Coverage and properties of a-SiNx hard disk overcoat

Amorphous silicon nitride (a-SiNx) overcoats are deposited on magnetic disks by rf-reactive sputtering to study their coverage and properties. According to the x-ray photoelectron spectroscopy analysis, a-SiNx has a low coverage-limit of ∼10 A compared with that of the reference a-CNx (∼20 A). The lower coverage-limit of a-SiNx may be attributed to its high density of 3.2 g/cm3, which corresponds to 93% bulk density. By contrast, the density of diamond-like carbon is only 54% that of diamond. This is in agreement with the results of coverage simulation, which reveal that the film coverage thickness decreases by ∼3 A per 10% increase in the relative density. Compared with 45 A a-CNx coated disks, 15 A a-SiNx coated disks have fewer pinhole defects and are more durable in the accelerated flyability test. The superior performance of a-SiNx disk overcoat may be attributed to its dense structure and high hardness (25 GPa).