Practical Measurements of Stiffness, Displacement, and Comb Drive Force of MEMS

We present the first practical measurements of stiffness and comb drive force of a micro electro mechanical system (MEMS). Compared to previous efforts, our method is easier to implement, faster to perform, and lower in cost. Our method provides direct quantification of the uncertainty of a single measurement. Our method is amenable to automated industrial-level batch probing or on-chip post-packaged measurements. In this paper, we test our method with using several MEMS on difference dies that were fabricated in the standard SOIMUMPs foundry process. Our planar geometry measurements compare favorably to optical and electron microscopy, with an uncertainty on the order of nanometers. Our measurements of comb drive force are a function of voltage and capacitance only and are thusly traceable. With our current test bed, our uncertainty in force is on the order of nanonewtons with lots of room for improvement. Our measurement of stiffness is obtained from our measurements of force and deflection. We also discuss the theory of our methodology.