Super-High-Frequency Low-Loss Sezawa Mode SAW Devices in a GaN/SiC Platform

Area of Science:

• Materials Science
• Electrical Engineering
• Microelectromechanical Systems (MEMS)

Background:

• Traditional epitaxial Gallium Nitride (GaN) technology often involves thick buffer layers, limiting frequency scaling in surface acoustic wave (SAW) devices.
• Sezawa mode operation in SAW devices offers potential for higher frequencies but is constrained by material and fabrication limitations.

Purpose of the Study:

• To investigate the performance of Sezawa mode surface acoustic wave (SAW) devices fabricated on an ultrathin GaN/SiC platform.
• To achieve record high frequencies for GaN-based microelectromechanical systems (MEMS) by eliminating buffer layers.
• To correlate simulated and measured device performance metrics.

Main Methods:

• Utilized Finite Element Analysis (FEA) to determine the frequency range for Sezawa mode support.
• Designed, fabricated, and characterized transmission lines and resonance cavities with interdigital transducers (IDTs).
• Developed modified Mason circuit models for performance metric extraction and correlated with measured phase velocity and piezoelectric coupling.

Main Results:

• Achieved Sezawa mode operation at frequencies exceeding 14 GHz, a first for GaN/SiC platforms.
• Demonstrated a maximum piezoelectric coupling coefficient (k^2) of 0.61% and a frequency-quality factor product (f·Qm) of 6x10^12 s^-1 for resonators at 11 GHz.
• Observed minimum propagation loss of 0.26 dB/λ for two-port devices and confirmed strong correlation between simulated and measured dispersion.

Conclusions:

• Eliminating buffer layers in GaN/SiC platforms is crucial for enabling high-frequency Sezawa mode SAW devices.
• The study demonstrates a viable pathway for developing next-generation high-frequency GaN MEMS.
• The achieved performance metrics represent a significant advancement in GaN-based acoustic wave device technology.