Nanoscale stability and active control in hard disk drives

To achieve the areal density goal in hard disk drives of 1 Tbit/in² the minimum physical spacing between the slider and disk must be reduced to less than 5 nm. At such low spacing new nanoscale forces act between the slider and disk, such as intermolecular and electrostatic forces, which must be taken into consideration. These forces can create dynamic instabilities in the flying head slider, which are detrimental to its ability to reliably read and write data. This paper reviews the recent trends in data densities and size reductions in hard disk drives, showing that the transition to nanoscale phenomena is about to occur. Simple evolutionary developments appear to no longer work for increasing the areal data density. Some of the various alternatives for overcoming these new problems for sub-5 nm flying sliders are presented and discussed. We show the source and effects of the new short range forces and examine how various design parameters for air bearing sliders affect the instabilities. Then we present some alternatives to traditional flying head sliders, such as active control of PZT actuated flying sliders or contact interfaces for hard disk drives.