High Frequency SAW Resonator Design, Simulation, and Optimization With Applications to Chemical Gas Sensors Open Access
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Surface Acoustic Wave (SAW) resonators with a high resonate frequency have a great sensitivity to detect the load mass change in real time which shows the promising potential in sensing fields, such as gas detection and thickness measurement. With the use of high resolution fabrication machines for micro/nano-electro-mechanical systems (MEMS/NEMS) such as Electron Beam Lithography (EBL), and Electron Beam Physical Vapor Deposition (EBPVD). Those fabrication technologies make it possible to further scale down the size of the Surface Acoustic Wave Devices (SAW) and specifically the Interdigital Transducers (IDTs) to hundreds nanometer. The maximum operation frequency of SAW resonators is limited by the width of IDTs and types of piezoelectric materials. Hence, hundreds nanometer size of IDTs will promote the operation frequency up to serval Gigahertz (GHz) which will improve the sensor device sensitivity. This is in contrast with previous implement processes of SAW resonators which depends on the available commercial integrated circuit (IC) fabrication processes, for example, the standard complementary metal oxide semiconductor (CMOS) technology. In this thesis, the design, simulation, and optimization of SAW resonators are introduced. We start the simulation using Commercial CMOSOL software from the simplest module that has single unit 2D module to verify that scaling down the size of the interdigital transducers (IDTs) can improve the resonate frequency. Then, build the single unit 3D module to measure the sensitivity. At last, we build the complete SAW resonator 3D module to run the simulation. To optimize the SAW resonator sensitivity performance, we simulate the device with several different piezoelectric materials including lithium niobate (LiNbO3), zinc oxide (ZnO), quartz (SiO2), aluminum nitride (AlN) and lead zirconate titanate (Pb(Zrx,Ti1-x)O3), or PZT-4). In addition, we adjusted the thickness of piezoelectric material layer to acquire higher resonator frequency. For higher amplitude, we change the distance between the IDTs and reflectors, and the height of the IDTs and the reflectors. All the simulations were done with 3D Finite Element analysis (FEA) on the COMSOL Multiphysics 5.2 platform, and the data results are processed in MATLAB.