Abstract
In this work, three-dimensional finite element analysis (3D FEA) of quasi-surface acoustic wave (QSAW) resonators with high accuracy is reported. The QSAW resonators consist of simple molybdenum (Mo) interdigitated transducers (IDT) on solidly mounted stacked layers of AlN/Mo/Si. Different to the SAW resonators operating in the piezoelectric substrates, the reported resonators are operating in the QSAW mode, since the IDT-excited Rayleigh waves not only propagate in the thin piezoelectric layer of AlN, but also penetrate the Si substrate. Compared with the commonly used two-dimensional (2D) FEA approach, the 3D FEA method reported in this work shows high accuracy, in terms of the resonant frequency, temperature coefficient of frequency (), effective coupling coefficient () and frequency response. The fabricated QSAW resonator has demonstrated a of 0.291%, series resonant frequency of 422.50 MHz, and of −23.418 ppm/°C in the temperature range between 30 °C and 150 °C, for the design of wavelength at 10.4 m. The measurement results agree well with the simulations. Moreover, the QSAW resonators are more mechanically robust than lamb wave devices and can be integrated with silicon-based film bulk acoustic resonator (FBAR) devices to offer multi-frequency function in a single chip.
Highlights
Scattering (S) parameters of the fabricated quasi-surface acoustic wave (QSAW) resonators are characterized by a Keysight vector network analyzer in air with an open chamber probe station at room temperature
To validate the accuracy of the 3D finite element analysis (FEA) method, the QSAW resonators with λ of 10.4 μm, 10 μm, 9.6 μm and 9.2 μm are designed, fabricated and characterized
aluminum nitride (AlN)/Mo/Si layers with split Mo interdigitated transducers (IDT) fingers laid on the surface
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. SAW devices are usually fabricated based on lithium niobate (LiNbO3 ) piezoelectric substrate and have demonstrated excellent performance of high-quality factor (Q) as well as large effective coupling coefficient [5,6,7,8]. The AlN thin-film-based SAW resonator is more likely to be a kind of quasi-SAW (QSAW) device. Twodimensional (2D) FEA is a typical method to investigate and design SAW transducers and resonators, which provides a simple and quick way for SAW device simulations [14,15,16,17]. To verify the accuracy of the 3D FEA approach, key parameters for designing QSAW resonators such as frequency, admittance response, k2e f f and temperature coefficient of frequency (TCF) are investigated and discussed in both simulation and experiment
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