High-Q, low impedance polysilicon resonators with 10 nm air gaps

This paper presents a fabrication process to manufacture air-gap capacitively-transduced RF MEMS resonators. 2-port measurements show motional impedance (R_x) < 1.3 k¿ and quality factor (Q) > 65,000 at 223 MHz in vacuum. The fabrication process involves depositing a dual-layer spacer of 10 nm of SiO₂ and 90 nm of hafnia via atomic layer deposition (ALD) followed by oxide release. Nanometer air gaps are achieved, while the hafnia provides reliability against shorting of resonator and electrode. Consistent performance was achieved across multiple devices, demonstrating the robustness of the process.