FEM simulation study on mass loading sensitivity of high aspect ratio nano-pillar sensing medium in SAW sensors

Mass loading effect of a thin film is one of the prime sensing principles in surface acoustic wave (SAW) sensors. Recently we reported mass loading effect of a high aspect ratio resonant structure such as a nano-pillar attached normal to the surface of the SAW resonator. When resonance frequency of the pillar is closer to SAW resonator frequency the resonance frequency shift caused by mass loading of the pillars tends to a negligible value. The high aspect ratio structure and the SAW resonator together in unison form a system of coupled resonator. More recently we reported employing high aspect ratio nano-pillars as sensing medium to design high sensitive SAW sensors such as a SAW hydrogen sensor. In this paper we present finite element method (FEM) simulation study of a SAW resonator with nano-pillars as sensing medium and report the significance of cross-section of resonant pillars on sensitivity. The simulation results shows the mass loading sensitivity of the smaller cross-section pillars are significantly higher. Further the results show that if the pillars cross-section is in nano scale, there is more chance of positive resonance shift at smaller heights and the sensitivity is higher for small change in dimensions of the pillar.