High-Performance SAW Resonator With Simplified LiTaO₃/SiO₂ Double Layer Structure on Si Substrate

Area of Science:

• Materials Science
• Electrical Engineering
• Acoustics

Background:

• Increasing mobile data traffic necessitates advanced radio frequency (RF) band filters with superior low-loss and steep frequency characteristics.
• High-quality (Q)-factor and low-temperature coefficient of frequency (TCF) resonators are crucial for meeting these demands.
• Previous work showed a three-layer surface acoustic wave (SAW) resonator on LiTaO3 (LT) achieved higher Q-factors than standard 42° rotated YX-LT (42YX-LT) substrates.

Purpose of the Study:

• To investigate a simplified layer structure for SAW resonators to enhance performance.
• To optimize the two-layer structure for improved Q-factor, TCF, and electromechanical coupling coefficient (k²).
• To evaluate the practical application of the optimized structure in RF filters.

Main Methods:

• Investigated a two-layer structure by removing the AlN layer from a previously studied three-layer SAW resonator.
• Employed finite element method (FEM) for numerical analysis to understand acoustic wave energy confinement and optimize layer thicknesses.
• Fabricated and evaluated prototype one-port resonators at frequencies ranging from 0.95 to 3.6 GHz.

Main Results:

• The two-layer structure achieved a 3 to 4 times higher Q-factor compared to standard 42YX-LT SAW resonators.
• Optimizing layer thicknesses improved TCF and electromechanical coupling coefficient (k²).
• A 2.4-GHz band Wi-Fi filter utilizing the two-layer structure demonstrated low-loss, improved steepness, and high attenuation.

Conclusions:

• A simplified two-layer SAW resonator structure offers significant Q-factor enhancement without performance degradation.
• This structure provides a pathway to reduced complexity in RF filter fabrication.
• The developed two-layer structure is suitable for high-performance RF filters in applications like Wi-Fi.