Biepitaxial Josephson junctions and SuFET technology for the preparation of HTS-JoFETs

Biepitaxial Josephson junctions and superconducting field effect transistors (SuFET) were fabricated in order to combine both techniques to a Josephson junction field effect transistor (JoFET). The Josephson junctions show RSJ-like behaviour. At 30 K a critical current density of J, = lo4 A/cm2 and an LRN-product of 0.1 mV were obtained. The oscillation of Shapiro steps with applied microwave field can be well fitted by the RSJ-model. SuFETs with CeO2 as dielectric show, for fixed charge transfer, results comparable to SrTiO8-based SuFETs. The downset of the resistive transition of a six-unit-cells thick YBa2Cu307-6 layer is 44 K and the largest field effect obtained so far is 1.5 %. Prelimary results on JoFETs show a drastic change in the critical current density and in the specific junction resistance, however the I,RNproduct remains still in the typical range. The insulating properties are degraded compared to SuFETs.