18 February 2008 Electrical measurement of undercut in surface micromachining
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Abstract
In a surface micromachined cantilever the beam thickness, width and the gap get modified during fabrication. Since performance of sensors and actuators strongly depend on the final geometry, it is essential to measure these parameters. Electrical measurements have several advantages over microscopy and we present here two different electrical techniques to measure undercut due to etching. In the resistance based approach, two polysilicon resistors of different length and width are used and the undercut is extracted from the ratio of the measured resistances. In the second technique, resonance frequency is measured for two sets of oxide anchored polysilicon cantilever beams with 20 and 30 µm widths. For a given length, the ratio between the measured frequencies for the two widths gives the value of undercut. Measurements are done on both wet and dry etched polysilicon.
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Somashekara Bhat, Somashekara Bhat, Enakshi Bhattacharya, Enakshi Bhattacharya, } "Electrical measurement of undercut in surface micromachining", Proc. SPIE 6884, Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VII, 68840R (18 February 2008); doi: 10.1117/12.764417; https://doi.org/10.1117/12.764417
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