Effect of Interfacial Roughness on Slider-Disk Interactions at Near-Contact Regime

One of the major efforts in reducing fly height (FH) in order to achieve higher recording areal density for hard disk drive, is to reduce slider-disk interfacial roughness. However, as roughness improves to the atomically smooth level, various interaction forces such as van der Waals force, electrostatic force, and intermittent contact force affect slider fly stability. In this paper, an electrostatic force manipulation methodology was employed to investigate roughness effect on slider-disk interactions at near-contact regime. In such methodology, an AC excitation with pre-determined frequency was applied across the slider-disk interface. First harmonic vibration response of the excitation was monitored. Such vibration response is sensitive to various interaction forces, as FH is reduced to near-contact regime. The phenomena observed were verified with static and dynamic simulations, using self-developed ABsolution simulation software. It was found that disk with higher roughness has larger adhesive force gradient and hence larger first harmonic vibration at near-contact. First harmonic vibration dip was observed near touchdown point. Simulation result suggests that the phenomenon is due to time-averaging effect of slider intermittently “snap” to the disk surface. It was found that magnitude of the vibration dip is surface roughness dependent. At contact regime, nonlinear contact stiffness-based contact detection is highly sensitive for smooth surface. Abrupt transition of low to high vibration state of smooth surface during contact is attributed to larger adhesion hysteresis effect.