HTS/ferroelectric thin films for tunable microwave components

We report on the electrical characterization of Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///LaAlO/sub 3/ multilayer structure. This structure was fabricated using a pulsed laser deposition technique yielding film thicknesses of 300 nm and 800 nm for the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) and the Ba/sub 0.5/Sr/sub 0.5/TiO/sub 3/ (BST) films, respectively, A transition temperature T/sub c/=91.5 K was measured for the YBCO film in this structure after deposition of the BST layer. The structure was patterned into parallel plate capacitors with 400/spl times/400 /spl mu/m gold contacts and YBCO electrodes on top and underneath the BST, respectively. A relative dielectric constant (/spl epsiv//sub r/)/spl sim/425 and a loss tangent (tan/spl delta/)=0.010 were measured at 1.0 MHz at 298 K and zero dc voltage (V/sub dc/=0 volts). At 77 K, the dielectric data showed 320/spl les//spl epsiv//sub r//spl les/360 and tan/spl delta/=0.036 at V/sub dc/=0 volts. For 5.0/spl ges/V/sub dc//spl ges/-3.0 volts /spl epsiv//sub r/ could be varied from 180 to 370. For -5.0/spl les/V/sub dc//spl les/-3.0 volts, /spl epsiv//sub r/ decreased rapidly with little change in tan/spl delta/. The /spl epsiv//sub r/ versus V/sub dc/ data suggest that changes in /spl epsiv//sub r/ were affected by electrode space charge layers.<>