Laterally Excited Bulk Acoustic Wave Resonators with Rotated Electrodes Using X-Cut LiNbO₃ Thin-Film Substrates

Area of Science:

• Materials Science
• Electrical Engineering
• Acoustics

Background:

• Piezoelectric-on-insulator (POI) substrates enable X-cut LiNbO3 thin-film resonators with tunable resonant frequency (f) and effective electromechanical coupling coefficient (Keff2).
• These resonators are crucial for applications requiring adjustable frequency and strong electromechanical interaction.

Purpose of the Study:

• To investigate the impact of electrode angle rotation (θ) on laterally excited bulk acoustic wave resonators.
• To analyze the effects of θ on acoustic wave modes, resonant frequency (f), and effective electromechanical coupling coefficient (Keff2).
• To provide insights for designing multi-band and multi-bandwidth filters using X-cut LiNbO3 thin-film resonators.

Main Methods:

• Simulations and experimental measurements of resonators fabricated on X-cut LiNbO3/SiO2/Si substrates.
• Analysis of resonators with and without cavities, focusing on electrode angle rotation (θ).
• Characterization of acoustic wave modes, including longitudinal leaky SAWs (LLSAWs), shear horizontal SAWs (SH0-SAWs), lateral vibrating resonators (LVRs), and plate wave resonators (PAWs).

Main Results:

• Electrode angle rotation (θ) induces distinct electric field directions, leading to changes in acoustic wave modes.
• Resonators without cavities exhibited LLSAW (θ=0°) and SH0-SAW (θ=90°) modes with Keff2 values of 1.62% and 26.6%, respectively.
• Resonators with cavities showed S0 LVR (θ=0°) and SH0-PAW (θ=90°) modes with higher Keff2 values of 4.82% and 27.66%, respectively, along with improved Q factors.

Conclusions:

• Electrode angle rotation is a critical parameter for controlling the performance of X-cut LiNbO3 thin-film resonators.
• The study demonstrates significant variations in Keff2 and Q-factor based on the resonator type and electrode orientation.
• Findings offer a pathway for developing advanced filters with tailored multi-band and multi-bandwidth characteristics.