FABRICATION OF BA1-XSRXTIO3 TUNABLE CAPACITORS WITH TL2BA2CA1CU2OX ELECTRODES

Tunable coplanar Ba1-xSrxTiO3 (BSTO) thin-film capacitors with superco nducting Tl-Ba-Ca-Cu-O (2212) electrodes have been successfully prepar ed using RF sputtering onto LaAlO3 (100) substrates. The capacitors we re fabricated in a five-step process consisting of: deposition of a Ba 2CaCu2Ox precursor films on LaAlO3 substrates; patterning of the precu rsor film into a planar capacitor with a gap of 5 to 40 mu m; formatio n of the superconducting phase by vapor-phase reaction with thallium; deposition of an amorphous BSTO overlayer onto the gap; and finally po st-deposition annealing of the BSTO layer in flowing oxygen. The detai ls of each fabrication step are presented. In addition, the structure, microstructure and composition of the films are analyzed. The tempera ture- and the voltage-dependence of the low frequency (10 kHz-100 kHz) capacitance and loss tangent are presented. A tunability of 10% at 77 K and 100 kHz was achieved. The capacitance-tunability results are co mpared with those obtained from YBCO-BSTO-YBCO capacitors.