Enabling Higher Order Lamb Wave Acoustic Devices With Complementarily Oriented Piezoelectric Thin Films

• Published in: Journal of microelectromechanical systems Vol. 29; no. 5; pp. 1332 - 1346
• Main Authors: Lu, Ruochen, Yang, Yansong, Link, Steffen, Gong, Songbin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 5G mobile communication; 5G new radio; Acoustic coupling; acoustic delay lines; Acoustic devices; acoustic resonators; Acoustics; Broadband; Delay lines; Insertion loss; lamb wave; Lamb waves; Lithium niobate; Lithium niobates; piezoelectric devices; Piezoelectricity; Q factors; Radio frequency; Resonance; Resonators; RF microsystems; Stress; Thin films; thin-film devices
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2020.3007590

In this work, we present a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films. Acoustic characteristics are first theoretically explored with COP lithium niobate (LiNbO 3 ) thin films, showing their excellent frequency scalability, low loss, and high electromechanical coupling (<inline-formula> <tex-math notation="LaTeX">k^{2} </tex-math></inline-formula>). Acoustic resonators and delay lines are then designed and implemented, targeting efficient excitation of higher-order Lamb waves with record-breaking low loss. The fabricated resonator shows a <inline-formula> <tex-math notation="LaTeX">2^{\mathbf {nd}} </tex-math></inline-formula>-order symmetric (S2) resonance at 3.05 GHz with a high quality factor (<inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula>) of 657, and a large <inline-formula> <tex-math notation="LaTeX">k^{2} </tex-math></inline-formula> of 21.5% and a <inline-formula> <tex-math notation="LaTeX">6^{\mathbf {th}} </tex-math></inline-formula>-order symmetric (S6) resonance at 9.05 GHz with a high <inline-formula> <tex-math notation="LaTeX">Q </tex-math></inline-formula> of 636 and a <inline-formula> <tex-math notation="LaTeX">k^{2} </tex-math></inline-formula> of 3.71%, both among the highest demonstrated for higher-order Lamb wave devices. The delay lines show an average insertion loss (IL) of 7.5 dB and the lowest reported propagation loss of 0.014 dB/<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> at 4.4 GHz for S2. Notable acoustic passbands up to 15.1 GHz are identified. Upon further optimizations, the proposed COP platform can lead to gigahertz low-loss wideband acoustic components. [2020-0127]