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Nanopositioning for probe-based data storage [Applications of Control]

Probe-based data-storage devices are being considered as an ultra-high-density, small- form-factor alternative to conventional data storage. The probe-based data-storage concept is derived from scanning-probe microscopy, where nanometer-sharp tips are used to interrogate and manipulate matter down to the atomic scale. One implementation of this concept is based on a thermomechanical principle for storing and retrieving data encoded as nanometer-scale indentations in thin polymer films. Ultra-high densities of more than 1 Tb/in2 have been achieved with this scheme. A small-scaleprototype system comprising all of the elements of a probe- based data storage device has been developed. One of the key challenges is the positioning of the storage medium relative to the read/write probes with nanometer-scale accuracy. A microscanner with X/Y motion capability is used to position the storage medium. Position information along both scan directions is provided by a pair of thermal position sensors. In addition, medium-derived position information provides a measure of the cross-track deviations in the Y-scan direction. Control architectures for both scan directions are presented. The X control architecture relies on thermal position sensors alone, whereas the Y control architecture relies on both the thermal position sensors and the medium-derived PES. Nanometer-scale positioning accuracies are achieved over a bandwidth of a few hundred hertz. Read/write demonstrations with sufficiently low error rates demonstrate the efficacy of the nanopositioning schemes employed.