  Synchronous imaging is used in dynamic space-domain vibration profile studies
of capacitively driven, thin n+ doped poly-silicon microbridges oscillating at
rf frequencies. Fast and high-resolution actuation profile measurements of
micromachined resonators are useful when significant device nonlinearities are
present. For example, bridges under compressive stress near the critical Euler
value often reveal complex dynamics stemming from a state close to the onset of
buckling. This leads to enhanced sensitivity of the vibration modes to external
conditions, such as pressure, temperatures, and chemical composition, the
global behavior of which is conveniently evaluated using synchronous imaging
combined with spectral measurements. We performed an experimental study of the
effects of high drive amplitude and ambient pressure on the resonant vibration
profiles in electrically-driven microbridges near critical buckling. Numerical
analysis of electrostatically driven post-buckled microbridges supports the
richness of complex vibration dynamics that are possible in such
micro-electromechanical devices.
