Single-Digit-Nanometer Capacitive-Gap Transduced Micromechanical Disk Resonators

Single-digit-nanometer electrode-to-resonator gaps have enabled 200-MHz radial-contour mode polysilicon disk resonators with motional resistance Rx as low as 144 while still posting Q’s exceeding 10,000, all with only 2.5V dc-bias. The demonstrated gap spacings down to 7.98nm are the smallest to date for upper-VHF micromechanical resonators and fully capitalize on the fourth power dependence of motional resistance on gap spacing. High device yield and ease of measurement debunk popular prognosticated pitfalls often associated with tiny gaps, e.g., tunneling, Casimir forces, low yield, none of which appear. The devices, however, are more susceptible to environmental contamination when unpackaged. The tiny motional resistance, together with (Cx/Co)’s up to 1% at 4.7V dc-bias and (Cx/Co)-Q products exceeding 100, propel polysilicon capacitive-gap transduced resonator technology to the forefront of MEMS resonator applications that put a premium on noise performance, such as radar oscillators.