Fabrication of NIS and SIS Nanojunctions with Aluminum Electrodes and Studies of Magnetic Field Influence on IV Curves

Abstract

Samples of superconductor–insulator–superconductor (SIS) and normal metal–insulator–superconductor (NIS) junctions with superconducting aluminum of different thickness were fabricated and experimentally studied, starting from conventional shadow evaporation with a suspended resist bridge. We also developed alternative fabrication by magnetron sputtering with two-step direct e-beam patterning. We compared Al film grain size, surface roughness, resistivity deposited by thermal evaporation and magnetron sputtering. The best-quality NIS junctions with large superconducting electrodes approached a resistance R(0)/R(V2Δ) factor ratio of 1000 at 0.3 K and over 10,000 at 0.1 K. At 0.1 K, R(0) was determined completely by the Andreev current. The contribution of the single-electron current dominated at V > VΔ/2. The single-electron resistance extrapolated to V = 0 exceeded the resistance R(V2Δ) by 3 × 109. We measured the influence of the magnetic field on NIS junctions and described the mechanism of additional conductivity due to induced Abrikosov vortices. The modified shape of the SINIS bolometer IV curve was explained by Joule overheating via NIN (normal metal–insulator–normal metal) channels.

Superconducting thin films and tunnel junctions based on aluminum

“…Another important property of smooth barrier films is the high effective tunneling area. As we noted in [2], for rough films the area of the tunnel junction can be 10−20% of the sandwich area. If to divide the resistance quantum value by the junction resistance, one can obtain the number of parallel conduction channels.…”

“…For tunnel junctions, the height of the surface roughness profile from peak to trough (peak-to-peak) R pp , which varies from 2 to 10 nm for film thickness from 3 to 130 nm for thermal evaporation [1], is of importance. Magnetron sputtering makes it possible to obtain smoother films with R pp = 5 nm for a 150 nm film [2]. The conductivity and microwave properties depend on the lateral size of the crystallites, which are comparable to the film thickness during thermal deposition and up to 3 times larger in plan view during magnetron sputtering.…”

Electron-Phonon Interaction in Aluminum SINIS

“…At V/VΔ<0.3 obtained Te values slightly differ, which does not affect the results. But at low voltages there is a qualitative difference -the differential conductivity according to formula (4) changes linearly, which corresponds to experiment [17,18]. Equation ( 5) is similar to the calculation of Andreev current in [19].…”

Влияние гомобуферного слоя на морфологию, микроструктуру и твердость пленок Al/Si(111)

“…Так, при термическом напылении пленок алюминия толщиной до 20 nm величина RMS (root mean square) шероховатостей и максимальных отклонений поверхности (peak to peak) составляли 2.3 и 23.3 nm [12] соответственно. Переход на рост пленок методом магнетронного распыления позволил получить на пленках алюминия толщиной 150 nm более гладкие поверхности с rms ∼ 5 nm [14]. Проблема шероховатости поверхности пленок тесно связана с термодинамическими условиями их роста.…”