Heating effects on the Young's modulus of films sputtered onto micromachined resonators

Surface-micromachined polysilicon lateral resonant structures were fabricated and used to determine the temperature dependence of the Young's modulus of the polysilicon. This is done by passing a de current through the beams during resonance testing, resulting in Joule-heating. The temperatures are calibrated by increasing the de current until the melting point of silicon is attained. The calculated Young's moduli agree well with reported values for single crystal silicon. In addition, metal films were sputter-deposited onto the polysilicon resonators, and similar experiments performed on the composite devices to determine the temperature dependence of the modulus of the sputtered films. Ni films demonstrate a linear decrease in Young's modulus with temperature. TiNi films demonstrate two distinct modulus values with an intermediate transition region, due to the temperature-induced reversible phase transformation exhibited by TiNi.