Research on functionally divided protective overcoat films for improving tribological characteristics of magnetic disks

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The purpose of this research is to reduce magnetic head wear in hard disk drives to realize contact recording systems to improve information recording density. For this purpose, a new concept of functionally divided protective overcoat films was proposed and the methods to produce the film were investigated. In functionally divided protective overcoat films, the carbon overcoat film on a magnetic disk was divided into two films. Lower layer is devoted for corrosion resistance and wear durability with high hardness, while the upper layer reduces friction between head and disk and head wear with low hardness asperities. With this functionally division, we expected high performance protective overcoat films on magnetic disks.However, it is not common to produce island type carbon film on flat carbon film. The search for the production methods was very difficult. Finally, we have found that the filtered cathodic arc (FCA) deposition method would successfully produce desired films. Nitrogenated FCA carbon films with asperities less than 10 nm height were shown to be able to reduce pin wear in pin-on-disk type wear test. This proved that functionally divided protective overcoat films are possible.This concept would increase the height of asperities and it was considered to be a broblem for lower head disk spacing. Then, disk burnishing techniques to disk asperity heights were studied parallel to the above. The effect of burnishing conditions on head wear were investigated and showed that both conventional tape burnishing and newly proposed contact burnishing with diamond burnishing sliders were effective in reducing head wear.In addition to above, the effects of disk lubricant on head wear were also studied. It was shown that the higher the morecular weight of a lubricant the lower the head wear and phosphazene type functional end group was more effective in reducing head wear than hydroxyl end groups was.