Abstract
This paper presents DC voltage dependent thin film bulk acoustic wave resonators (FBARs) based on ferroelectric barium strontium titanate (BST). The electrostrictive effect in BST film that enables the resonances to switch on and off with dc bias is discussed. Composite BST FBARs that consist of BST, platinum (Pt), silicon (Si), and oxide (SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) layers are discussed by comparing with the conventional FBAR structure. For composite FBARs, the BST layer is primarily used for transduction while the Si and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layers are used to increase the overall quality factor (Q). Measurement results of a composite FBAR show a Q that exceeds 600 at its parallel resonance frequency of 2.169 GHz and an electromechanical coupling coefficient of 0.68%.
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