Modeling the washboard effect at the head/disk interface

A model is presented that accounts for the observation of periodic lubricant ripples formed when a slider is flying on-track over a lubricated disk surface. It is shown that lubricant flow modulation from the air shear stress due to the low flying slider acting as a spring is responsible for the observed corrugation, as repeated flying over the same track enhances the effect. This is somewhat moderated by the relaxation of the lubricant perturbation, by surface diffusion. Depending on the relative magnitude of the shear and diffusion processes, the system can find itself into regions of stability where small perturbations decay away, or regions of instability where they increase exponentially. Instability is enhanced for lower fly height and higher disk rotational frequency, making it a challenge for future growth in disk drive performance and areal density.