Temperature stable Ba xSr1-xTiO 3 thin film structures for microwave devices

Bilayer structures of Ba_0.25Sr_0.75TiO₃/Ba_0.75Sr_0.25TiO₃ were deposited in-situ on MgO substrates using pulsed laser deposition. To investigate the electrical properties, interdigital capacitor structures were patterned on the top of the film using photolithography followed by ion-milling processes. The capacitance and the tunability of the structures were measured between 100 and 400 K in the frequency range 1 to 3 GHz. The temperature coefficient of capacitance was evaluated and compared against the same structure patterned on a Ba_0.5Sr_0.5TiO₃ thin film. The dielectric constant of the thin film was evaluated using a conformal transformation. It was seen that the bilayer structure had a much improved temperature coefficient of capacitance but a lower dielectric constant.