquid helium is a fundamental prerequisite. In particular, practical operations of cryogen-free programmable Josephson voltage standards fabricated with different technologies were demonstrated only at few National Metrology Institutes (NMIs) [9]- [12].…”

“…The experimental setup is an improved version of the one proposed for characterization of programmable Josephson voltage standards [12]. The main changes concern the upgrading of the modular electronics for separate biasing of subsections of the array, and the redesign of the sample holder for thermal anchoring of the SNIS array.…”

Thermal Performances of an Improved Package for Cryocooled Josephson Standards

“…The PJVS chip used in this experiment was fabricated in cooperation with PTB (Physikalisch-Technische Bundesanstalt) with the Superconductor-Normal-Insulator-Superconductor (SNIS) technology [16], developed for applications in quantum voltage metrology and with peculiar characteristic in terms of reduced temperature dependence of the electrical parameters [17]. Its operation was intensively investigated both in liquid helium and in cryocooler [18], [19].…”

Tests on waveform synthesis in a new cryocooler setup

“…This section summarizes the relevant properties of the cooling and measurement apparatuses. Detailed descriptions have been already published [3].…”