Thin film Ba0.25Sr0.75TiO3 voltage tunable capacitors on fused silica substrates for applications in microwave microelectronics

Thin film Au/Pt/Ba0.25Sr0.75TiO3/Pt/Au/Ti capacitor structures were fabricated on fused silica substrates using pulsed laser deposition of ferroelectric films. Low-field dielectric measurements were performed as a function of frequency in the range 1–25 GHz at different external dc fields up to 360 kV/cm. Resonant microwave power absorption observed at frequencies less than 10 GHz under dc field is due to electrostriction and field induced piezoelectric effects. The effects are simulated using an electroacoustic model of the multilayer capacitor structure. A circuit model is applied to investigate the influence of series resistance and inductance of interconnect/lead strips on capacitor performance. Analysis shows that the measured loss tangent of the capacitor is mainly due to series resistance and frequency dispersion of capacitance is caused by series inductance. The de-embedded value of the loss tangent is 0.005 at 10 GHz. The measured loss tangent is less than 0.02 and tunability is up to 40% in the whole frequency range. These parameters indicate high potential of Ba0.25Sr0.75TiO3 capacitors for applications in voltage controlled devices of microwave microelectronics.