Fabrication of a high-T/sub c/ superconducting field effect transistor by ion beam sputtering

We have fabricated Au/SrTiO/sub 3/(STO)/YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) trilayer structures and superconducting field effect transistors (SuFETs). Insulating STO films were deposited by the ion beam sputtering (IBS) method at high oxygen pressure (/spl sim/10/sup -2/ Torr). (l00) peaks were observed in the X-ray diffraction (XRD) patterns of STO films deposited at temperatures higher than about 400/spl deg/C. The leakage current characteristics of a 400-nm-thick STO film were almost symmetric at different polarities and low leakage current of the order of 10/sup -9/ A was obtained up to around /spl plusmn/25 V at 4.2 K. The dielectric constant electric field product /spl epsiv//sub rS/E/sub BD/ of the STO film was estimated to be about 2.2/spl times/10/sup 8/ V/cm. In the SuFET fabrication process, a 10-nm-thick YBCO film covered with the STO layer was hardly degraded. The modulation of the normal state resistance of a sample almost corresponds to that of the induced carrier at positive bias. When a voltage of +20 V was applied to the gate electrode at 4.2 K, the current decreased by about 5% and the mutual conductance was 3.8 /spl mu/S at a drain voltage of 10 mV.