High-density perpendicular recording-advances, issues, and extensibility

Longitudinal recording is approaching its areal density limits, and consequently the compound areal growth rate of areal density on hard disk drives has recently been slowing. A transition to perpendicular recording is expected somewhere above 100 Gbit/in2. In this paper, the advantages of perpendicular recording over longitudinal recording are briefly summarized and the issues that must be overcome for perpendicular recording to become both successful and extensible are discussed. A key advantage of perpendicular recording is improved writability, which is due to a number of factors, including excellent anisotropy orientation, optimized write field angle, and the use of a soft magnetic underlayer to enhance the write fields. Obtaining an optimized design requires small grain size, large anisotropy field and large effective write fields, just as in longitudinal recording. On the other hand, the use of the soft underlayer brings with it some problems. DC fields from tracks neighboring the one being written or read can affect both the write and read processes. Although areal density is found to be relatively insensitive to bit aspect ratio, it is quite sensitive to the “soft erase” width, the distance that must be allowed between the writer pole edge, and the adjacent track to ensure that repeated writing on a track does not cause thermal demagnetization of previously written bits on an adjacent track. This brings the necessity to confine the write fields in the cross-track direction using shields or some other means. Finally, although at low densities it may be possible to use trapezoidal poles to reduce the effects of head skew on areal density, at high areal densities, other means must be found.