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

• Published in: ACS applied materials & interfaces Vol. 6; no. 12; pp. 9376 - 9385
• Main Authors: Yeo, Reuben J, Dwivedi, Neeraj, Rismani, Ehsan, Satyanarayana, Nalam, Kundu, Shreya, Goohpattader, Partho S, Tan, H. R, Srinivasan, Narasimhan, Druz, Boris, Tripathy, S, Bhatia, C. S
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 25.06.2014
• Subjects: carbon overcoat; silicon nitride; corrosion protection; surface modification; head−disk interface
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am501760p

An ultrathin bilayer overcoat of silicon nitride and carbon (SiN x /C) providing low friction, high wear resistance, and high corrosion resistance is proposed for future generation hard disk media. The 16 Å thick SiN x /C overcoat consists of an atomically thin SiN x underlayer (4 Å) and a carbon layer (12 Å), fabricated by reactive magnetron sputtering and filtered cathodic vacuum arc (FCVA), respectively. When compared with monolithic overcoats of FCVA-deposited carbon (16 Å) and sputtered SiN x (16 Å), the SiN x /C bilayer overcoat demonstrated the best tribological performance with a coefficient of friction < 0.2. Despite showing marginally less electrochemical corrosion protection than monolithic SiN x , its ability to protect the magnetic media from corrosion/oxidation was better than that of an ∼27 Å thick commercial hard disk overcoat and 16 Å thick monolithic FCVA-deposited carbon. From X-ray photoelectron spectroscopy and Raman spectroscopy analyses, it was found that the introduction of the 4 Å SiN x underlayer facilitated higher sp3 hybridization within the carbon layer by acting as a barrier and promoted the formation of strong bonds at the SiN x /C and the SiN x /media interfaces by acting as an adhesion layer. The higher sp3 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).