Determination of the modification of Young's modulus due to Joule heating of polysilicon microstructures using U-shaped beams

The modification of Young's modulus is determined before and after Joule heating generated by a current passing through polysilicon microstructures. U-shaped overhanging polysilicon beams are specially designed and fabricated to avoid both the heat transfer to substrate and the deformation by thermal expansion. Joule heating is performed by applying a current of 10-20 mA for 5-10 s, making beams heat up. The measured resonant frequencies shift up or down after Joule heating, attributed to the stress relaxation or the oxidation of beams. The modification of Young's modulus is negligible, implying that material properties after the reshaping are not changed much.