Lateral field excited LiTaO<inf>3</inf> acoustic wave sensing platform

Abstract

Figure 1 (a) Top view (sensing surface) of a standard QCM sensor and (b) top view (sensing surface) of a LFE sensor; shaded and dotted regions are gold. Dotted regions indicate reference (bottom) side while shaded regions indicate sensing (top) side Abstract-AT-cut quartz is the standard material used in the quartz crystal microbalance (QCM) due to the existence of a temperature compensated pure transverse shear mode (TSM). In the QCM the TSM is excited by electrodes on both the top and bottom surfaces of the quartz wafer resulting in what is called thickness field excitation. When used for sensor applications the QCM has several deficiencies.First, quartz is weakly piezoelectric and second the sensing surface has deposited metal electrodes which can interfere with the detection of a target analyte. Another common piezoelectric crystal, LiTaO 3 , offers an interesting alternative since it has significantly higher piezoelectric coupling than quartz and the possibility of realizing a temperature compensated TSM. Further the TSM can be excited by lateral field excitation (LFE) which leaves the top surface bare. It is the purpose of this paper to theoretically and experimentally investigate the potential of using LiTaO 3 as a new LFE BAW sensor platform.