  Graphene flake-based dispersions are attractive materials for various
applications in microelectronics because of their ease of fabrication and the
potential to deposit them on diverse substrates. The integration of these
materials into conductive networks and microdevices requires thorough knowledge
of their mechanical material properties, including adhesion. This paper
presents quantitative adhesion measurements of graphene flake networks on
silicon dioxide (SiO${_2}$) via button shear testing (BST). In this method,
shear forces are applied to prefabricated micrometric buttons until they
delaminate, providing information about the shear strength of the underlying
graphene. We applied BST to graphene flake networks with different flake
structures and defect densities. Flat flakes, a flat network structure, and a
high flake defect density improve adhesion. We further demonstrate that
graphene flake networks have stronger adhesion than chemical vapor deposited
monolayer graphene grown on copper and transferred to SiO${_2}$.
Hexamethyldisilazane (HMDS) increases the total adhesion force by improving
flake network formation. Finally, we provide flake-type-specific delamination
patterns by combining BST, optical microscopy, and Raman spectroscopy. We
establish BST as a quantitative technique for measuring the adhesion of
graphene dispersions and show the crucial role of interflake junctions in the
overall adhesion of graphene flake networks.
