Toughness Measurement of Microscale Coating/Silicon MEMS System Using Pillar Splitting Method

This work innovatively employed the pillar splitting method to extract the fracture toughness of silicon microstructures with full coating of diamond like carbon (DLC) introduced by plasma-enhanced chemical vapor deposition (PECVD). The DLC coating with different hardness and elastic modulus by adjusting the deposition bias voltage at -200 and -600 V was grown on bare silicon pillars with diameters of 5, 8, and
$10~\mu $
m. We established a
$\gamma $
selection method specifically tailored for laminated composite structures. The discontinuity observed in the force-displacement curve in pillar splitting was reported, in which the interrelationship between fracture toughness, crack nucleation, and propagation in the pillar splitting was analyzed. Both types of coatings significantly improved the fracture toughness of the pillar microstructure compared to uncoated samples, with the fracture toughness monotonically increasing with the coating hardness, which was confirmed by finite element simulations, exhibiting similar trends as the pillar splitting experiments. This work validates the feasibility of using the pillar splitting method for fracture toughness characterization of coating/substrate microsystems and can be applied to fracture behavior testing of other composite structures.