Fig. 1: Schematic diagram of a thermal protrusion slider ‘surfing’ on the lubricant above a spinning hard disk. This method of recording, in which the slider physically contacts the disk, could allow higher density data storage.
© 2009 Wei Hua
Numerous studies on improving the storage capacity of computers have been conducted recently, with a strong emphasis on making data bits as small as possible.
Yet the same could also be achieved through relatively simple changes to the hardware of disk drives. Wei Hua, Bo Liu and co-workers at the Data Storage Institute of A*STAR, Singapore1, have now provided theoretical support for a new hard disk interface design proposed previously by Bo Liu’s team2.
In a hard disk drive, the electromagnetic reading and writing of data is performed by a ‘slider’ that flies just above the fast rotating disk. Calculations by Hua and co-workers support the notion of a new type of slider-disk interface, where the slider would actually touch the disk without damaging it, thus allowing higher density recording.
A slider typically flies less than ten nanometers above a disk. Unfortunately, if the slider goes any lower than this, it risks hitting occasional imperfections on the disk surface. This means the slider will have only intermittent contact with the disk, like a car bouncing over speed bumps on the road.
The crucial parameter to control is the ‘flying height’ of the slider, which is the clearance between the mean roughness planes of the slider and the disk surfaces. “The closer the head is to the recording media, the higher the recording density,” notes Hua. However, it was thought for many years that regular contact between the disk and slider would adversely affect reading and writing performance. Contact recording could now be possible thanks to a device called the thermal protrusion slider, which provides a clever way of controlling the flying height (Fig. 1).
“A thermal protrusion slider has a heater close to the disk read/write heads,” explains Hua. “When a current is applied, the heat produced will make the slider expand, and hence reduce the flying height.”
In light of these promising technical developments, Hua and co-workers investigated the forces involved when a slider comes into contact with a disk, surrounded by a lubricant. Despite some tricky computational challenges in modeling the fluid dynamics of the lubricant, their models reproduced some contact force measurements for thermal protrusion sliders operating at different voltages.
The researchers also predicted the tolerance budget for ‘lube surfing recording’, which could be the ideal type of contact recording. Hua now hopes to assess issues of flying stability, and the accumulation of lubricant on the slider.
The A*STAR-affiliated authors in this highlight are from the Data Storage Institute.
