Millimetre wavelength detection using Nb/NbOx/Pb alloy tunnel junctions

Quasiparticle mixers have shown promise as millimetre and submillimetre wavelength detectors and mixers, with the potential for conversion gain and photon noise limited performance. We report on small area (0.1μm²- 1.0μm²) superconducting thin film edge junctions fabricated using a combination of magnetron sputter deposition and broad beam ion source technology for materials deposition, barrier formation, and electrode patterning. Devices fabricated on mm³quartz substrates with a wide range of normal state resistances, and critical current densities, Acm^-2, show steps due to photon assisted tunnelling with very small amounts of local oscillator power applied (10^-8W). We have investigated a series of devices with various electrical characteristics and geometries all of which include integral superconducting choke structures. Results are presented and are compared with theoretical predictions.