Strategies to avoid head-disk instabilities due to adhesion in ultralow flying head-disk interfaces

Reducing the flying-height to sub-5 nm in hard disk drives is essential in achieving ultrahigh recording densities of the order of 1 Tbit/in². In order to minimize the risk of contact for such ultralow flying head-disk interfaces (HDIs), one needs to use extremely smooth disk and slider surfaces with RMS roughness values of the order of few ansgstroms. However, such super smooth interfaces are known to cause problems, such as strong attractive adhesive forces and, thus, catastrophic HDI crashes. In this paper, a systematic study specifically addressing strategies to minimize adhesion and, most importantly, to avoid head-disk instabilities or crashes due to adhesion is presented. The nonlinear adhesive forces are coupled with a nonlinear dynamic system model of the flying HDI, and a 3³ full-factorial design of experiments is performed to investigate the effects of roughness and geometrical parameters on adhesion, flyability, and stability of ultralow sub-5-nm flying HDIs. Based on analysis of variance and corresponding response analyses, strategies to avoid the detrimental effects of adhesion on flying HDIs are proposed.