Electrical measurement of undercut in surface micromachined structures

In a surface micromachined cantilever, the gap (g), beam thickness (t) and width get modified during fabrication. Since performance of sensors and actuators strongly depend on the final geometry, it becomes essential that these parameters are measured. Two sets of oxide anchored cantilever beams of different lengths with 20 and 30 mum widths are realised. On the released beams resonance frequency (f_i) measurements are performed. For a given length, by finding the ratio between measured frequencies for two widths, we get the value of undercut. Using this value in the slope of a f_i ² versus L^-4 plot we get the Young´s modulus (E) of beam material.