Signal evaluation and data recovery in future ultra-high density hard disk drives
Keywords: magnetic storage, signal processing, nanotechnology, modelling, Matlab
The increasing demand for higher storage capacities in hard disc drives (HDD) will require a future storage density in excess of 1Tbit/in2, compared to today?s densities of ?360Gbit/in2. It is generally recognised that the use of bit patterned media (BPM) is one solution that will enable the increased storage capacities demanded in future applications. In BPM each bit is recorded to a nanostructured, isolated, single-domain magnetic island. However, there are a number of problems that prevent the commercial realisation of a HDD product incorporating BPM, most notably the variations in physical island properties, such as position and size, as well as magnetic properties. The effect of these variations is the introduction of errors when recording and reading data. On the whole such variations are unavoidable, although by careful design and fabrication they may be controlled. Understanding how these variations affect the ability to record and recover data is of prime importance to the development of any future HDD technology employing BPM.Project
We have developed a model of the data recovery process in a BPM storage system, written in the Matlab environment, which allows us to predict how variations in island geometry, in particular variations in island size and position, affect the recovery of data using a standard partial response maximum likelihood (PRML) read channel. The challenge of this project is to expand this work to enable the further investigation of the effect of imperfect media on the recovery of stored data. The project will involve the development of extensive simulations to extend the simulation capabilities of the existing software, including the realistic introduction of micromagnetic variations in island magnetisation, to produce a unique and powerful replay model that will enable accurate predictions of the ability to recover data in a BPM system. The modelling and signal processing skills developed as part of this project are pertinent to other fields, for example communications.
The NEST Group
The Nano Engineering & Storage Technology (NEST) group is housed in an integrated suite of staff offices, general-purpose laboratory space and class 100/1000 cleanrooms. The group is a founder member of the Manchester Centre for Mesoscience and Nanotechnology (CMN), which is based in the group?s laboratories and contains state of the art lithography tools for the fabrication and visualisation of nanoscale structures. The group also has facilities for characterising magnetic media including a purpose built alternating gradient field magnetometer and an ADE Technologies vector vibrating sample magnetometer.