Dynamical topography measurements of MEMS up to 25 MHz, through transparent window, and in liquid by Digital Holographic Microscope (DHM)

DHMs have unique features especially relevant for MEMS characterization. They provide 3D topography for large vertical ranges with interferometric resolution, in a single acquisition, without any lateral or vertical scanning. Any standard microscopic objective can be mounted on them, including those with correction for cover glass thickness. In this paper, DHM is operated in conjunction with a laser pulsed stroboscopic module providing synchronization of camera acquisition and shutter, laser pulses with length down to 7.5 ns, and MEMS excitation signal up to 25 MHz. These systems can measure fast movements over large vertical amplitude, in- and out-of-plane motions of device with complex geometry, provide a statistical analysis of multiple single devices, and can measure under vacuum or in liquid and/or through transparent window. This is illustrated with the presentation of the measurements of a cantilever, an ultrasonic transducer, a variable capacitor, and a gyroscope.