Enhanced Tribological, Corrosion, and Microstructural Properties of an Ultrathin (<2 nm) Silicon Nitride/Carbon Bilayer Overcoat for High Density Magnetic Storage

An ultrathin bilayer overcoat of silicon nitride and carbon (SiNx/C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 angstrom thick SiNx/C overcoat consists of an atomically thin SiNx underlayer (4 angstrom) and a carbon layer (12 angstrom), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 angstrom) and sputtered SiNx (16 angstrom), the SiNx/C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiNx, its ability to protect the magnetic media from corrosion/oxidation was better than that of an,similar to 27 angstrom thick commercial hard disk overcoat and 16 angstrom thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 angstrom SiNx underlayer facilitated higher sp(3) hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiNx/C and the SiNx/media interfaces by acting as an adhesion layer. The higher sp(3) carbon content is expected to improve the thermal stability of the overcoat, which is extremely important for future hard disk drives employing heat assisted magnetic recording (HAMR).