FABRICATION OF A HIGH-T-C SUPERCONDUCTING FIELD-EFFECT TRANSISTOR BY ION-BEAM SPUTTERING

We have fabricated Au/SrTiO3(STO)/YBa2Cu3O7-x (YBCO) trilayer structur es and superconducting field effect transistors (SuFETs). Insulating S TO films were deposited by the ion beam sputtering (IBS) method at hig h oxygen pressure (similar to 10(-2) Torr), (l 00) peaks were observed in the X-ray diffraction (XRD) patterns of STO films deposited at tem peratures higher than about 400 degrees C. The leakage current charact eristics of a 400-nm-thick STO film were almost symmetric at different polarities and low leakage age current of the order of 10(-9) A was o btained up to around +/-25V at 4.2K. The dielectric constant electric field product epsilon(rS)E(BD) of the STO film was estimated to be abo ut 2.2x10(8)V/cm. In the SuFET fabrication process, a 10-nm-thick YBCO film covered with the STO layer was hardly degraded. The modulation o f the normal state resistance of a sample almost corresponds to that o f the induced carrier at positive bias. When a voltage of +20V was app lied to the gate electrode at 4.2K, the current decreased by about 5% and the mutual conductance was 3.8 mu S at a drain voltage of 10mV.