Highly sensitive thick diaphragm-based surface acoustic wave pressure sensor

Abstract

Diaphragm-based Surface acoustic wave (SAW) pressure sensors are of great interest to fulfill high-pressure sensing requirements in industrial and commercial applications. These sensors are developed with a thick diaphragm, can endure considerable pressure but adversely result in low sensitivity and affect device accuracy. The trade-off between diaphragm thickness and sensitivity is the major problem in designing pressure sensors for high-pressure sensing ranges. This work proposed a highly sensitive pressure sensor design based on one port SAW resonator with AlN/Mo/SOI multilayer structure. The sensor utilizes a 50 μm thick rectangular diaphragm and has been fabricated with simple microfabrication techniques, making it cost-effective and easy to implement in pressure sensing equipment. Finite element analysis (FEA) has been performed for analyzing diaphragm to locate IDTs based on bending, uniformity of stress distribution and induced strain type. The developed sensor exhibits good performance characteristics, including high sensitivity (up to 129.17 ppm/MPa), wide pressure sensing range (up to 2 MPa), and good repeatability with linear behavior for applied pressure range. Additionally, this work has presented a novel approach to enhance pressure sensitivity based on increased velocity without compromising sensing range. The obtained sensitivity has been enhanced up to 228.46 ppm/MPa by modifying the primarily developed sensor design such that the SAW propagation direction becomes parallel to the induced strain direction. With the proposed novel concept, the sensitivity has been significantly improved by 76.87 % compared to the primarily developed sensor. Besides improved sensitivity, the modified sensor also shows the best repeatability and linearity. All these performance characteristics pave the way to make this design a good choice for high-pressure sensing applications.