Hiroshi Akoh

Josephson Junctions Consisting of all (103) Oriented YBaCuO/PrBaCuO/YBaCuO Trilayer Films

We have fabricated anisotropic Josephson junctions consisting of all (103) oriented YBa2Cu307-δ (140nm)/PrBa2Cu307-δ’ (45nm)/YBa2Cu307-δ (70nm) trilayer films. The trilayer films were fabricated on a whole (110) SrTi03 substrate by a reactive coevaporation method using pure ozone vapor. The entire process was carried out using standard photolithography technique. In order to reduce etching damages, all etching processes were performed using the Ar gas ECR dry etching with liquid nitrogen cooling, The typical current-voltage I-V characteristics for the junctions showed resistively shunted junction (RS J) like I-V characteristics with hysteresis. The junction with a dimension of 30x30 μm2 showed both Shapiro steps and Fraunhofer interference patterns. The junctions had anisotropic Fraunhofer interference patterns depending on the direction of the external magnetic field. This anisotropic property comes from the anisotropy in the magnetic penetration depth of (103) oriented YBaCuO films.

Fabrication of Small High- T c Trilayer Junctions Using Electron Beam Lithography

We have successfully fabricated YBa2Cu3O7-x/PrBa2Cu3O7-y/YBa2Cu3O7-x (YBaCuO/PrBaCuO/YBaCuO) trilayer junctions with a dimension of 1×1 µm2 using a direct electron beam lithography for the first time. The direct electron beam lithography was performed on the process of the junction definition to ensure the junction patterning with a small area. A double layer resist consisting of αM-CMS (500 nm) and PMMA (1 µm) was used, since the double layer resist has a high aspect ratio and is removed easily by dipping in acetone. The junction with a dimension of 1×1 µm2 and a barrier thickness of 25 nm had the resistively shunted junction (RSJ)-like I-V characteristic at 4.2 K. In addition, the critical current I c was observed to be modulated by the external magnetic field. These results suggest that the fabrication process using the electron beam lithography with the double layer resist is a suitable method for the fabrication of high-T c superconducting trilayer junctions with small dimensions.

Photosensitive Josephson junction with hydrogenated amorphous silicon barrier

Abstract Photosensitive Josephson junctions with hydrogenated amorphous silicon barriers have been fabricated. The maximum Josephson current is found to increase under irradiation of HeNe laser pulses.