Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators

Tunable 5.2 GHz bulk acoustic wave resonators utilizing BaxSr1-xTiO3 ferroelectric films with similar intrinsic properties but different interface roughness are fabricated and characterized. Increase in roughness from 3.2 nm up to 6.9 nm results in reduction in Q-factor from 350 down to 150 due to extrinsic acoustic losses caused by wave scattering at reflections from rough interfaces and other mechanisms associated with roughness. The increased roughness is a result of distortion of Pt bottom electrode caused by formation of heterogeneous enclosures of TiO2-x in the Pt layer. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610513]