A novel technique for extraction of material properties through measurement of pull-in voltage and off-capacitance of beams

The mechanical properties of the structural layer play important role in the design and optimization of MEMS structures. The pull-in measurement is a popular technique used to measure the mechanical properties of a material, but its success depends on the accurate measurement of the gap (g) between the beam and the ground plane and its uniformity. In this paper we propose a novel technique which does not require accurate knowledge of the value of 'g'. In our proposed method, a large number of beams with different lengths (L) are to be fabricated simultaneously and the off-Capacitance (Coff) in addition to pull-in voltage (Vpi) measured in the same set-up. This is followed by a plot of (Coff3Vpi2L4 / A3) vs (1/A) for beams under bending dominating condition and (Coff3Vpi2L2 /A3) vs (1/A) for beams under stress dominating condition, where A is the area of a beam. The plots are extrapolated to intersect the y-axis. The value of the intercept can be used to extract the values of Young's modulus and residual stress, without any definite knowledge of the value of 'g'. In this paper, we have shown with the help of simulations that using our method the material properties can be extracted very accurately even when the gap (g) is very nonuniform.