Highly Mass-Sensitive Thin Film Plate Acoustic Resonators (FPAR)

Lilia Arapan,Ivan D Avramov,Ventsislav Yantchev,Gergana Alexieva,Ekaterina Radeva,Ilia Katardjiev,Vesseline Strashilov

doi:10.3390/s110706942

Abstract

The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with hexamethyl-disiloxane(HMDSO)-plasma-polymerized thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented. FPARs demonstrate high mass-loading sensitivity as well as good tolerance towards the HMDSO viscous losses. Initial measurements in gas phase environment are further presented.

Highlights

A variety of physical, chemical and recently biochemical sensors based on the gravimetric principle utilizing electroacoustic devices have been around for years
As the wave field of surface acoustic waves (SAW) is confined to the vicinity of the substrate surface, their propagation characteristics become sensitive to any kind of surface perturbation and to mass loading
To strengthen this point we further considered a comparison of the film plate acoustic resonators (FPAR) gas sensitivity to that reported for other HMDSO-coated resonant devices using different types of acoustic modes

Summary

Introduction

A variety of physical, chemical and recently biochemical sensors based on the gravimetric principle utilizing electroacoustic devices have been around for years. The detection is performed in either delay-line or resonator-stabilized oscillation, the latter being preferred in gas sensing due to the higher Q and lower device loss resulting in substantial noise reduction and resolution improvement. At present, these sensors are well known. Thin film bulk acoustic resonators (FBAR) operating in the lower GHz range, employed in silicon-integrated miniaturized gas sensors, have demonstrated high mass sensitivity [9,10]. In this paper we study the mass sensitivity and the applicability of thin film plate acoustic resonators (FPAR) in gas sensing applications. The results are further supported by measurements in gas phase environment

Theoretical Considerations

FPAR Experimental Loading by pp-HMDSO

Gas Sensitivity Experiments

Conclusions