A LN/Si-Based SAW Pressure Sensor

Abstract

Surface Acoustic Wave (SAW) sensors are small, passive and wireless devices. We present here the latest results obtained in a project aimed at developing a SAW-based implantable pressure sensor, equipped with a well-defined, 30 μm-thick, 4.7 mm-in-diameter, Lithium Niobate (LN) membrane. A novel fabrication process was used to solve the issue of accurate membrane etching in LN. LN/Si wafers were fabricated first, using wafer-bonding techniques. Grinding/polishing operations followed, to reduce the LN thickness to 30 μm. 2.45 GHz SAW Reflective Delay-Lines (R-DL) were then deposited on LN, using a combination of e-beam and optical lithography. The R-DL was designed in such a way as to allow for easy temperature compensation. Eventually, the membranes were etched in Si. A dedicated set-up was implemented, to characterize the sensors versus pressure and temperature. The achieved pressure accuracy is satisfactory (±0.56 mbar). However, discontinuities in the response curve and residual temperature sensitivity were observed. Further experiments, modeling and simulations were used to analyze the observed phenomena. They were shown to arise essentially from the presence of growing thermo-mechanical strain and stress fields, generated in the bimorph-like LN/Si structure, when the temperature changes. In particular, buckling effects explain the discontinuities, observed around 43 °C, in the response curves. Possible solutions are suggested and discussed.

Trends and Applications of Surface and Bulk Acoustic Wave Devices: A Review

“…SAW devices are also good candidates for pressure and temperature sensing [ 63 , 64 , 65 , 66 ]. In the Rodríguez-Madrid et al [ 66 ] study, a SAW-based pressure sensor was reported with a sensitivity of 0.33 MHz/bar, a working frequency between 10 to 14 GHz with high-order harmonic acoustic modes.…”

Corrosion Sensors for Structural Health Monitoring of Oil and Natural Gas Infrastructure: A Review

“…Alternately, when the SAWs reach grating reflectors, they get reflected back to the emitting IDT for RF signal processing (Figure 20b) [228,229]. SAW-based sensing is accomplished by measuring changes in the phase velocity and/or amplitude of the waves caused by property changes in the propagation path such as temperature, mass, electrical, and mechanical changes; therefore, SAW sensors can be employed for monitoring many physical parameters (e.g., temperature [213,230,231,232], pressure [233,234], and strain [235,236]) as well as chemical species in the gaseous and aqueous phases. Detailed reviews on fundamentals of sensing mechanisms and applications can be found in References [228,229,237].…”

On the performance of PVDF based piezoelectric sensor with microstructures

“…Surface acoustic wave sensor (SAW) is a microelectromechanical system (MEMS) that utilizes the propagation of acoustic waves to detect the presence and concentration of the analyte. SAW sensors are extensively used for detecting physical quantities such as strain, pressure, and temperature [3][4][5][6] . Among different gas detection sensors, SAW exhibits excellent response time, small size, low cost, ability to work in wired and wireless mode, and is mainly compatible with modern fabrication technologies.…”