Overview of corrosion on thin film magnetic media & its implication on head disk interface

Oxidation products of cobalt and nickel are formed on the overcoat surface when thin film disks are exposed to corrosive environments and high humidity. Evidences have shown the localized corrosion is caused by incomplete coverage of the thin films. Pores with openings on the surface serve as conduits for corrosive agents' attack of the underlying metal. Cobalt corrosion occurs primarily along texture line due to less than perfect coverage of carhon overcoat on sharp topographic features. Nickel corrosion results from deep pinholes in the carbon and metal films reaching to NiP substrate. The adsorbed water and pinholes in the films enable the galvanic interaction between the electrically conductive carbon and the underlying metal films, namely, corrosion. The corrosion products will accumulate on the air-bearing surface during head sweeping and degrade the read-back amplitude. Reducing pinhole in the films and utilizing resistive carbon overcoat are effective in improving corrosion resistance on thin film disks. Several component level corrosion tests have been developing for pinhole decoration. Hence, process conditions can be optimized to minimize the corrosion susceptibility of thin film disks.