Tri-state dynamic model and adhesive effects on flying-height modulation for ultra-low flying head disk interfaces

Abstract

Physical spacing between a flying slider and a rotating disk is projected to be 3 nm in order to achieve extremely high areal recording densities of 1 Tb/in2. In such ultra-low flying-height regimes, two imminent obstacles that need to be overcome are intermittent head/disk contacts and strong intermolecular adhesive forces at the head/disk interface (HDI). Head/disk contact can cause large vibrations of the recording slider and possibly damage the disk and slider due to large contact forces. Strong adhesive forces disturb the balance of forces in a flying slider by pulling it down onto the disk and increasing the possibility of catastrophic HDI failures by doing so. This paper describes a dynamic model that includes contact and adhesive forces. Specifically, a lumped parameter single degree-of-freedom, three state nonlinear dynamic model representing the normal dynamics of the HDI and asperity-based contact and adhesive models were developed and coupled together to predict the performance of ultra-low flying sliders. The validity of the proposed dynamic model was confirmed in terms of flying-height modulation (FHM) by experimental measurements using ultra-low flying HDIs. It was found that the amplitude and frequency components of the dynamic microwaviness play an important role in slider dynamics. Furthermore, the effect of adhesive force on FHM was investigated and design guidelines for reduced FHM were suggested.