Mechanical Mode Coupled Piezo-on-Silicon Bulk Acoustic Wave MEMS Resonators in Tank Configuration for Q-Enhancement

A low-cost, commercially fabricated thin-film piezoelectric-on-silicon (TPoS) MEMS resonator demonstrating high quality factor (Q) and low motional resistance (Rm) is presented. A mechanically coupled tank topology is employed, coupling a fully differential central TPoS resonator with multiple non-electroded single-crystal silicon (SCS) disks. Three variants of this topology have been designed and validated experimentally, exploiting extensional and in-plane shear modes. The button-like (BL) mode forms the central TPoS tank, to which four breathing (BR) or wineglass (WG) mode disks are appended, resulting in configurations denoted BL-4BR and BL-4WG, respectively. A third variant, BL-12WG, utilizes twelve appended wineglass disks. In moderate vacuum (90 mTorr), the BL-12WG configuration achieves an exceptionally high unloaded quality factor (Qul) of 55,000 and an Rm of 347 , representing approximately an 11-fold increase in Qul and a 2.4-fold reduction in Rm compared to an uncoupled BL resonator. The WG mode, in particular, exhibits enhancement factors nearly proportional to the number of appended SCS disks. Key design considerations-including mechanical dynamics, mode selection, and simulated performance-are discussed. The BL- 12WG resonator, with its superior performance, emerges as a strong candidate for low-phase-noise oscillators.