Fabrication and properties of field effect device based on bi-crystal grain boundary junction of YBa2Cu3O7-δ films
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The electric field effects on bi-crystal YBa2Cu3O7-(delta ) grain boundaries were studied. The field effects were examined for an inverted MIS structure sample, in which a channel was arranged across the grain boundary on the SrTiO3 bicrystal substrate served as an insulator with the thickness of 50 micrometers . The field-induced change in the normal resistance was enhanced not only by an increase in the dielectric constant of gate insulator but also by a reduction in the carrier density nearby the grain boundary. For the sample with the YBCO thickness of 1,000 angstroms, the gate voltage of 80 V corresponding to 2 X 104 V/cm induced the relative changes in the normal resistance up to around 5%. The grain boundary junctions showed hysteretic I-V properties and sub-gap structures caused by the self-excited resonance of ac Josephson effect. Significant field effects on the hysteresis and sub-gap structures were observed. These effects were attributable to the field-induced changes in dielectric properties of the grain boundary. It was apparent that the effective dielectric constant of the grain boundary was several tens and decreased with increasing gate voltages.