On the electrical characterization of carbon overcoats

Carbon overcoat has been used extensively on both disks and heads to enhance the tribological properties of head/disk interfaces. The electric properties, such as resistivity and breakdown voltage of the carbon overcoat are of great interest with the advent of magneto-resistance technology. The characterization and the underlying mechanisms of these electric properties will be extensively discussed. A highly reproducible computer-controlled voltage-current (V-I) setup, on carbon and ZrO₂ overcoats ranging from 100 to 250 Å in thickness, is used to measure resistance and breakdown voltage. An analytic model, based on the thermal and electrical properties of the carbon overcoat was used to interpret data. Basically, the model states that the increasing voltage causes thermal heating in the overcoat, thereby lowering its resistivity. Yet, when the applied field is sufficiently large, heating becomes excessive and thermal run-away occurs, resulting in the breakdown of the carbon. The model achieved good agreement with experimental results and its implication is discussed