Today's magnetic thin film disks support a continually increasing areal density and provide a very durable interface necessary for low flying across the disk surface. In addition, this surface must be very smooth with essentially no defects to minimize contacts with the slider, and exhibit minimal waviness which could also interfere with low flying. Disks are formed by the process of sputtering multiple metallic films and a protective overcoat layer onto a highly planar, low defect glass substrate. At Hitachi Global Storage Technologies, Inc., glass has been chosen based on its smoothness as well as modulus which yields stable mechanical properties in the drive. The protective overcoat which is normally a carbon based material, is covered with a thin lubricant layer to improve the durability of the head disk interface. To avoid head stiction, Hitachi employs a ramp load/unload mechanism which prevents the head from resting on the disk when it is not rotating. This allows the use of very smooth disk surfaces and facilitates the continuing trend to lower flying.

To support high density recording, the magnetic media must be very thin with small grain size, yet have high magnetization and a high coercivity. Areal density of the recording media in disk drive products is now increasing at a 100 % compound annual growth rate which involves a corresponding small bit cell sizes. Since the signal to noise ratio is proportional the number of magnetic particles per bit to the one-half power, progressively smaller grains with a higher disk coercivity are required with every generation of disk drive. The spacing laws require a progressively decreasing magnetic spacing between the head and disk as areal density increases. This involves the head flying closer to the disk, as well as using a thinner protective overcoat while maintaining a highly durable interface.

As bit cell sizes decreases, the energy required to reverse the magnetization of a bit approaches the magnitude of the bit's thermal energy, causing a magnetic instability. This behavior is called superparamagnetism and relates to the future extendibility of magnetic storage. Proper selection of disk materials and structures can significantly delay the superparamagnetic effect.

The future development of both the magnetic media films and overcoats for next generation of disk drive products requires technical innovations in magnetic materials, new disk structures, sputter deposition and tooling, advanced magnetic measurements and testing.

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