Characterization of MEMS cantilevers using lensless digital holographic microscope

Abstract

In this paper vibration characterization of MEMS cantilevers are presented using lens-less in-line digital holographic microscope (LDHM). In-line digital holography provides larger information capability with higher phase sensitivity, and full CCD sensor area is utilized for real image reconstruction. In lensless in-line digital holographic microscope, a highly diverging beam replaces the conventional microscope objectives to provide the required magnification. The diverging wave geometry also reduces the effect of twin-image wave caused by the in-line holographic geometry. For vibration analysis, the time averaged holograms were recorded corresponding to different vibration states of the cantilevers. Direct numerical evaluation of the amplitude and phase information from single time averaged hologram provides the full-field real time quantitative analysis. The experimental study of vibration measurements of Aluminum nitride (AlN) driven cantilevers is performed. The full field study shows the simultaneous vibration behavior of many cantilevers corresponding to same input conditions. Our study shows the shift in the resonant condition of cantilevers both for first and second resonant frequencies. This kind of analysis is most suitable to optimize and monitoring the fabrication process of cantilevers.