Quality Factor Degradation Due to the In-plane Misorientation in POI-SAW Resonators

In this work, shear horizontal surface acoustic wave (SH-SAW) resonators with tiny misorientation on Piezo-On-Insulator (POI) substrates were studied. POI-SAW resonators with different in-plane orientations were simulated by 3-D finite element analysis (FEA). The results show that the mechanical loss of POI-SAW resonators will increase significantly when the in-plane orientation is deviated from the crystallographic axis with in-plane symmetry due to additional scattering. Subsequently, ultra-thin 42° Y-X LiTaO
3
(LT) films on low-loss layered supporting substrates (SiO
2
/sapphire, SiO
2
/poly-Si/Si, and SiO
2
/quartz) with precise bonding alignment were selected to verify this conclusion, and the SH-SAW resonators with different in-plane orientations on the above POI substrates were fabricated and measured. The measured results exhibit that the
$Q_{\max}$
(maximum Bode-Q) decreases from 3898 to 819 when the deviation angle θ=3°. The Q
p
(
$Q$
value at the anti-resonance frequency) attenuation of the SH-SAW resonators on these substrates exceeds 50% when θ> 2°. Even a slight misorientation can cause a dramatically degraded
$Q$
value, indicating that the misalignment during the wafer bonding and lithography process will result in unwanted
$Q$
degradation, and eliminating the potential misorientation is one of the keys to achieving high-
$Q$
SAW devices.