GaAs Lamb wave micro sensor

Acoustic Lamb Wave microsensors are suitable for label free sensing in liquid. The device relies on the interaction between acoustic waves propagating within a thin membrane and the liquid. Lamb wave sensors have been previously studied using AlN/Si structure to detect multi-parameters of a liquid, such as its temperature, density, sound velocity and viscosity using various modes as A₀ and S₀. These devices already showed good ability to perform measurements on fluids (gas or liquid) but in this case, chemical wet etching silicon was used to realize thin membranes combined with an Aln piezoelectric layer used to generate and detect the acoustic wave.

This paper reports the use of Gallium Arsenide as piezoelectric material to generate and propagate Lamb waves. GaAs material presents intrinsically interesting piezoelectric properties and is compatible with wet chemical etching process. The fabrication process allows producing a thin membrane but is also adapted for microfluidic microchannels. So, the same substrate can be used for the resonant structure and its excitation. The design of the resonant structure has been optimized using simulations to adapt the design of interdigital electrodes to the GaAs substrate taking into account the shear piezoelectric coefficient and its orientation. An experimental setup has been realized and measurements of the interaction with fluids are presented.