Density dependence of the electrochemical characteristics of carbon overcoated thin film media

Abstract

The effectiveness of carbon overcoats as a corrosion barrier for thin film media has been studied. The sputtering pressure and power used during the deposition of the carbon overcoat has a direct influence on its density, and thus upon its corrosion protection characteristics for the underlying metal media. Corrosion rates of the carbon overcoated metal media were measured both electrochemically and by exposing disks to conditions of elevated temperature and humidity. Corrosion measurements show that the corrosion rate of the magnetic media, (sputtered at a constant pressure and power), increases with increased deposition pressure (1–30 mTorr) and decreased sputtering power (2.8–0.3 kW) of the carbon film. The increased corrosion rate is caused by a decrease in density of the carbon film. In another experiment, sputtering pressure was varied in both the magnetic and overcoat layers. Corrosion measurements reveal a relatively small change in corrosion rate for sputtering pressure in the range of 1 to 6 mTorr of Ar, but a significant increase at 30 mTorr. This sharp increase was attributed to an increase in surface area of the magnetic layer believed to be generated by the the formation of rough porous films at high pressure. In this study carbon and magnetic films sputtered at high power and low pressure yield media with the lowest corrosion rate.

Cobalt Oxide Diffusion Kinetics in Ultra-Thin Amorphous Carbon Films

“…These tests typically expose the disks to elevated temperatures, humidity, and/or acid environments as a function of time and of carbon overcoat film thickness and quantify the Co oxide evolution by various metrology. Increases in the carbon film density and/or changes to their composition often allow improved corrosion protection at reduced overcoat film thicknesses [3][4][5][6].…”