P.W. Nutter

An investigation of the effects of media characteristics on read channel performance for patterned media storage

Many view data storage on patterned magnetic media as one way of attaining storage densities in excess of 1 Tb/in/sup 2/ and thus overcoming the problems associated with recording at ultrahigh densities on conventional continuous media. In this paper we investigate, through the use of a replay simulation developed to take into account the three-dimensional nature of the patterned media, the effects that the shape-constrained media have on the bit-error-rate performance of the read channel in 1-Tb/in/sup 2/ perpendicular recording. In particular, we analyze how media configurations with varying island shape, size, and distribution affect the channel performance.

Effect of island distribution on error rate performance in patterned media

The size, shape, and distribution of islands in a patterned medium depends on the patterning process adopted. The off-track performance in this case is mainly dominated by inter-track interference due to the neighboring islands. In this paper, the effect that the island distribution has on the off-track performance is investigated with respect to read channel bit-error-rate performance.

Effect of island geometry on the replay signal in patterned media storage

In a move to extend the storage capabilities of magnetic storage systems beyond 1 Tb/in/sup 2/, the use of patterned media has often been cited. Here, recorded domains are constrained by the geometry of the magnetic island and not the geometry of the recording head. Conventional two-dimensional readout modeling techniques, using the reciprocity integral, rely on the assumption that the across-track medium magnetization is uniform under the giant magnetoresistive replay head. However, in the case of a geometrically constrained medium this is not the case. This work investigates the effect that the island geometry has on the characteristics of the replay signal in perpendicular patterned magnetic media storage through the extension of the reciprocity integral to three dimensions. The paper describes replay pulses that offer different characteristics from those obtained by conventional two-dimensional techniques. The origins of these differences are explained by the variation in medium magnetization across the track.

Understanding Sources of Errors in Bit-Patterned Media to Improve Read Channel Performance

The limitations of current lithographic techniques result in a variation of the geometry of the fabricated islands in bit-patterned media. These variations give rise to jitter in the replay waveform that has a detrimental effect on the recovery of stored data. By analyzing experimental bit-patterned media, we show that the presence of lithography jitter can be quantified in terms of variations in the size and position of the islands, which can be seen to be Gaussian-like in nature. In addition, the amount of jitter increases as the periodicity and size of the islands reduces, confirming that lithography jitter will be a significant source of noise in any future storage system incorporating bit-patterned media. By using a comprehensive read channel model we demonstrate that a novel trellis structure offers improved read channel performance in the presence of island position variations.

Spatial sensitivity mapping of Hall crosses using patterned magnetic nanostructures

Obtaining an accurate profile of the spatial sensitivity of Hall cross structures is crucial if such devices are to be used to analyze the switching behavior of magnetic nanostructures and determine the switching field distribution of bit patterned media. Here, we have used the anomalous Hall effect to investigate the switching of patterned Co/Pt multilayer magnetic nanoislands, where the Hall cross has been integrated into the Pt seed layer. Using the anomalous Hall output voltage we have observed the magnetic switching of individual islands, allowing the spatial sensitivity across a Hall cross structure to be determined. The experimental results agree well with numerical simulation studies, using a three-dimensional finite element model, and with existing theoretical studies, where the spatial sensitivity of two-dimensional Hall cross structures have been found numerically.

High resolution magnetic force microscopy study of e-beam lithography patterned Co∕Pt nanodots

E-beam lithography has been used to pattern a continuous Co∕Pt multilayer film with perpendicular anisotropy into circular islands of various sizes down to 25nm diameter on a 60nm pitch. High resolution magnetic force microscopy with in situ applied field has been used to directly determine the switching field distribution (SFD) and hysteresis loop of the islands. For the smallest islands, the coercivity is reduced and the width of the SFD is increased, indicating that they would not be well suited to data storage applications.

Improved Data Recovery from Patterned Media With Inherent Jitter Noise Using Low-Density Parity-Check Codes

Patterned magnetic media promises areal densities in excess of 1 Tbit/in2 for data storage. However, current imperfect patterning techniques result in a variation in the dimensions and distribution of the fabricated islands. As a result, this variation introduces jitter in the replay waveform that makes data recovery difficult. In this paper, we investigate the use of low-density parity-check (LDPC) codes and iterative decoding for mitigating the effects of lithography jitter and improving the read channel performance in patterned media storage systems. In addition, we show that the adoption of LDPC coding techniques permits an increase in the data storage capability of the medium to approximately 1.6 Tbit/in2 with acceptable bit-error-rate performance.

Temperature Dependent Remanence Loops of Ion-Milled Bit Patterned Media

Magnetic multilayered thin films with perpendicular anisotropy have been patterned into nanoscale islands by ion-milling with an oxygen-plasma patterned carbon hard mask. The islands have been studied by scanning electron microscopy (SEM) and magnetic force microscopy (MFM) to determine the switching field distribution and its origin. Larger islands exhibit coercivities of ~ 450 kA/m (5.6 kOe), but coercivity falls rapidly when island diameter falls below 40 nm. The switching field distribution becomes larger in absolute terms and as a fraction of the coercivity as island diameter falls. The origin of these effects is thought to be edge damage during ion milling and intrinsic defects (grain boundaries or dislocations) in the original magnetic thin film.

Humanoid Upper Torso Complexity for Displaying Gestures

Body language is an important part of human-to-human communication; therefore body language in humanoid robots is very important for successful communication and social interaction with humans. The number of degrees of freedom (d.o.f) necessary to achieve realistic body language in robots has been investigated. Using animation, three robots were simulated performing body language gestures; the complex model was given 25 d.o.f, the simplified model 18 d.o.f and the basic model 10 d.o.f. A subjective survey was created online using these animations, to obtain peoples opinions on the realism of the gestures and to see if they could recognise the emotions portrayed. It was concluded that the basic system was the least realistic, complex system the most realistic, and the simplified system was only slightly less realistic than the human. Modular robotic joints were then fabricated so that the gestures could be implemented experimentally. The experimental results demonstrate that through simplification of the ...

Partial Response Maximum Likelihood for Optical Data Storage Using Simple Optical Equalizers

The effects of introducing shading bands into the collector path of optical storage devices to equalize optically the signal to a partial response target have been investigated. A software simulation of the optical readout process and the partial-response maximum-likelihood (PRML) read channel have been developed and used to evaluate different channel configurations. It is shown that optical filtering can be used to eliminate the requirement for digital filtering in the PRML channel.