High-frequency lamb wave device composed of MEMS structure using LiNbO₃ thin film and air gap

Abstract

High-frequency devices operating at 3 GHz or higher are required, for instance, for future 4th generation mobile phone systems in Japan. Using a substrate with a high acoustic velocity is one method to realize a high-frequency acoustic or elastic device. A Lamb wave has a high velocity when the substrate thickness is thin. To realize a high-frequency device operating at 3 GHz or higher using a Lamb wave, a very thin (less than 0.5 μm thick) single-crystal plate must be used. It is difficult to fabricate such a very thin single crystal plate. The authors have attempted to use a c-axis orientated epitaxial LiNbO(3) thin film deposited by a chemical vapor deposition system (CVD) instead of using a thin LiNbO(3) single crystal plate. Lamb wave resonators composed of a interdigital transducer (IDT)/the LiNbO(3) film/air gap/base substrate structure like micro-electromechanical system (MEMS) transducers were fabricated. These resonators have shown a high frequency of 4.5 and 6.3 GHz, which correspond to very high acoustic velocities of 14,000 and 12,500 m/s, respectively, have excellent characteristics such as a ratio of resonant and antiresonant impedance of 52 and 38 dB and a wide band of 7.2% and 3.7%, respectively, and do not have spurious responses caused by the 0th modes of shear horizontal (SH(0)) and symmetric (S(0)) modes.

Design and Fabrication of S₀ Lamb-Wave Thin-Film Lithium Niobate Micromechanical Resonators

“…Many epitaxy growth methods [10]- [13] have been investigated for LN deposition. However high quality single crystal LN-film is yet to be demonstrated.…”

LiNbO3 thin film for A1 mode of Lamb wave resonators

“…1 and 2. The reason of the no spurious responses is because their thin LiNbO 3 films are composed of the twin epitaxial crystalline one 7, 8. It is consisted that the response at around 4.7 GHz in Fig.…”

“…Authors realized good c‐orientated LiNbO 3 twinned crystalline epitaxial films by a chemical vapor deposition (CVD) and applied them to 4.5 and 6.3 GHz (at resonant frequency ( f r )) Lamb wave resonators on their thin LiNbO 3 films 7, 8. In their papers, the 4.5 GHz resonator showed a large impedance ratio of 52 dB at resonant ( f r ) and anti resonant frequencies ( f a ) but the 6.3 GHz one did not a large impedance ratio as 38 dB.…”

S0 Mode Lamb Wave Resonators Using LiNbO3 Thin Plate on Acoustic Multilayer Reflector

“…Surface acoustic wave (SAW) [1][2][3][4][5][6] and bulk acoustic wave (BAW) [7][8][9][10][11] devices have been widely used for such systems. In recent years, high-frequency, such as 4.5-6.2 GHz, antisymmetric A 1 mode Lamb wave resonators [12][13][14][15] have been reported, and are considered for application to future highfrequency mobile systems. These four reports showed characteristics of the membrane-type (MEMS type) A 1 mode Lamb wave resonators using thin LiNbO 3 plates or films.…”