Mitsuo Kawamura

Nb-Pb-Nb Planar Josephson Junction Fabricated by RIE

Nb-Pb-Nb planar Josephson junctions were fabricated by electron-beam exposure and Reactive-Ion-Etching (RIE) and their response characteristics under millimeter-and submillimeter-wave radiation were investigated. The size of the weak-link was 0.67-1.0 micrometers long, 5.0 micrometers wide and 1000A thick. The fourth Shapiro step under 70 GHz millimeter-wave radiation could be observed. On the other hand, the planar junctions showed only a bolometric response under 891 GHz submillimeter-wave radiation. In this paper, the characteristics of RIE using a CBrF3 gas as the etchant and an electron beam resist, PMMA, as the mask material are also discussed.

Josephson triode and its characteristics

Abstract Single micro-contact type Josephson junctions and Josephson triodes composing of three micro-contact type junctions have been investigated with the purpose of its usage for the sensitive heterodyne mixing device. These devices have been fabricated by the self-alignment technology, and the experimental results for the properties for the fabricated devices were reported. It was especially shown that the fabricated triode has revealed some of the fundamental properties as the Josephson triode. Numerical calculations also have been carried out and were in agreement to some extent with the experimental results.

Operational characteristics of an RF-excited CW-HGN laser

Abstract Experimental studies of an inductively coupled RF-excited CW-HCN laser have been carried out. A maximum output power of 160mW in CW at 337 μm has been obtained using a laser tube 1 m long and 55mm inner dia.

All-Nb thin film microbridge-type Josephson junction for submillimeter-wave detection

Abstract A copolymer of methyl methacrylate (MMA) and 3-triethoxysilylpropyl methacrylate (ESPMA) was proposed as a positive-working electron beam (EB) resist of a new type. It was found that it had 4–10 times the resistance of polymethylmethacrylate (PMMA) against CBrF3 plasma damage. The mechanism of etching Nb in reactive-ion-etching (RIE) was deciphered. Using the new EB resist and nanometer process technology, an all-Nb thin film microbridge was fabricated. It shows the a.c. Josephson effect, i.e. the Shapiro steps upto the 11th were observed under millimeter-wave (70 GHz) radiation. In addition the coherently working performance of the series array of these thin-film microbridges were observed definitively.

Analysis of quasiparticle injection three-terminal device

Abstract 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 suppression of the energy gap 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. Current-voltage characteristics of QPI device is calculated by using these values of the energy gaps. 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 and the QPI device may have a large gain for suitable junction resistances.