Surface Acoustic Wave (SAW) resonators have been widely used in wireless communication below 2 GHz. However, as wireless communication evolves into 5G and 6G, with the new frequency bands above 3 GHz and bandwidth exceeding 500 MHz, conventional SAW technology face serious bottlenecks in terms of high frequency (>3GHz), high quality factor (Q value), and high electromechanical coupling coefficient (k 2 ).
The main limitation of traditional SAW technology is that it has been using single piezoelectric coefficient to achieve the conversion between electrical and mechanical energy. To solve the issue, a research team led by Prof. ZUO Chengjie from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) developed a Coupled Shear SAW (CS-SAW) resonator that utilizes two coupling coefficients of different directions (e 16 and e 34 ). Their work was published in IEEE Electron Device Letters .
The team designed and prepared the CS-SAW resonator based on a LiNbO 3 -on-SiC (LNoSiC) substrate. By selecting the proper three-dimensional (3D) Euler angle (α) and designing the thickness (h LN ) to wavelength (λ) ratio of the LiNbO 3 thin film, the horizontal and vertical electric fields simultaneously excite two piezoelectric coefficients (e 16 and e 34 ), making them coherently coupled in one single vibration pattern. Results showed that this CS-SAW resonator achieved an unprecedented high k 2 of 34% at 5 GHz and an excellent figure of merit (FoM) up to 221. Compared to all reported SAW resonators above 4 GHz in the recent ten years, the team’s CS-SAW resonator working at 5 GHz and 6 GHz have the highest FoM.
This work explored the possibility of coupling two or more piezoelectric coefficients in single vibration pattern and designed a criterion for realizing such coupled shear modes, opening up a new research path for acoustics devices such as wideband filters, tunable resonators, highly sensitive sensors and so on.
IEEE Electron Device Letters
Coupled Shear SAW Resonator With High Electromechanical Coupling Coefficient of 34% Using X-Cut LiNbO₃-on-SiC Substrate
22-Feb-2024