OUT OF PLANE FLEXURAL BEHAVIOUR OF THIN POLYSILICON FILMS: MECHANICAL CHARACTERIZATION AND APPLICATION OF THE WEIBULL APPROACH

A new MEMS for on-chip mechanical testing of 0.7 µm thick polysilicon film has been designed, modelled and fabricated. The polysilicon film is electrostatically loaded under bending until rupture in the out of plane direction, by means of electrostatic attraction in the direction orthogonal to the substrate. This is at difference with previous works of the same Authors, in which results relevant to in plane loading conditions have been presented. 3D Finite Element (FE) and Boundary Element (BE) models of the structure were used during the design and data reduction phases. Tests were carried out at room temperature and at atmospheric humidity. The measured Young’s modulus obtained on 20 tested polysilicon specimens was 174 ± 9 GPa. Rupture stress computed after 21 tests, treated with the Weibull statistical theory, gave Weibull material parameters σ0 = 2237 MPa, with a Weibull modulus m = 5.1