Characterization of static and dynamic optical actuation of Al microbeams by microscopic interferometry techniques

Out-of-plane optical actuation of thin Al cantilever microbeams was investigated as a function of laser beam power, spot size, modulation frequency and location on the beam. Several microscopic interferometry techniques including quantitative time-averaged interferometry and phase shifting stroboscopic interferometry were used to determine the resonant frequencies, vibration mode shapes and optically induced mean deflection of the microbeams. Transient response measurements by stroboscopic interferometry are also demonstrated. Experimental results show that on-wafer, non-contact, full-field dynamic measurements can be performed up to at least several hundred kHz although a large light power is necessary to actuate Al microbeams. It is demonstrated that dynamical optical actuation tends to saturate as a function of laser beam power and is maximum when the laser spot is located below 1/3 of the beam length. It is also evidenced that fundamental resonant frequencies measured with optical actuation are lower than that measured with piezoelectric actuation. Results are discussed by considering that actuation is dominated by photothermal effects.