%0 Journal Article
%T The Liquid Sensor Using Thin Film Bulk Acoustic Resonator with C-Axis Tilted AlN Films
%A Ying-Chung Chen
%A Wei-Tsai Chang
%A Kuo-Sheng Kao
%A Chun-Hung Yang
%A Chien-Chuan Cheng
%J Journal of Nanomaterials
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/245095
%X Dual-mode thin film bulk acoustic resonator (TFBAR) devices are fabricated with c-axis tilted AlN films. To fabricate dual-mode TFBAR devices, the off-axis RF magnetron sputtering method for the growth of tilted piezoelectric AlN thin films is adopted. In this report, the AlN thin films are deposited with tilting angles of 15¡ã and 23¡ã. The frequency response of the TFBAR device with 23¡ã tilted AlN thin film is measured to reveal its ability to provide dual-mode resonance. The sensitivities of the longitudinal and shear modes to mass loading are calculated to be 2295£¿Hz£¿cm2/ng and 1363£¿Hz£¿cm2/ng with the mechanical quality factors of 480 and 287, respectively. The sensitivities of the longitudinal and shear modes are calculated to be 0 and 15£¿Hz£¿cm2/¦Ìg for liquid loading. 1. Introduction Surface and bulk acoustic resonator devices are attracting increasing attention owning to their use in various novel sensors, including UV sensors, mass sensors, biosensors, and others [1¨C3]. Surface acoustic resonators have been developed and examined for potential sensor applications because they are cheap and small. However, surface acoustic resonators suffer from high insertion loss and poor power handling. Therefore, thin film bulk acoustic resonator (TFBAR) devices have been studied globally; they have a low insertion loss, a high power handling capability, small size, and high sensitivity [4¨C6]. Lakin classified FBAR devices into three types, which were via-isolated resonators, air gap-isolated resonators, and solidly mounted resonators [7]. The general purpose of these structures is to form a free or clamped interface beneath the resonance zone. This work develops a dual-mode TFBAR device based on an adapted via-isolated resonator with piezoelectric thin film whose c-axis is tilted. The back-etched cavity is used as the sensing area. Despite the use of various piezoelectric films in TFBAR devices, including PZT, ZnO, and AlN thin films [8¨C12], most of the many studies of piezoelectric thin films have focused on PZT piezoelectric materials. However, the use of PZT is limited for environmental reasons [13, 14]. Hence, ZnO and AlN thin films have become the most promising materials for piezoelectric applications. This study concerns piezoelectric thin films of AlN, whose high quality factor makes them useful for elucidating the sensing properties of TFBAR for liquids. TFBAR has two major resonance modes longitudinal and shear. The longitudinal mode is typically used when TFBAR is utilized as a communication device at high operating frequencies. For biosensor
%U http://www.hindawi.com/journals/jnm/2013/245095/