The Josephson triode is a superconducting three terminal device and is used as a heterodyne mixer which has the internal frequency-variable local oscillator. We have fabricated the Josephson triode by integrating the planar-type Josephson junctions and investigated their current-voltage characteristics.

The Finite-Difference Time-Domain (FDTD) method has been applied to study the scattering characteristics of Fabry-Perot cavities with infinite planar periodic surfaces. Periodic Boundary Conditions (PBC) are used to reduce the analysis to one unit periodic volume. Both dielectric and metallic losses are included in the algorithm using a frequency dependent formalism. This technique is used to study the frequency response of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. These cavities are assumed to be illuminated by a normally incident plane wave. After a detailed description of the algorithm, we show theoretically the separate effects of dielectric and metal losses on the transmission coefficient of such cavities. We compare also simulation results to measurements, in the 60 GHz band, of resonant frequencies and Q factors of cavities with various mesh parameters.

The QPI (quasiparticle injection) devices have the most transistor-like characteristics in many superconducting three-terminal devices. In particular, Quiteron which operates with the principle of energy gap's suppression only to modulate the conductance of the output junction has a promising feature, such as a large gain, non-latching operation, and binary inversion. In this paper, we have investigated the behavior of the energy gaps to analyze the characteristics of the QPI devices. First we have introduced the nonequilibrium GL equation. Then we have derived a set of equations for QPI devices by using this equation. It is found that the energy gap of middle layer has the singularity under quasiparticle injection.

We have fabricated all-Nb thin film microbridges by nanometer process using new resist developed by us, electron beam lithography (EBL) and reactive ion etching (RIE) using CBrF3 gas. The resistance against CBrF3 plasma of this EB resist is 4-10 times as strong as poly-(methyl methacrylate) PMMA. The merit of RIE using CBrF3 gas is an anisotropic etching and high selectivity about resist and target. Trench of about 20 nm width was fabricated. Using this technique, the bridge with 40 nm length and 50 nm width was fabricated, and the thickness of bridge was 100 nm. The capacitance of the junction was estimated as 0.004 pF. Because of this small capacitance, fabricated samples are suitable for detection of submillimeter wave. The critical current Ic (T) of fabricated samples was proportional to (1T/Tc)3/2 like variable thickness bridge (VTB). Moreover, Shapiro step up to the 11th under the millimeter wave radiation (70 GHz) was observed.

We fabricated micro-contact Josephson junctions by self-alignment process, using double-layer-resist electron beam exposure and RIE. We chose Nb as superconductive materials. The junctions show the A.C. Josephson effect under the millimeter wave (70 GHz) radiation less than 100 µW and the 7th Shapiro step.

We successfully fabricated a very narrow gap in niobium film using electron beam lithography and RIE. The width of the gap was about 40 nm. We applied this process to the fabrication of Nb-PbIn-Nb planar Josephson junctions, and one of them showed the Dayem effect.