High-crystallinity 30% scaln enabling high figure of merit x-band microacoustic resonators for mid-band 6g

This paper presents an experimental comparison of high-performance X-band piezoelectric 30% Sc-doped Aluminum Nitride (ScAlN) Cross-sectional Lame Mode resonators (CLMRs) for two different thin-film's crystallinity levels. The presented MEMS devices stand out in terms of electromechanical coupling (k(t)(2)) and quality factor (Q) in this frequency range, while being fabricated with a low-complexity 3-masks micro-machining process. Nevertheless, the resonators employing a higher crystallinity film feature motional Q . k(t)(2) Figures of Merit (FoM) that are up to 5.6 times higher per same geometry, highlighting the impact of the piezoelectric layer quality in the final device performance. Moreover, motional quality factors (Q(m)) larger than similar X-band AlN devices are achieved while attaining a 6-fold increase in k(t)(2). This demonstrates that ScAlN can deliver resonator performance well beyond the one achievable by AlN ones and, more importantly, that the doping process does not degrade the mechanical properties of microelectromechanical devices, provided that a high-quality piezoelectric film is used. This work features a motional Q . k(t)(2) Figure of Merit of 73 at 9.5 GHz, being, to the authors' knowledge, the highest ever shown above 8 GHz and a bank of lithographically frequency-definable resonators with record-breaking metrics covering the 8 to 11 GHz range, all fabricated on the same substrate. Such metrics have the power of enabling the synthesis of compact, wide-bandwidth, and low insertion loss passive pass-band filters for the next generation 5G and 6G cellular radios.