Numerical Investigation of Rayleigh, Sezawa and Love Modes in C-Axis Tilted ZNO/SI for Gas and Liquid Multimode Sensor

Abstract

Finite element analysis is carried out to investigate the characteristics of Rayleigh, Sezawa and Love surface acoustic modes travelling along c-axis tilted ZnO layer on Si (001) half-space. The phase velocity dispersion curves, electromechanical coupling, reflectivity and mass loading sensitivity are studied for different electroacoustic coupling configurations and c-axis tilt angles θ. The behavior of Rayleigh and Sezawa modes operating as gas sensor, was simulated under the hypothesis that the ZnO free surface is covered with a thin polyisobutylene (PIB) film, 0.2 μm thick, able to selectively adsorb volatile gases at atmospheric pressure and room temperature. The sensor sensitivity to gas concentration in air, i.e. the frequency shifts per unit gas concentration, is studied and compared to some common materials used in literature. The obtained results, demonstrate the feasibility of high-frequency multimode micro-sensor based on the c-axis tilted ZnO piezoelectric thin film and operating in both liquid and gaseous environments.

A review of piezoelectric MEMS sensors and actuators for gas detection application

“…Moreover, there are basically three common modes of SAWs devices that are extensively utilized for gases and chemicals detection, namely Rayleigh wave mode [ 203 ], Lamb wave mode [ 204 ], and shear horizontal wave mode (SH-SAWs) [ 205 ]. In addition, most of the reported SAW gas and microfluidic sensors are based on the Rayleigh waves mode [ 206 , 207 ], whereas the shear horizontal and Lamb wave SAWs are only suitable for gas sensors, but they are not able to perform the detection in the microfluidic or liquid-based sensing environment due to the fact that the wave propagation in the shear horizontal mode and its displacement is only parallel with the substrate surface, which inhibits the wave vibration into the liquid on the surface [ 181 ].…”

Electro-Acoustic Properties of Scandium-Doped Aluminum Nitride (ScxAl1-xN) Material and its Application to Phononic Crystal-Coupled SAW Devices

“…The result is reported in Figure 14a, which shows that the insertion loss (S 21 ) is affected by the c-axis tilting. The variation in the insertion loss is directly linked to the electromechanical coupling coefficient, which is very sensitive to the tilted angle [90]. Finally, using the values of the elastic constants Cij (Figure 4a), and the piezoelectric eij (Figure 4b) and dielectric values ɛij (Figure 4c), the dependence of the insertion loss (S21) of the SAW delay line without PnCs versus the c-axis tilted angle (θ°) of Sc0.375Al0.625N was examined for θ = 20°, 40°, 60° and 80°, and compared to that when the c-axis is normally oriented (θ = 0°).…”