Head-disk interface dynamics of ultra-low flying air bearing sliders for hard-disk drive applications

The dynamics associated with the head-disk interface (HDI) in hard-disk drives are studied for ultra-high magnetic recording areal densities. Slider dynamics and flying-height modulation (FHM) are studied both experimentally and by simulation. The experimental results are explained by modeling and simulation to understand and control FHM through design guidelines.; For a steady-proximity flying interface (occasional contacts between the slider and disk) the FHM is composed primarily of repeatable motions induced by the disk morphology. This FHM consists of three frequency regimes, which can be characterized as (1) geometric, (2) dynamic, and (3) zero response FHM. The geometric FHM is the major contributor for certain combinations of sliders and disks, and it is studied in detail in order to understand its cause and to minimize the effects of this component.; A comparative study of the dynamic performance of sliders as a function of form-factor (size) revealed counter intuitive results. It was previously believed that as the form-factor decreased, the FHM and dynamic performance would improve. However, in this work we found that this conventional understanding is not always the case. As the form-factor decreases, the air bearing stiffness usually decreases and the geometric FHM is not necessarily minimized.; As the slider transitions from steady-proximity to unsteady-proximity, a certain nonlinear characteristic of the air bearing slider system becomes more pronounced. This nonlinearity is studied using joint-time frequency analysis in which a highly non-stationary response causes unusual complexities in understanding the system's behavior in the frequency domain. Also, the cause of an observed “snapping” effect from steady-proximity to unsteady-proximity is explained by incorporating near-contact triggered adhesion forces between the slider and disk through modeling. The experimental results showing this “snapping” effect as well as the presence of an observed flying-height hysteresis can be explained by inclusion of these adhesion forces. These results suggest that there is a lower limit of the flying-height below which a slider cannot fly stable. This lower FH limit may preclude the use of traditional air bearing sliders for areal densities greater than 1 Tbit/in2 , and it is likely to require special designs of the slider's air bearing surface to reach 1 Tbit/in2.