A Wafer-Level Vacuum-Packaged Vertical Resonant Electric Field Microsensor

This article presents a wafer-level vacuum packaged vertical resonant electric field microsensor (EFM), which uses an anodic bonded glass in silicon, silicon on insulator, and glass on silicon (GIS-SOI-GOS) triple-stack structure. GIS is innovatively employed to fabricate the external driving electrode, which is used to vertically drive the resonator at the device layer of SOI. SOI is used to fabricate the sensing structure. GOS is used to establish the electric field induction channel. A theoretical model is established to characterize the output characteristics of the novel EFM. Numerical simulations are conducted to optimize the key structural parameters. The fabrication process based on bulk micromachining is employed to manufacture the microsensor. The developed EFM is characterized experimentally. The experimental results show that the air pressure in the vacuum chamber is about 5 Pa, and a driving voltage of 7 V dc and 0.07 V-p ac is needed to realize the vertical resonance of the sensing structure. The microsensor demonstrates a sensitivity of 0.31 mV/(kV/m) with a linearity of 5.84% within the electric field range of 0-50 kV/m, which further improves the sensitivity of the wafer-level vacuum-packaged EFM.