A resonant method for determining mechanical properties of Si3N4 and SiO2 thin films

This study investigates the measurement of Poisson's ratio and Young's modulus of silicon dioxide (SiO2) and silicon nitride (Si3N4) thin films using a resonant method. Two thin films, which are SiO2 and Si3N4, are fabricated as the specimens of microcantilever beams and plates using the bulk micromachining. The resonant frequency of the cantilever beams and plates is measured using a laser interferometer. The Young's modulus of thin films can be calculated from the resonant frequency of the cantilever beams, and the Poisson's ratio of thin films is determined by the frequency of the cantilever plates. Experimental results show that the Poisson's ratios of SiO2 and Si3N4 are 0.16 and 0.26, respectively, and the Young's moduli of SiO2 and Si3N4 are, respectively, 55.6 GPa and 131.6 GPa.