Tunable SrTiO(3) varactors using parallel plate and interdigital structures

The dielectric properties of SrTiO(3) (STO)/YBCO and STO films deposited on LaAlO(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 deg C; higher temperatures resulted in interfacial degradation and poor film quality, and lower temperatures resulted in films with lower dielectric constants (epsilon(r)) and tunabilities. Interdigital varactors comprised of STO films deposited directly on LaAlO(3) displayed higher tunabilities and significantly lower losses