Modeling and design of discrete track recording media

In this paper, modeling and design of discrete track recording (DTR) media are done. The DTR media consists of lands on which the data is stored and recessed grooves that provide the magnetic isolation between adjacent data tracks. A simple model is formulated which assumes writing occurs over the land as well as the entire groove, with only a degradation due to the spacing loss in the groove. To account for this spacing loss, measurements are made on disks with different overcoats and an empirical expression for the spacing dependence is derived. The total spacing loss included the normal -55 d/λ dB "Wallace" read spacing loss as well as the empirically derived write spacing loss expression. The maximum signal level from the grooves or adjacent lands is required to be 30 dB lower than for the signal on the land being read. A plot of groove depth requirements is done for different areal densities for given magnetic read widths. As these read widths become larger, a greater portion of the read sensor would detect transitions in the groove, and thus the groove depth must become larger. For the 120 Gb/in₂ design, a filling factor of 2/3 translates to a groove width of 65 nm. Widening the magnetic read width to half the track pitch would require a groove depth of 26 nm, a value 2.5 times smaller than the width. For filling factors 0.6 and 0.7, there is a 1 dB improvement in media signal-to-noise ratio (SNR) for modest groove width-depth ratios of 3, over a conventional flat disk.