Optical interferometric displacement calibration and thermomechanical noise detection in bulk focused ion beam-fabricated nanoelectromechanical systems

Abstract

Optical interferometric techniques are used for absolute (calibrated) displacement measurements of focused ion beam (FIB)-fabricated nanoelectromechanical systems (NEMS). FIB nanomachining of bulk Si gives rapidly prototyped cantilever and doubly clamped beam devices. Ion impingement from orthogonal directions allows tailoring of deep, undercut-free gaps between the device layer and the bulk, in turn allowing large amplitude NEMS oscillatory motion, access to a nonlinear readout regime and a new calibration method for optical interferometric displacement detection. The measurements are sensitive enough to determine the thermomechanical noise floor of a bulk FIBed NEMS device with a displacement sensitivity of 166 fm Hz−½, limited by the combination of optical shot noise and detector dark current. This sensitivity, comparable to the state of the art for free-space optical interferometry of NEMS, validates the robustness of the bulk FIB fabrication technique for rapid prototyping of nanoscale mechanical devices.