On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

TL;DR

This study employs bulge testing to accurately measure the mechanical properties, including Poisson's ratio, of ultra-thin Si3N4 and Si3N4/SiO2 membranes, providing results consistent with existing literature.

Contribution

It introduces a method to determine Poisson's ratio of submicron thick membranes using bulge tests with various membrane geometries.

Findings

Measured Poisson's ratio for Si3N4 membranes is 0.29.

Determined residual stress and Young's modulus consistent with literature.

Validated bulge test as effective for ultra-thin membrane characterization.

Abstract

In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\pm$ 14 GPa, s0 = 420 $\pm$ 8 and u = 0.29.