Evaluation of high-frequency performances of a superconducting base transistor using high-Tc materials

The high-frequency performances-cutoff frequency f_T , maximum oscillation frequency f_max, and so on-for a superconducting base transistor using high-T_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_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 Δ(T) of the base superconductor, (3) Critical temperature T_c=90 K, superconductor energy gap at zero kelvin Δ(0)=30 meV, carrier concentration n=10²¹ cm^-3, resistivity ρ=100 μΩcm, magnetic penetration depth λ=0.1 μm, and effective mass m=5 m₀ in the emitter and base superconductors. Calculated results reveal that high-T_c superconducting base transistors have a potential for much higher high-frequency performance values than conventional devices. For example, typical f_T, f_max, and switching energy values are estimated to be 1 THz, 1 THz, and 10^-20 J/gate, respectively