Microelectromechanical systems (MEMS) are typically fabricated out of materials that are mechanically sound at the microscale, but can be relatively poor electrical conductors. For this reason, areas of MEMS can be coated with various thin metal films to provide electrical pathways. These films, however, may drastically alter mechanical properties of the device. In this paper we investigate how metallization of microcantilevers affects the quality factors, (Q). Using two sets of silicon microcantilevers that are coated with aluminium films from 5 nm to 30 nm thick, on one side and two sides, respectively, the Q-factors are experimentally determined using the ring-down method. The ring-down method entails mechanically exciting the microcantilevers at their fundamental resonance frequency, abruptly stopping the excitation, and then measuring the decay of oscillation amplitude as a function of time. From this ring-down curve, the Q-factor of each microcantilever can be determined. Results show that the greater the thickness of the aluminium film, the lower the Q-factor will be. We also show a significant temperature dependency of the Q-factor of aluminium coated microcantilevers.
In this paper, we describe confocal optoelectronic holography microscopy (COEHM) technique specifically being developed for characterizing the shape of MEMS and microelectronics. This is particularly important because shape is directly related to the functionality, performance, and integrity of the microstructures of interest. A specific feature of COEHM is that it allows characterization of high aspect ratio MEMS and microelectronics. Representative applications demonstrating the capabilities of COEHM are presented. It is shown that measurement resolution is highly dependent on the numerical aperture (NA) of the optical components comprising COEHM and on the quality of image digitization.By utilizing optical components characterized by a magnification factor of 50x and a NA of 0.45, measurement resolution of 25 nm is achieved. The resolution can he increased to 8 nm when utilizing optical components characterized by a magnification factor of l0Ox and a NA of 0.73.
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