Micromachined piezoelectric Lamb wave resonators: a review

With the development of next-generation wireless communication and sensing technologies, there is an increasing demand for high-performance and miniaturized resonators. Micromachined piezoelectric Lamb wave resonators are becoming promising candidates because of their multiple vibration modes, lithographically defined frequencies, and small footprint. In the past two decades, micromachined piezoelectric Lamb wave resonators based on various piezoelectric materials and structures have achieved considerable progress in performance and applications. This review focuses on the state-of-the-art Lamb wave resonators based on aluminum nitride (AlN), aluminum scandium nitride (Al x Sc1−x N), and lithium niobate (LiNbO3), as well as their applications and further developments. The promises and challenges of micromachined piezoelectric Lamb wave resonators are also discussed. It is promising for micromachined piezoelectric Lamb wave resonators to achieve higher resonant frequencies and performance through advanced fabrication technologies and new structures, the integration of multifrequency devices with radio frequency (RF) electronics as well as new applications through utilizing nonlinearity and spurious modes. However, several challenges, including degenerated electrical and thermal properties of nanometer-scale electrodes, accurate control of film thickness, high thin film stress, and a trade-off between electromechanical coupling efficiencies and resonant frequencies, may limit the commercialization of micromachined piezoelectric Lamb wave resonators and thus need further investigation. Potential mitigations to these challenges are also discussed in detail in this review. Through further painstaking research and development, micromachined piezoelectric Lamb wave resonators may become one of the strongest candidates in the commercial market of RF and sensing applications.