Strength and Fracture Resistance of Amorphous Diamond-Like Carbon Films for MEMS

Abstract EN

The mechanical strength and mixed mode I/II fracture toughness of hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C) films, grown by pulsed laser deposition, are discussed in connection to material flaws and its microstructure.

The failure properties of ta-C were obtained from films with thicknesses 0.5–3 μm and specimen widths 10–20 μm.

The smallest test samples with 10 μm gage section averaged a strength of 7.3 ± 1.2 GPa, while the strength of 20-μm specimens with thicknesses 0.5–3 μm varied between 2.2–5.7 GPa.

The scaling of the mechanical strength with specimen thickness and dimensions was owed to deposition-induced surface flaws, and, only in the smallest specimens, RIE patterning generated specimen sidewall flaws.

The mode I fracture toughness of ta-C films is KIc=4.4±0.4 MPam, while the results from mixed mode I/II fracture experiments with cracks arbitrarily oriented in the plane of the film compared very well with theoretical predictions.