Wave Propagation Direction and c-Axis Tilt Angle Influence on the Performance of ScAlN/Sapphire-Based SAW Devices

Area of Science:

• Materials Science
• Acoustics
• Thin Film Technology

Background:

• Surface Acoustic Wave (SAW) devices traditionally use bulk piezoelectric substrates.
• Natural Single-Phase Unidirectional Transducers (NSPUDTs) exhibit directional acoustic power radiation based on crystal orientation.
• Previous NSPUDT research focused on bulk substrates.

Purpose of the Study:

• To investigate acoustic wave directionality in thin film SAW devices.
• To explore directionality in c-axis tilted scandium-doped aluminum nitride (ScAlN) films on sapphire.
• To analyze the influence of c-axis tilt and propagation direction on Sezawa mode performance.

Main Methods:

• Fabrication of c-axis tilted ScAlN thin films (up to 5.5° tilt) on sapphire substrates.
• Utilizing split finger electrodes for measuring forward and backward insertion loss.
• Evaluating return loss and insertion loss across various SAW propagation directions and tilt angles.
• Comparing performance between Rayleigh and Sezawa acoustic modes.

Main Results:

• Observed acoustic wave directionality in c-axis tilted ScAlN thin film SAW devices.
• Directionality was specifically noted in the Sezawa mode.
• Performance metrics (insertion loss, return loss) were correlated with c-axis tilt angle and wave propagation direction.

Conclusions:

• C-axis tilted ScAlN thin films enable acoustic wave directionality in SAW devices, particularly in the Sezawa mode.
• This finding extends the concept of NSPUDTs to thin film technologies.
• The study provides valuable data on optimizing ScAlN SAW device performance through controlled c-axis tilt and propagation direction.