High Q Lateral-Field-Excited Bulk Resonator Based on Single-Crystal LiTaO₃ for 5G Wireless Communication

The paper presents the design and fabrication of lateral-field-excited (LFE) resonators based on 42° Y-cut single-crystal LiTaO
₃
(LT) on silicon dioxide (SiO
₂
). A simple coplanar top electrode is defined to excite the bulk acoustic wave modes in the suspended LT/SiO
₂
structure, and the fabrication process that only involves two lithography steps is more simplified compared to that of commercial film bulk acoustic wave resonators. For a model structure consisting of LT(670 nm)/SiO
₂
(1500 nm) thin film, two types of acoustic modes are both piezoelectrically active in the LT film: the first one is the thickness-shear mode with a resonance frequency of 2.46 GHz, an electromechanical coupling (
$k_{eff}^{2}$
) of 1.4%, a high quality factor (
${Q}$
) of 1690, and the second one corresponds to longitudinal mode with a resonance frequency of 4.39 GHz,
${k} _{eff}^{2}$
of 1.2%, a high
${Q}$
of 1590, which is among the highest reported for piezoelectric MEMS resonators operating at this frequency range. The excellent performance would enable application scenarios including high-resolution sensors, low-phase-noise oscillators, and low-loss, high selectivity filters in the sub-6 GHz range for the fifth-generation (5G) wireless communication.