On-chip integrated 0.4 GHz & 2.3 GHz Lamb wave resonators: Electrode structure optimization and flip-transfer fabrication

—Lamb wave resonators show great potential for applications in RF filters, infrared detectors, and sensors. Converting the bottom electrode into an interdigitated-transducer (IDT) structure allows broader application. However, the piezoelectric film deposited atop patterned IDTs often suffers from poor quality and cracking, degrading or damaging resonator performance. This study presents a wafer-level flip-transfer method which flips the pre-defined piezoelectric vibration and cavity structures onto another wafer. This reversed the sequence of bottom electrode patterning and piezoelectric film deposition, avoiding the problem above. Utilizing this process, Lamb wave resonators operating at 0.4 GHz and 2.3 GHz with both IDT-IDT and IDT-Floating configurations were integrated on an 8-inch wafer. Furthermore, electrode parameters were optimized to enable the multi-mode coupling and suppress spurious signals. Test results indicate that, with 9.5 % Sc doping, Lamb wave resonators operating in the 0.4 GHz and 2.3 GHz bands achieved effective electromechanical coupling coefficients (k_t²) of 2.87 % and 6.24 %, and quality factors (Q) of 2547 and 1332, respectively.