Imaging MEMS Motion at Nano Scale by Time-Resolved Scanning Electron Microscopy*

Reconfigurable micro-optics and on-chip integrated photonics often rely on micro-opto-electro-mechanical-systems to provide dynamical optical processing such as beam steering and focusing or optical coupling and phase tuning. In the process of design and fabrication of micro-electro-mechanical-systems (MEMS), and to assess their quality, a local and direct measurement of their motion on a point-by-point basis is quite useful. Such a technique must be fast enough to track the MEMS dynamics with sub-micron resolution. We introduce and discuss an implementation of dynamical imaging of MEMS by time-resolved scanning electron microscopy (SEM). MEMS resonators are actuated close to their resonance frequencies, and we show how to obtain stroboscopic movies by a proper sequential acquisition of secondary electron signal. Unprecedented information about local trajectory is provided, in the microsecond scale and at tens of nanometer lateral scale. In-operando nonlinearities in the response of the system, interpretable as related to system hardening are brought into evidence. We also discuss strategies to reach the ultrafast time scale.