Direct-write trilayer technology for Al–Al2O3–Cu superconductor-insulator-normal metal tunnel junction fabrication

Abstract

The authors present a novel direct-write trilayer technology for bolometer and thermometry applications. The technology is based on in situ evaporation of the superconductive electrode followed by the oxidation and the normal counterelectrode as a first step and deposition of normal-metal absorber as a second one. This approach allows one to realize any geometry of the tunnel junctions and of the absorber with no limitation related to the size of the junctions or the absorber, which is not possible using shadow evaporation technique. The proposed new approach is perfectly suited for fabrication of microwave receivers for high-precision measurements in new generation of telescopes such as CLOVER ground-based telescope and OLIMPO balloon telescope projects. Measurements performed at 300mK showed high quality of fabricated tunnel junctions, low leakage currents, and Rd∕Rn ratio of 500 has been achieved at that temperature. The junctions were characterized as temperature sensors, and voltage versus temperature dependence measurements have shown a dV∕dT of 0.5mV∕K for each single junction, which is typical for this kind of tunnel junctions.