Characteristics of Josephson Nb/Al/AlO$_{x}$/Nb Contacts Formed by Simplified Method

A. A. Kalenyuk$^{1,2}$, A. P. Shapovalov$^{1,2}$

$^{1}$Институт металлофизики им. Г. В. Курдюмова НАН Украины, бульв. Академика Вернадского, 36, 03142 Киев, Украина
$^{2}$Киевский академический университет НАН и МОН Украины, бульв. Академика Вернадского, 36, 03142 Киев, Украина

Получена: 17.02.2022; окончательный вариант - 11.08.2022. Скачать: PDF

The Josephson junctions are widely used as the main elements in various sensitive devices, such as SQUIDs, qubits, and digital superconducting appliances. Therefore, the development of technology for the large-scale fabrication of such junctions is an urgent problem of modern microelectronics. The main requirements for the technology are simplicity of its implementation, repeatability, and stability of transition characteristics. The paper presents two simplified CMOS-like technologies for manufacturing thin film niobium Josephson junctions with an aluminium oxide dielectric layer, which are implemented without the use of expensive precision etching systems. As shown, a high-quality Josephson junction can be formed even when the vacuum between deposition of the first niobium layer and the subsequent aluminium layer is violated. It was found that the use of an additional SiO$_{2}$ insulating layer with a window at the junction point excludes the direct current flow between the upper and lower niobium electrodes at the junction edges and thus allows completely exclude the laborious process of the edge anodizing. The revealed Shapiro steps on the current-voltage characteristics and suppression of the critical current by a small magnetic field of 7 mT parallel to the junction plane confirm the high quality of the fabricated Josephson junctions. The obtained temperature dependence of the superconducting gap is in a good agreement with the BCS model that indicates formation of the conventional $SIS$ type junction. Temperature dependences of the critical current and resistive transition of fabricated junctions are also obtained. From these dependencies, it follows that the critical temperatures of the upper and lower electrodes are unequal that can be explained by a significant difference in their thicknesses. From the carried-out measurements, the calculations of the McCumber–Stewart parameter, capacitance, normal resistance values, and also the dielectric layer thickness in the junction were performed. The developed technologies can be used for the large-scale production of $SIS$ Josephson junctions for applications in modern microelectronics.

Ключевые слова: Josephson junction, BCS theory, Shapiro steps, niobium, energy gap.


PACS: 73.50.-h, 74.25.fc, 74.25.Ha, 74.50.+r, 74.55.+v, 85.25.Cp

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