Ti-TiO2-Al normal metal-insulator-superconductor tunnel junctions fabricated in direct-write technology

We present a novel Ti- based direct- write technology for fabricating Ti - TiO2 - Al tunnel junctions for bolometer and thermometry applications. The goal of our research is to develop simple and efficient technology for fabricating SIS tunnel junctions between Ti and Al with TiO2 as an insulating barrier. The key point of this technology is the deposition of a Ti film as 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 the absorber with no limitation related to the area of the junctions or the thickness of the absorber. In particular, a very thin and completely flat absorber can be created with no bending parts, which is not possible using the shadow evaporation technique or standard trilayer technology. Besides, the proposed new approach does not require one- cycle evaporation for deposition of tunnel junctions which gives us more freedom in the geometry of the counter- electrodes. The junctions are to be used for bolometer applications, such as the fabrication of microwave receivers for sensitive measurements in new generation telescopes, e. g. CLOVER and BOOMERANG projects including polarization cosmic microwave background radiation measurements, and the OLIMPO balloon telescope project which is dedicated to measuring the Sunyaev - Zeldovich effect in clusters of galaxies. A s the first step, SIN tunnel junctions have been fabricated and characterized.