Nanomechanical data storage

Researchers from IBM’s Zurich  research facility have shown the prototype of a MEMS-based nanomechanical storage device for the first time at the CeBit show in Germany.

Known internally as the ‘Millipede’, the new device is capable of achieving data storage densities of more than 1TBit (1000GBit) per square inch – the equivalent to storing the content of 25 DVDs on an area the size of a postage stamp.

At its heart is a two-dimensional array of V-shaped silicon cantilevers, each 70 micrometers long that are arranged in the form of an array on a 10 mm x 10 mm chip.

For the device to perform its reading, writing, erasing or overwriting functions, the small cone shaped tips of the cantilevers are brought into contact with a thin film of a cross-linked polymer coated on a silicon substrate, which is moved in the x- and y-directions.

Individual bits are written by heating the tip to a temperature above the glass transition temperature of the polymer by means of a heating resistor integrated in the cantilever. The polymer then becomes softer, allowing the tip to indent a the film by a few nanometres.

To read out data from the device, the cantilever's reading sensor, which is separate from the tip, is heated slightly. As the polymer film is scanned under the tip, the tip moves into the indent and cools down. The cooling results in a measurable change in the electrical conductivity of the sensor, allowing data to be read from the device.

To overwrite data, thermo-mechanical effects cause the stressed polymer material around a newly created bit to relax. Thus, existing pits can be ‘erased’ by creating new pits very close to the old ones.

The IBM researchers say that they have demonstrated that the new form of memory device can handle more than 10,000 read write cycles.

The MEMS assembly (16.5 mm × 17.5 mm × 1.2 mm) incorporates the read/write 2D cantilever array, the micro-scanner, and the polymer medium.

The cantilever tips are brought into contact with the storage medium which is moved in the x- and y-directions for reading, writing, and erasing. The storage medium is positioned with nanometre-scale accuracy relative to the cantilever array.