Evaluation of high-frequency performances of a superconducting base transistor using high-T/sub c/ materials

The high-frequency performances-cutoff frequency f/sub T/, maximum oscillation frequency f/sub max/, and so on-for a superconducting base transistor using high-T/sub c/ materials are evaluated. Calculations are based on a number of key assumptions, summarized as follows: (1) The quasiparticle density of state in high-T/sub c/ oxide superconductors and tunneling between the emitter and base superconductors can be expressed in terms of conventional theories, (2) The barrier height of the Schottky junction between the base superconductor and the collector semiconductor is equal to the gap energy Delta (T) of the base superconductor, (3) Critical temperature T/sub c/=90 K, superconductor energy gap at zero kelvin Delta (0)=30 meV, carrier concentration n=10/sup 21/ cm/sup -3/, resistivity rho =100 mu Omega cm, magnetic penetration depth lambda =0.1 mu m, and effective mass m=5 m/sub 0/ in the emitter and base superconductors. Calculated results reveal that high-T/sub c/ superconducting base transistors have a potential for much higher high-frequency performance values than conventional devices. For example, typical f/sub T/, f/sub max/, and switching energy values are estimated to be 1 THz, 1 THz, and 10/sup -20/ J/gate, respectively.