Surface acoustic wave resonator characterization for gas and liquid detection

Abstract

Surface Acoustic Wave (SAW) resonators have garnered significant interest in recent years due to their advantageous properties, including high Q-factor, low power consumption, and compact size, making them ideal candidates for various sensor applications. SAW resonators can be used as material detection devices since manipulations to the substrate along the delay line can alter the characteristics of the device. The objective of the study is to determine the characteristics of a SAW resonator based network when it is exposed to gasses and liquids for sensor applications. Several versions of PCBs are manufactured for the resonator measurements. These PCBs are customized according to the shape of the resonator. Some of the PCBs are then further customized to incorporate multiple signal lines from the same resonator with the help of switches. Resonators are wire bonded in order to connect them to PCBs thus reducing the chances of damaging during measurements. Wire bonding process was optimized through experimentation with already damaged wafers or test wafers. Through the use of a Vector Network Analyzer (VNA), S parameter information were obtained under different conditions for various resonators. Firsly VNAs were calibrated for desired frequency range and parasitic cable effects were removed. Measurements for resonators were taken as a baseline with just the bondwires and the PCB. Same measurements were repeated in a Faraday cage with lights turned off to see the effects of light and noise on the resonator. Resonators were then coated with 2 different sensing materials Phthalocyanine and Polyvinylpyrrolidone (PVP). After coating the resonators same measurements were repeated on both bandpass and bandstop filtering behavior resonators to acquire data. Acquired data were then used to create a model filter then simulated with Colpitts Oscillator configuration to see frequency selectivity. The results showed that noise and light effects were minimal on the resonators since data from Faraday cage and baseline measurements were almost identical. It was observed that even coating resonators with a sensing material changed the behavior of the resonator within the ranges of the kilohertz. Additionally, since PVP also interacts with moisture, the effectiveness of the coating was observed by blowing on to the resonator and observing frequency shifts.