Shuichirou Yamamoto, Atsushi Kawaguchi and Shunri Oda
Research Center for Quantum Effect Electronics, Tokyo Institute of Technology,
O-Okayama, Meguro-ku, Tokyo 152, Japan

We have observed anomalous current-voltage characteristics related to intrinsic Josephson junction along c-axis of YBaCuO thin films.
180nm thick c-axis oriented YBaCuO films are deposited on SrTiO3(100) substrates by MOCVD at 650℃. To reduce Josephson coupling between CuO2 planes, these films are annealed at 500℃ and 2Torr of a gaseous mixture 1:1 oxygen and argon for 1hour. After annealing these films are immediately transferred to a metal evaporation system and 90nm-thick Au capping layer is deposited. Samples are coated with positive photo-resist and small mesa structures of 5μm x 5μm are fabricated by optical lithography. These mesas are re-shaped to 1.5μm x 1.7μm mesas by AFM lithography. Ar+ ion milling is performed to etch the Au capping layer and 35nm of YBaCuO layer. Further, these samples are coated with 300nm thick layer of photo-resist which serves as an insulator film. Au contact pads are fabricated by AFM lithography and Au deposition. Three terminal current-voltage measurement shows a clear hysteresis around 280μA with a maximum current height of 30μA. A number of steps could be observed both in the hysteresis loop and in the degenerate portion of current-voltage curve. The maximum width of each steps is about 2mV at 5K. These observations could be summarized as an effect of series connection of intrinsic Josephson junctions. Above 20K hysteresis disappeared. On the other hand, the steps could be observed up to 30K.
 

Int. Symp. Intrinsic Josephson Effect and THz Plasma Oscillations in High Tc Superconductors; 国際会議; (1997)