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Superconductivity in primary voltage metrology at INRiM
No full textPrimary electrical Metrology is among the first and, to date, one of the most active and successful research field for superconducting devices. Voltage standards based on the Josephson effect are in use since few years after it discovery and have enormously reduced the uncertainty of DC voltage calibrations. INRIM the Italian National Metrology Institute has a long tradition in research on the application of superconductivity to electrical standards. This paper is an overview of main results and ongoing activities
Temperature stability of SNIS Josephson arrays between 4.2 K and critical temperature in cryocooler
No full textCryogen-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
Realizzazione e caratterizzazione preliminare di un miscelatore SIS per applicazioni astrofisiche
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Superconducting and Dissipative Characteristics of Overdamped SNIS Josephson Junctions for Sensing Applications
Full text linkJosephson-junction devices such as suitably designed nanoSQUIDs can provide a sensing element for micro and nanoelectronics. In this paper, the properties of such device must be tailored in order to have an optimal response. In particular, it relates its temperature stability, and a comparatively weak dependence of the critical supercurrent Ic on temperature Tin the working range. To realize it, a concave upward Ic-versus-T curve is required. The aim of this paper was to study conditions when such temperature dependence can be realized in four-layered S/N-I-S Josephson junctions, mantaining the overdamped behavior. We show how the shape of the Ic-versus-T dependence can provide important information about the strength of the S/N proximity coupling
Cryogen-Free Operation of SNIS for AC Quantum Voltage Standards
Full text linkWe report on our recent and ongoing activities on helium-free operation with ac Josephson standards based on programmable superconductor-normal conductor-insulator-superconductor (SNIS) arrays. Liquid helium-free operation provides ease of use, which is a wider number of applications and users. Moreover, it allows to reduce cable loading, which is crucial to overcome frequency-related limitations to the accuracy. Thermalization problems not faced with helium cooling are still challenging, in particular with programmable standards. To identify the effect of He-free cooling on electrical behavior, we compared the array steps in cryocooler a liquid helium. Results show that SNIS arrays can be operated in cryocooler and are interesting for application to programmable voltage standard
On the synthesis of stepwise quantum waves using a SNIS programmable josephson array in a cryocooler
Full text linkThis paper presents recent advances in the application of binary-divided 1 V array, consisting of 8192 intrinsically shunted SNIS overdamped Josephson junctions (JJs), for the synthesis of stepwise waves with quantum accuracy. The maximum output voltage is ensured by opportunely driving the subsections of the SNIS array by means of three states bias-current setpoints to the Shapiro steps n = 0, +/- 1 or n = +/- 2, respectively. Reconfigurable digital modular electronics has been designed to bias individually each of the 13 subsections of the SNIS array. A two-stage closed cycle refrigerator equipped with LF and RF electrical lines is employed for cooling-down the SNIS array for temperatures ranging from 3.6 K to above 7 K. Stepwise sine waves with rms amplitude ranging from 1 to 2 V using the first (n = 1) and second (n= 2) Shapiro steps, different temperatures and bias-current setpoints have been synthesized up to the kHz range. The synthesized waves have been recorded and analyzed by a high-precision differential sampling system. We report the results of the first characterizations carried out with the new multibit current source and an improved version of the sample holder designed to optimize the heat dissipation of the SNIS array for operation in cryocooler setups
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