Development and implementation of automated interferometric microscope for study of MEMS inertial sensors

Marinis, Ryan Thomas

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Development and implementation of automated interferometric microscope for study of MEMS inertial sensors

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Microelectromechanical systems (MEMS) are quickly becoming ubiquitous in commercial and military applications. As the use of such devices increases their reliability becomes of great importance. Although there has been significant research in the areas of MEMS errors, there is a lack of work regarding long term reliability of packaged systems. Residual thermomechanical stresses might relax over time which affects physical distances within a package, ultimately influencing the performance of a device. One reason that there has not been sufficient work performed on the long-term effects on structures might be the lack of a tool capable of characterizing the effects. MEMS devices have been measured for shape and its changes using interferometric techniques for some time now. Commercially available systems are able to make high resolution measurements, however they might lack loading options. To study aging effects on components a test might need to run continuously for days or weeks, with systematic operations performed throughout the process. Such a procedure is conducive to an automated data acquisition system. A system has been developed at WPI using a Twyman-Green interferometer and a custom software suite. The abilities of this system are demonstrated through analysis performed on MEMS tuning fork gyroscope (TFG) sensors. Specifically, shape is recorded to investigate die bond relaxation as a function of time and thermal cycle. Also presented are measurements made using stroboscopic illumination on operating gyroscopes, in situ. The effect of temperature on the performance of the sensors is investigated using a customized precision rate table.

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