Ultralow Acoustic Loss Micromachined Butterfly Lamb Wave Resonators on AlN Plates

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 67; no. 3; pp. 671 - 674
• Main Authors: Zou, J., Gao, A., Pisano, Albert P.
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.03.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic loss; Acoustic resonance; Acoustics; Aluminum nitride; Frequency control; III-V semiconductor materials; Impedance; Lamb wave resonator (LWR); Lamb waves; Micromachining; Q factors; quality factor; Resistance; Resonance; Resonators; Rewiring
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2019.2945235

This study reports the design of a novel Butterfly Lamb wave resonator (LWR) employing the S 0 mode in the AlN plate, and for the first time, its ultrahigh parallel-resonance quality factor (Q p ) of 4,021 is demonstrated, indicating an ultralow acoustic loss. Although the series resonance quality factor (Q s ) is widely used for various loss comparisons, it is inconclusive since Q s is always dominated by the routing resistance (Rs), which is normally huge without the thick metal rewiring. Instead, Q p is a precise representation of the acoustic loss level for its independence of R s and as it is closer to Q max of the Bode Q-curve in the IDT-excited devices. A butterfly-shaped resonance cavity, theoretically predicted to reduce the anchor loss and suppress the transverse spurious mode, has been applied to the AlN LWR and experimentally shown to boost the Q p by 2.3 times. In addition, a directly measured Bode-Q curve for the LWR is reported for the first time, showing superior Q profile for the Butterfly-LWR than the conventional-LWR and good agreement with the 3 dB- Q p 's.