Microacoustic in-liquid sensors based on thin AlN films: A comparative study

Environmental and health monitoring have become crucial the last decades. In-liquid sensing plays an important role for this kind of monitoring. Exhaustive studies have been going one in order to improve the sensing devices. Sensors based on thin film electroacoustic (TEA) devices have emerged as a promising alternative to quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensors. TEA devices include quasi shear mode film bulk acoustic resonators (QS-FBAR) and S₀ mode Lamb wave resonators (S₀-LWR) based on AlN films. These devices offer miniaturization and easy integration. For a better understanding of their physical behavior, we present a comparative study on their sensing mechanisms in liquid media. For this study we employed finite element analysis (FEA). QS-FBARs behave as pure shear resonators, sensing viscosity and density in a non-distinguishable manner. However, S₀-LWRs demonstrate different sensitivities to liquid viscosity and density. Their different in-liquid sensitivities offer the possibility to combine them and measure independently changes in density and viscosity.