Measurement and testing of microstructure dynamics is necessary to develop reliable and marketable microelectromechanical system (MEMS) products. However, it is not easy to test MEMS dynamic behavior because of its micro structure, high frequency response upon excitation and complex operation environment. We have investigated the optical methods potentially suitable for MEMS dynamics characterization, and developed a measurement system for surface topography, three-dimensional motions, and modal parameters of MEMS.
Several key techniques have been integrated in the measurement system such as phase shifting interferometry (PSI), micro vision, and stroboscopic illumination. A base excitation subsystem and an environmental control facility have also been included, enabling base excitation under variable pressure and/or temperature for MEMS testing. A new spin filter algorithm has been introduced to effectively reduce noise for the measured fringe patterns without influencing the 2π jumps in the wrapped phase maps. A novel hybrid block matching algorithm has also been proposed to extract the in-plane displacement from vision images with a sub-pixel resolution.
A lot of experimental investigations have been carried out on several typical MEMS devices such as micro gyroscopes, micro mirrors, pressure sensor membranes, atomic force microscope (AFM) cantilevers, and micro resonator arrays. The investigations have confirmed that such a measurement system is able to measure the surface topography and deformations as well as the in- plane and out-of-plane motions of microstructures, and is effective and efficient to characterize MEMS dynamics with a nanometer resolution. A vertical scanning white light interferometer has been added in the latest version of the system, and it enables the system to measure surface profile with a much larger range.
Fig. 1. Layout of the measurement system for MEMS Dynamics Characterization
Fig. 2. Measured amplitude frequency response of an AFM cantilever showing its resonant frequency of 13.03kHz
Fig. 3. Measured vibration of the AFM cantilever within an excitation cycle of 80μs under different driven voltages
Fig. 4. Measured deformation of a pressure sensor membrane under different pressures of 0.1Mpa and 0.5Mpa.
Fig. 5. Latest version of the measurement system with a vertical scanning white light interferometer
