Love-Mode MEMS Devices for Sensing Applications in Liquids.

Cinzia Caliendo,Fouad Boubenider,Smail Sait

doi:10.3390/mi7010015

Abstract

Love-wave-based MEMS devices are theoretically investigated in their potential role as a promising technological platform for the development of acoustic-wave-based sensors for liquid environments. Both single- and bi-layered structures have been investigated and the velocity dispersion curves were calculated for different layer thicknesses, crystallographic orientations, material types and electrical boundary conditions. High velocity materials have been investigated too, enabling device miniaturization, power consumption reduction and integration with the conditioning electronic circuits. The electroacoustic coupling coefficient dispersion curves of the first four Love modes are calculated for four dispersive coupling configurations based on a c-axis tilted ZnO layer on wz-BN substrate. The gravimetric sensitivity of four Love modes travelling at a common velocity of 9318 m/s along different layer thicknesses, and of three Love modes travelling at different velocity along a fixed ZnO layer thickness, are calculated in order to design enhanced-performance sensors. The phase velocity shift and attenuation due to the presence of a viscous liquid contacting the device surface are calculated for different thicknesses of a c-axis inclined ZnO layer onto BN half-space.

Highlights

Chemical sensors based on the propagation of surface acoustic waves (SAWs) are usually based on a delay line or resonator configuration with the acoustic wave path covered by a membrane sensible to a specific target analyte
We theoretically studied the propagation of Loveimproved wave along theperformances surface of some can be achieved by choosing a proper layer thickness, which increases the sensitivity of the device piezoelectric substrates (AlN, InN, ZnO, GaN, ST quartz): the phase velocity and the electroacoustic towards changes in physical properties at its surface, including mass loading
Love wave devices are more robust, can operate in a harsh environment and have operation capability on a wireless platform, which makes it possible to operate these devices from a remote location

Summary

Introduction

Chemical sensors based on the propagation of surface acoustic waves (SAWs) are usually based on a delay line or resonator configuration with the acoustic wave path covered by a membrane sensible to a specific target analyte. In order to increase the Love wave velocity and K with respect to those obtained for single piezoelectric substrates (AlN, InN, ZnO, GaN, ST quartz): the phase velocity and the electroacoustic material substrates, we investigated a dispersive structure consisting in a thin piezoelectric ZnO coupling coefficient (K2) were calculated for different c-axis tilt angles with respect to the surface layernormal. Themodes weak piezoelectric piezoelectric coupling of this material wave velocity and is the This layer can be improved by covering the free surface of the quartz substrate with a thin SiO2 layer. With increasing the Love mode order, ever decreasing K2 values can be reached by the four coupling configurations: the SMFT of the first mode reaches the highest K2 value since the metallization on the ZnO side opposite the IDTs strongly enhances the vertical electric field in the ZnO layer.

Gravimetric Sensitivity

Viscosity Sensitivity

B 2 u2

Conclusions