Intrinsically switchable, high-Q ferroelectricon-silicon composite film bulk acoustic resonators.

This paper presents a voltage-controlled, highquality factor (Q) composite thin-film bulk acoustic resonator (FBAR) at 1.28 GHz. The composite FBAR consists of a thin layer of barium strontium titanate (BST) that is sandwiched between two electrodes deposited on a silicon-on-insulator (SOI) wafer. The BST layer, which has a strong electrostrictive effect, is used for electromechanical transduction by means of its voltage-induced piezoelectricity. The silicon layer, with its low mechanical loss, increases the Q of the resonator. The composite FBAR presented here exhibits Qs exceeding 800 with a resonance frequency and Q product (f × Q) of 1026 GHz.