Tunable BiFeO3-BaTiO3 thin film bulk acoustic wave resonators for microwave applications
Paper in proceedings, 2012
The electrically tunable thin film bulk acoustic wave resonators (FBARs), utilizing electric field induced piezoelectric effect in paraelectric phase ferroelectrics have been demonstrated recently. They enable development of novel reconfigurable/adaptable microwave circuit architectures. One may expect enhanced functionalities in the FBARs utilizing multiferroic materials due to the coupling interaction between ferroelectric and ferroelastic order parameters. Additionally, coupling with magnetic phenomenon would allow development of the FBARs tunable by both electric and magnetic field which enable a variety of other advanced applications. In this work the single-phase 0.67BiFeO3-0.33BaTiO3 multiferroic thin film solidly mounted FBAR test structures have been fabricated and characterized. The FBAR test structures reveal resonance at 4.5 GHz, 3% tunabilty of the resonant frequency and an electromechanical coupling coefficient of 6% at 10 V dc bias. These parameters are highest for the electrically tunable FBARs reported so far. The irreversible changes of the resonant frequency with electric field are less than 0.1%. The relatively low Q-factor, below 100, is associated with wave scattering from rough interfaces and may be improved by the design/technology optimization.