Active reflectors for high performance lithium niobate on silicon dioxide resonators

This paper reports on the design and demonstration of active reflectors for enhancing the electromechanical coupling (k_t²) and suppressing spurious modes in Laterally Vibrating Resonators (LVRs) based on X-cut ion-sliced Lithium Niobate (LN) thin film on silicon dioxide (SiO₂). By adding electroded quarter wavelength (λ/4) regions at the two ends of the resonant plate, active reflectors (since an electrical signal is applied to them) are formed to improve the device performance. Optimized active reflectors that resort to 100% metal coverage of the λ/4 extensions enable: (i) a considerable improvement of k_t², (ii) spurious mode suppression, and robustness to processing (iii) misalignment and (iv) over/under-etching. 2X improvement in k_t² and significant suppression of in-band spurious vibrations were attained with respect to the conventional design (without active reflectors) despite 0.5 μm misalignment and more than 0.5 μm overetch in the fabrication process.