A parametric study of head-disk interface instability due to intermolecular forces

This paper presents a nonlinear dynamic analysis of the head-disk interface by including intermolecular adhesion forces for sub-5-nm flying air-bearing sliders. Experimental evidence shows that one of the major roadblocks in achieving ultralow flying heights is the stability of the head-disk interface. It is found that the inclusion of intermolecular forces between the slider and disk in modeling the head-disk interface leads to dynamic instability of the slider. A parametric study is conducted showing the dependence of stability/instability on the variables. By understanding the effect each parameter has on stability, we can achieve air-bearing surface and disk morphology system design guidelines. From this study, it is found that the head-disk interface can become unstable due to intermolecular forces below a flying height of about 6 nm. However, from the results of the parametric study, it is shown that a head-disk interface can be designed such that it maximizes stability, although the instability cannot be attenuated completely. By minimizing the intermolecular adhesion forces and the flying-height modulation, and by maximizing the air-bearing stiffness and damping, we achieve maximum stability. Also, it is found that the stiffening effect of the air-bearing film increases the stability. The implications of this study are that the head-disk interface stability is dramatically compromised in the sub-6-nm flying-height regime and that the glide height of "super-smooth" disks will not only be a function of the disk\´s morphology, but also the intermolecular adhesion force induced instability of the slider.