Fig. 2: Device visualization by SEM and 3D laser scanning confocal microscope.
From: Highly-sensitive wafer-scale transfer-free graphene MEMS condenser microphones
a SEM false color image of one final device (geom. C) in tilted view and low-magnification mode. Partial Cr/Au cracks are present on top of the multi-layer graphene tethers due to thermal stress experienced during the Cr/Au evaporation. A slower evaporation rate is found to improve the reported state. Undesired mask shift during the back-alignment step in hard contact resulted in misalignment and the unintended closure of venting holes. b Optical microscope image of the same device as in (a). c Laser topography image of the same device as in (a). d, e Optical microscope, and topography images of a collapsed device. As inset in (c, e), a height scale is added showing a downward deformation of the poly-Si back-plate due to thermal stress of ≈1.5% (center) of the suspended region. The main source of the compressive stress can be a residual thin layer of TEOS
