Adhesion Forces for Sub-10 nm Flying-Height Magnetic Storage Head Disk Interfaces

Abstract

A quasi-dynamic adhesion model is used to calculate the intermolecular adhesion forces present in ultra low flying Head Disk Interfaces (HDI’s). The model is a continuum-based micromechanics model that accounts for realistic surfaces with roughness, molecularly thin lubricants, and is valid under both static and dynamic sliding conditions. Several different levels of surface roughness are investigated ranging from extremely smooth surfaces having a standard deviation of surface heights σ=2 Å to rougher interfaces with several nanometer roughness. It is found that when the flying-height is greater than 5 nm, there are no significant adhesive forces, whereas for flying-heights less than 5 nm, adhesion forces increase sharply, which can be catastrophic to the reliability of low flying HDI’s. In addition to roughness, the apparent area of contact between the flying recording slider and the magnetic disk is also found to significantly affect the magnitude of the adhesion forces. The adhesion model is validated by direct comparisons with adhesion “pull-off” force measurements performed using an Atomic Force Microscope with controlled probe tip areas and magnetic disks having different lubricant thickness.