S_0 Lamb wave resonators for in-liquid sensing: promising alternative to shear bulk acoustic wave devices

摘要

Sensors capable of in-liquid operation are of primary importance not only for biosensors applications but also for liquid monitoring. Thin film electroacoustic (TEA) devices have emerged as promising choice for such applications. The most common TEA devices are the thin film bulk acoustic wave resonator (FBAR) and the Lamb wave resonator (LWR). FBAR operating on the shear mode have been widely studied in view of biosensors applications. A theoretical framework describing the in-liquid sensitivity features of LWR employing the S_0 mode (S_0-LWR) has been experimentally proven recently. However, a comparison between both devices has not been performed yet. Here we theoretically and experimentally compare AI??N-based S_0-LWR and FBARs on their solidly mounted modality (SMR), in terms of their in-liquid sensitivity features at similar frequencies. So-LWR prove to be slightly more sensitive to the density and viscosity of the liquids. Moreover, if a metallic bottom electrode is not deposited on their backside they can also sense variations in the dielectric permittivity of the liquid, which cannot be done with common SMRs.