Analysis of Data Recovery Techniques for use with Patterned Media Storage

EPSRC funded project GR/R63479/01, Sept. 2002 - Sept. 2005, £68,019.

Manchester staff/students involved:

• Dr Paul W Nutter (PI)
• Prof Barry K Middleton (CoI)
• Dr David McA. McKirdy
• Ioannis Ntokas (PhD Student)

With grateful help from:

• Dr Mohammed Zaki Ahmed (University of Plymouth)
• Dr Hazel Shute (University of Plymouth)
• Dr David Wilton (University of Plymouth)
• Cen J. Tjhai (PhD student, University of Plymouth)

Overview

The continued demand for increased storage densities has resulted in unprecedented storage capabilities in today's magnetic hard disc drives. Key to the evolution of magnetic storage has been the continued development and refinement of the recording media and the read/write head. The current belief is that even following the impending move to perpendicular media, which will offer increased storage capacity, current continuous thin film media will be unable to support storage densities in excess of 1Tbit/in² due to the advent of thermal stability problems. The use of patterned media is hailed by many as being one approach to overcome the physical limitations of current continuous media and their development as viable storage media is receiving considerable interest in both academia and the storage industry.

The thrust of this project was to investigate the implications of discrete media upon the data recovery process, through extensive simulation and analysis, for use in magnetic storage systems incorporating patterned media with perpendicular anisotropy.

The overall purpose of this project was to investigate the issue of data recovery from patterned media storage systems. In particular three objectives were identified:

• Investigation of the readout process in patternd media storage systems
• Investigation of data recovery in patterned media storage systems
• Fabrication of sample patterned media

Outcomes

Significant outcomes of this research that will be used to determine which technologies are used in patterned media are summarised briefly below.

1. The demonstration that 3D reciprocity-based magnetic replay models are essential in order to take into account the 3D nature of the storage medium and the read head and thus accurately design and analyse such systems.
2. Recognising that GPR targets offer optimum read channel performance in patterned media systems.
3. Identifying that the optimum read channel performance is observed for a patterned medium with no SUL.
4. Identifying that the use of hexagonally packed media offers improved read channel performance, particularly in the presence of jitter noise and TMR.
5. Demonstrating that the use of LDPC codes offers vastly improved BER performance, particularly in the presence of lithography jitter, and in addition a potential increase in storage density.

Publications & Presentations

1. EPSRC final report [pdf].
2. Improved Data Recovery from Patterned Media with Inherent Jitter Noise using LDPC Codes, I. T. Ntokas et al., accepted for publication IEEE Trans. Mag., 2007.
3. High Resolution MFM Study of E-Beam Lithography Patterned CoPt Nanodots, B D Belle et al., J. Appl. Phys., vol 101, 2007 [pdf].
4. The Effect of Island Distribution on Error Rate Performance in Patterned Media, P W Nutter et al., IEEE Trans. Magn., vol. 41(10), pp. 3214-3216, 2005 [pdf].
5. An Investigation of the Effects of Media Characteristics on Read Channel Performance for Patterned Media Storage, P W Nutter et al. , IEEE Trans. Magn., vol. 41(10), pp. 4327-4334, 2005 [pdf].
6. Evaluation of read channel performance for perpendicular patterned media, I T Ntokas et al., J. Magn. Mag. Mat., vol. 287, pp. 437-441, 2005 [pdf].
7. Effect of Island Geometry on the Replay Signal in Patterned Media Storage,P W Nutter et al., IEEE Trans. Magn., vol. 40, No. 6, pp. 3551-3558, 2004 [pdf].

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Created by Paul Nutter