The energy distribution and emission efficiency of electrons emitted from a superconductor-insulator-superconductor (SIS) junction have been investigated by numerical calculation adopting the free electron model. The emission efficiency of an SIS junction cold cathode was found to be about 0.3% of tunneling current flowing to the SIS junction when the energy gap voltage of superconductor was 20 meV, the work function of counter electrode 1 eV, the bias voltage 0.96 V, the thickness of the counter electrode 100 , the electric field strength between the plate and the counter electrode 106 V/m, and the relaxation time 0.01 ps. It is clear that the SIS junction cold cathode can emit electrons with sharper energy distributions at much the same efficiency as compared with a metal-insulator-metal (MIM) junction cold cathode.

A 270 GHz-band image rejection SIS mixer is developed. This mixer employs planer type image rejection configuration and is integrated into a single-chip as in MMIC's at microwave frequency. In order to use sapphire substrate at 270 GHz-band, CPW transmission lines are selected to realize 50-70Ω characteristic impedances. The fabricated MMIC SIS mixer performs 12-24 dB image rejection ratio with 450-780 K noise temperature at 270 GHz.

A 90 GHz band planar-type superconducting mixer using Ba1-xKxBiO3 (BKBO) bicrystal junctions was fabricated on a MgO bicrystal substrate. The mixer is integrated with microwave circuits and two junctions, but we could not operate the mixer in image rejection mode because of process damage to the junction properties. However we confirmed the mixing operation; the intermediate frequency (IF) signal was observed up to 17K (LO87 GHz, RF92 GHz).