Adam F. Torabi

One terabit per square inch perpendicular recording conceptual design

Analysis based on the use of a high-gradient shielded pole write head indicates that a one terabit per square inch perpendicular recording system can be realized. System features include the following: BPI/TPI=7; H/sub k/=21 kOe; 4/spl pi/M/sub s/=7 kg; weak exchange coupling to cancel self demagnization; 20 grains per bit cell; side shields on writer; and low-skew writing.

Write performance of shielded pole heads on media with thin soft underlayers

Nonlinear finite element calculations show that the soft underlayer thickness in perpendicular media can be greatly reduced without significant loss of effective switching field strength by using a shielded pole writer in place of the more conventional monopole geometry. In addition, use of a thin soft underlayer (SUL) with a shielded pole writer with a thin SUL results in a higher gradient and a narrower magnetic write width. These results have been qualitatively confirmed experimentally.

Measurement of transition shape, width, and total magnetic spacing

Measurement of the harmonics of low-frequency all-ones patterns and the shield-to-shield read gap are used here to reconstruct the spacing, the isolated transition shape, and the width parameter for longitudinal recording. For perpendicular, the media thickness parameters and data at two spacings are needed to accurately determine the spacing and width parameter. The -90% to +90% transition shapes fits well to a tanh(x/a) shape for longitudinal and perpendicular recording.

Front-end write process model for high data rate longitudinal magnetic recording

In drive designs with write data rates >1 Gb/s, transitions sent to the write head collide at 1T with reflections from earlier transitions. This increases the need for write-driver voltage headroom, efficient interconnects, and efficient magnetic materials. Design alternative studies in this regime require detailed models of all components in the write process. We modeled nonlinear bit transition shift (NLTS) and spectral signal-to-noise ratio (SNR) measurements using our preamp/interconnect/writer/media model and compared it to measurements of the actual devices that were modeled. We describe methods for reconciling write driver models with varying head and interconnect impedance, verification performed with scanning Kerr effect microscopy (SKEM), and magnetic models with instantaneous nonlinear effects included.

Performance evaluation of different pole geometries in thin film heads

To achieve higher areal density, inductive thin film recording heads require smaller track pitch. Pole trimming of conventional heads where P1 width is made equal to the P2 width is suggested in literature as a method for increasing the track density. A patented design called the bevel head where pole P1 of the conventional head is beveled to have the same width as P2 width at the gap, is shown to have equivalent offtrack performance as the pole trimmed heads. The bevel heads require a simpler process to manufacture compared to the pole trimmed heads. Three dimensional field maps are computed for conventional heads, pole trimmed heads and for the beveled heads at different values of write currents. Using these field maps, a simulation of the recording process is done to compute the erase width, write width, read width and isolated pulse response. Both pole trimmed heads and the bevel heads show improvement over the conventional heads in accomplishing a narrower erase width. An offtrack capability model is developed to fit the experimental 747 curve based on the microtrack profile, erase width and a SNR value. Using this model, track density is calculated for all the three heads. Pole trimmed heads and bevel heads show a similar improvement over conventional heads in accomplishing higher track density. >

Gap dependence of the shielded pole heads

The shielded pole writer improves the write field gradient of a perpendicular write pole by placing a shield close to it on the down stream side. It also improves writability by enhancing the longitudinal component of the field and thus providing more tipping field, which reduces the Stoner-Wolfarth switching threshold. However the flux leakage from the write pole to the shield causes saturation to occur sooner and thus reduces the maximum field strength available. Therefore there is a trade-off to be made between the gain in gradient and the loss in field as the gap is reduced. These results are supported by a large statistics experiment in which the write gaps of 50, 75, and 200 nm were investigated.