Nanomechanical Spectroscopy of Ultrathin Silicon Nitride Suspended Membranes

TL;DR

This study investigates the mechanical properties of ultrathin silicon nitride suspended membranes using AFM-based nanomechanical spectroscopy, revealing higher elastic modulus and reduced stress post-fabrication, with models for elastic modulus and capillary forces.

Contribution

It provides new measurements of elastic modulus and stress in ultrathin silicon nitride membranes and introduces a mathematical model for normalized elastic modulus and capillary force effects.

Findings

Elastic modulus of suspended membranes is higher than on substrate.

Net stress decreases after membrane suspension.

Capillary forces can cause membrane collapse.

Abstract

Mechanical properties of a nanomechanical resonator have a significant impact on the performance of a resonant Nano-electromechanical system (NEMS) device. Here we study the mechanical properties of suspended membranes fabricated out of low-pressure chemical vapor deposited silicon nitride thin films. Doubly-clamped membranes of silicon nitride with thickness less than 50 nm and length varying from 5 um to 60 um were fabricated. The elastic modulus and stress in the suspended membranes were measured using Atomic Force Microscope (AFM)-based nanomechanical spectroscopy. The elastic modulus of the suspended membranes was found to be significantly higher than those of corresponding thin films on the substrate. A reduction in the net stress after the fabrication of suspended membrane was observed and is explained by estimating the contributions of thermal stress and intrinsic stress. We establish a mathematical model to calculate the normalized elastic modulus of a suspended membrane. Lastly, we study the capillary force-gradient between the SiNx suspended membrane-Si substrate that could collapse the suspended membrane.