Microwave dielectric properties of ferroelectric BaTiO3 thin film

Abstract

The dielectric properties of c-axis epitaxial BaTiO3 thin film on LaAlO3 are investigated at frequencies of 0.5-30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 gm wide and spaced 2 mum apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 mum. The capacitance of epitaxial BaTiO3 films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO3 film with a finger length of 80 mum due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/omegaCR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO3 film has a tunability [defined as k(V) = [C(0) - C(V)]C(0)] of 1.5% at 15 V, a loss tangent of less than or equal to0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO3 film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO3 capacitor, the tetragonality (c/a) of epitaxial BaTiO3 film and design of interdigital capacitor should be modified.