Paraelectric thin films for microwave applications

We have designed, fabricated and characterized electrically tunable and adaptive microwave devices incorporating paraelectric thin films of Sr_0.5Ba_0.5/TiO₃ (SBTO) and SrTiO₃ (STO) on 1 cm × 1 cm × 0.5 mm LaAlO₃ substrates. The paraelectric layer thickness for these devices varied between 0.5 μm and 2 μm. We used normal metal Au and superconducting YBa₂Cu₃O_7-x top electrodes for SBTO and STO devices, and operated them at room- and cryogenic-temperatures, respectively. The microwave devices included voltage-tunable resonators, voltage-tunable phase shifters, voltage-tunable mixers, and voltage-tunable filters. Under dc voltage bias, these compact planar devices exhibited up to 30% resonant frequency modulation, about 1°/mm-GHz phase shift, more than 40 dB change in mixed microwave power, and fine-tunable symmetric filter profile with less than 2% bandwidth and more than 15% adaptive range.