Tunable SrTiO/sub 3/ varactors using parallel plate and interdigital structures

The dielectric properties of SrTiO/sub 3/ (STO)/YBCO and STO films deposited on LaAlO/sub 3/ substrates were evaluated, for potential varactor applications wherein the capacitance is altered via a dc voltage applied across the STO film. The optimal growth temperature for the STO films in the STO/YBCO structures was 800/spl deg/C; higher temperatures resulted in interfacial degradation and poor film quality, and lower temperatures resulted in films with lower dielectric constants (/spl epsi//sub r/) and tunabilities. Interdigital varactors comprised of STO films deposited directly on LaAlO/sub 3/ displayed higher tunabilities and significantly lower losses.