Complex cryogenics still represents a strong limitation to the spread of Josephson voltage standards, and cryogenfree cooling is particularly suitable to simplify their operation. The main downsides of liquid-helium-free systems are related to the chip thermalization: Indeed, at low temperature, the heat transfer between the chip and the coldplate of a cryocooler in vacuum is strongly affected by the quality of the interfaces. In order to increase the thermal performances of cryocooled programmable Josephson standards, we devised and tested a special cryopackage: The chip is embedded into a sandwich structure with high-thermal-conductivity materials subject to a controlled mechanical pressure to reduce the thermal contact resistances. A thin sapphire lamina placed upon the chip allows the heat to be dissipated from the top, thus creating an additional path for the thermal flow. A special bridgelike system with a screw is used as a reproducible torque-to-force converter to exert known pressures to the sandwich. Furthermore, we analyzed the effect of thermal contraction to the actual pressure exerted on the chip, showing a nonnegligible increase when cooled down to cryogenic temperature that can be calculated and corrected for.

Thermal Performances of an Improved Package for Cryocooled Josephson Standards / Durandetto, Paolo; Monticone, Eugenio; Serazio, Danilo; Sosso, Andrea. - In: IEEE TRANSACTIONS ON COMPONENTS, PACKAGING, AND MANUFACTURING TECHNOLOGY. - ISSN 2156-3950. - 9:7(2019), pp. 1264-1270. [10.1109/TCPMT.2019.2901297]

Thermal Performances of an Improved Package for Cryocooled Josephson Standards

Durandetto, Paolo
;
Monticone, Eugenio;Serazio, Danilo;Sosso, Andrea
2019

Abstract

Complex cryogenics still represents a strong limitation to the spread of Josephson voltage standards, and cryogenfree cooling is particularly suitable to simplify their operation. The main downsides of liquid-helium-free systems are related to the chip thermalization: Indeed, at low temperature, the heat transfer between the chip and the coldplate of a cryocooler in vacuum is strongly affected by the quality of the interfaces. In order to increase the thermal performances of cryocooled programmable Josephson standards, we devised and tested a special cryopackage: The chip is embedded into a sandwich structure with high-thermal-conductivity materials subject to a controlled mechanical pressure to reduce the thermal contact resistances. A thin sapphire lamina placed upon the chip allows the heat to be dissipated from the top, thus creating an additional path for the thermal flow. A special bridgelike system with a screw is used as a reproducible torque-to-force converter to exert known pressures to the sandwich. Furthermore, we analyzed the effect of thermal contraction to the actual pressure exerted on the chip, showing a nonnegligible increase when cooled down to cryogenic temperature that can be calculated and corrected for.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11696/65635
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