Mechanics and Tribology Problems for the Next Generation of Hard Disk Drives

Since the introduction of the first hard disk drive 50 years ago the areal density of data on a hard disk has increased by a factor of 60million.  The rate of increase has been between 50 and 100% per year.  The current density in commercial products is approaching 200 Gbit/sq.in., and the industry is scheduled to demonstrate 1 Terabit/sq.in. in 2008.  To achieve this goal requires about 2.5 million bits per inch along the tracks and 400,000 tracks per inch.  The mechanical requirements for this are seemingly unattainable.  It requires air bearing slider clearances to the disk of less than 2 nm, and the tracks need to have a pitch of 50 nm.

Previously the advances in areal density were made by mostly evolutionary improvements with a major breakthrough from time to time.  It is clear that the 1 Terabit goal cannot be achieved by evolutionary changes alone.  An air bearing spacing of only 2 nm has new destabilizing forces, such as Van der Waal’s forces and electrostatic forces.  Since the very smooth disks will still have some roughness, on the order of half a nanometer RMS and 10 nm peak-to-peak, some contact will occur between the slider and disk.  Reliability of the head-disk interface becomes even more of a challenge.  Also air turbulence excitations of the actuator-suspension system cause off-track vibrations that will most likely require dual stage actuators and control systems.  The superparamagnetic limit on the closeness of thermally stable magnetic polarization reversals points toward the need for structural isolation of data bits, possibly requiring patterned media.  This also has implications for the mechanical stability of the head-disk interface.

This series of two talks will focus on recent research in the Computer Mechanics Laboratory in the ME Department at UC Berkeley aimed at addressing some of these challenges.