Button Shear Testing for Adhesion Measurements of 2D Materials

TL;DR

This paper introduces and validates a button shear testing method to quantitatively measure the adhesion strength of various 2D materials on different substrates, aiding reliable device integration.

Contribution

It presents a novel, reliable testing technique for measuring 2D material adhesion, including fabrication process details and the effects of substrate treatments.

Findings

Low substrate roughness enhances adhesion.

Oxygen plasma treatment increases shear strength.

Thermal annealing improves hBN adhesion.

Abstract

Two-dimensional (2D) materials are considered for numerous applications in microelectronics, although several challenges remain when integrating them into functional devices. Weak adhesion is one of them, caused by their chemical inertness. Quantifying the adhesion of 2D materials on three-dimensional surfaces is, therefore, an essential step toward reliable 2D device integration. To this end, button shear testing is proposed and demonstrated as a method for evaluating the adhesion of 2D materials with the examples of graphene and hexagonal boron nitride (hBN), molybdenum disulfide, and tungsten diselenide on silicon dioxide (SiO${_2}$) and silicon nitride substrates. We propose a fabrication process flow for polymer buttons on the 2D materials and establish suitable button dimensions and testing shear speeds. We show with our quantitative data that low substrate roughness and oxygen plasma treatments on the substrates before 2D material transfer result in higher shear strengths. Thermal annealing increases the adhesion of hBN on SiO${_2}$ and correlates with the thermal interface resistance between these materials. This establishes button shear testing as a reliable and repeatable method for quantifying adhesion of 2D materials.