Direct Write Technology of SIN Tunnel Junctions for Thermometry and Microwave Devices

Licentiatavhandling, 2008

This thesis concerns development of SIN junction technology for thermometry and microwave detectors, as well as technology of a planar phase switch as a part of integrated microwave receiver. Cold-Electron Bolometer (CEB) is a sensitive detector of a microwave radiation, in which SIN tunnel junctions are used for temperature measurement of a nanoscale absorber in the same way as in SIN thermometers. A novel direct-write trilayer technology and a Ti-based technology were developed for the CEB and thermometry. The trilayer technology is based on in-situ evaporation of the superconductive electrode followed by the oxidation and the normal counter-electrode as a first step and deposition of a normal-metal absorber as a second one. The junctions were characterized as temperature sensors, and a thermometer responsivity of 52 mV/K was observed for an array of 100 junctions in series with a temperature resolution of ± 5μK. A novel Ti-based direct-write technology for fabrication of Ti-TiO2-Al tunnel junctions has another advantages related to thickness of the absorber. In particular, a very thin and completely flat absorber can be created with no bending parts. The key point of this technology is deposition of Ti film as a base electrode and deposition of Al electrode after oxidation of Ti. The junctions are to be used for fabrication of microwave receivers for sensitive measurements in new generation of telescopes, e.g. CLOVER project including polarization Cosmic Microwave Background (CMB) radiation measurements, BOOMERANG and OLIMPO balloon telescope project which is dedicated to measuring the Sunyaev-Zeldovich effect in clusters of Galaxies. A planar phase switch operating at 97-225 GHz has been developed, fabricated, and tested. The system makes it possible to modulate the microwave signal or switch it between two branches of a circuit with low losses and high speed. The proposed fully planar design allows the switch to be integrated into the detector circuit. The phase modulation scheme will be used in high-precision astrophysical experiments such as the investigation of the polarization of the cosmic microwave background. Keywords: SIN tunnel junction, direct write technology, Cold-Electron Bolometer, cryogenic thermometry, phase switch, microwave device, noise equivalent power