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arXiv:2403.08655 · Physical Review Applied

Efficient electronic cooling by niobium-based superconducting tunnel junctions

Joel Hätinen, Alberto Ronzani, R. P. Loreto, E. Mykkänen, A. Kemppinen, Klaara Viisanen, T. Rantanen, J. Geisor, J. S. Lehtinen, Mário Ribeiro, J.-P. Kaikkonen, O. Prakash, Visa Vesterinen, Christopher W. Förbom, E. T. Mannila, Mikael Kervinen, Joonas Govenius, Mika Prunnila

Published Dec 13, 2024• 7 citations
arXivHTMLPDF

Abstract

Replacing the bulky cryoliquid-based cooling stages of cryoenabled instruments by chip-scale refrigeration is envisioned to disruptively reduce the system size similar to microprocessors did for computers. Electronic refrigerators based on superconducting tunnel junctions have been anticipated to provide a solution, but reaching the necessary above the 1-K operation temperature range has remained a goal out of reach for several decades. We show efficient electronic refrigeration by $\mathrm{Al}$-${\mathrm{Al}\mathrm{O}}_{x}$-$\mathrm{Nb}$ superconducting tunnel junctions starting from bath temperatures above 2 K. The junctions can deliver electronic cooling power up to approximately $\mathrm{mW}/{\mathrm{mm}}^{2}$, which enables us to demonstrate tunnel-current-driven electron temperature reduction from 2.4 K to below 1.6 K (34% relative cooling) against the phonon bath. Our work shows that the key material of integrated superconducting circuits---niobium---enables powerful cryogenic refrigerator technology. This result is a prerequisite for practical cryogenic chip-scale refrigerators and, at the same time, it introduces a new electrothermal tool for quantum heat-transport experiments.

DOI
10.1103/physrevapplied.22.064048

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Replacing the bulky cryoliquid-based cooling stages of cryoenabled instruments by chip-scale refrigeration is envisioned to disruptively reduce the system size similar to microprocessors did for computers. Electronic refrigerators based on superconducting tunnel junctions have been anticipated to provide a solution, but reaching the necessary above the 1-K operation temperature range has remained a goal out of reach for several decades. We show efficient electronic refrigeration by Al\mathrm{Al}Al-AlOx{\mathrm{Al}\mathrm{O}}_{x}AlOx​-Nb\mathrm{Nb}Nb superconducting tunnel junctions starting from bath temperatures above 2 K. The junctions can deliver electronic cooling power up to approximately mW/mm2\mathrm{mW}/{\mathrm{mm}}^{2}mW/mm2, which enables us to demonstrate tunnel-current-driven electron temperature reduction from 2.4 K to below 1.6 K (34% relative cooling) against the phonon bath. Our work shows that the key material of integrated superconducting circuits---niobium---enables powerful cryogenic refrigerator technology. This result is a prerequisite for practical cryogenic chip-scale refrigerators and, at the same time, it introduces a new electrothermal tool for quantum heat-transport experiments.
Advancements in cryo-enabled fields like space electronics and quantum information increasingly demand efficient cooling of chips down to deep cryogenic temperatures. In this work, we present an overview of recent progress in chip-scale cooling technologies for cryogenic microsystems. We, especially, discuss the underlying operational principles and technological innovations of tunnel junction coolers and adiabatic field refrigeration methods, emphasizing their significance for on-chip cooling and scalable general purpose cooling platforms.
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We demonstrate highly transparent silicon–vanadium and silicon–aluminum tunnel junctions with relatively low sub-gap leakage current and discuss how a trade-off typically encountered between transparency and leakage affects their refrigeration performance. We theoretically investigate cascaded superconducting tunnel junction refrigerators with two or more refrigeration stages. In particular, we develop an approximate method that takes into account self-heating effects but still allows us to optimize the cascade a single stage at a time. We design a cascade consisting of energy-efficient refrigeration stages, which makes cooling of, e.g., quantum devices from above 1 K to below 100 mK a realistic experimental target.