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Single-digit-nanometer electrode-to-resonator gaps have enabled 200-MHz radial-contour mode polysilicon disk resonators with motional resistance Rx as low as 144W 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. 

An on-chip strain measurement device is demonstrated that harnesses precision frequency measurement to precisely extract sub-nm displacements, allowing it to determine the residual strain in a given structural film with bestin-class accuracy, where stress as small as 15MPa corresponds to 2.9nm of displacement. The approach specifically harnesses a spoke-supported ring structure (cf. Fig. 1) surrounded both inside and outside by balanced capacitivegap transducers that pull its resonance frequency according to strain-induced changes in inner and outer electrode-tostructure gap spacing. The use of a ring structure with balanced electrodes further eliminates uncertainty in the starting gap spacing, which in turn enhances accuracy. The importance of attaining such accuracy manifests in the fact that knowledge of residual strain might be the single most important constraint on the complexity of large mechanical circuits, such as the mechanical filter of [1].