Ti–TiO2–Al normal metal–insulator–superconductor tunnel junctions fabricated in direct-writetechnology

Abstract

We present a novel Ti-based direct-write technology for fabricatingTi–TiO2–Al tunnel junctions for bolometer and thermometry applications. The goal of our research is todevelop simple and efficient technology for fabricating SIS tunnel junctions between Ti and Al withTiO2 as an insulating barrier. The key point of this technology is the deposition of a Ti filmas a base electrode and deposition of an Al electrode after oxidation of the Ti.This approach allows one to realize any geometry of the tunnel junctions and of theabsorber with no limitation related to the area of the junctions or the thickness of theabsorber. In particular, a very thin and completely flat absorber can be created with nobending parts, which is not possible using the shadow evaporation technique or standardtrilayer technology. Besides, the proposed new approach does not require one-cycleevaporation for deposition of tunnel junctions which gives us more freedom in the geometryof the counter-electrodes.The junctions are to be used for bolometer applications, such as the fabrication ofmicrowave receivers for sensitive measurements in new generation telescopes,e.g. CLOVER and BOOMERANG projects including polarization cosmic microwavebackground radiation measurements, and the OLIMPO balloon telescope project whichis dedicated to measuring the Sunyaev–Zeldovich effect in clusters of galaxies.As the first step, SIN tunnel junctions have been fabricated and characterized.