Air bearing slider dynamics and stability in hard disk drives

The disk drive industry is continuously trying to achieve higher data storage densities, faster data transfer rates, and higher reliability at lower cost. The new storage density goal of 3 Tbit/in2 dictates smaller magnetic spacing and a reduction in the slider's vibrations. With tighter limits on slider vibrations and elevated excitation due to intermolecular forces, electrostatic forces, windage and shock, small variations of slider pose a potential threat of head-disk interface (HDI) failures. Thus, this dissertation aims to study the slider dynamics and stability in hard disk drives and to propose strategies not only for reducing the slider vibrations, but also for enhancing the stability of the HDI.; The research presented here addresses three objectives. Firstly, there is a need to reliably predict the system behavior at high disk rotation speeds and at low mechanical spacing. Researchers in the past have used a simple model consisting of a slider and an air bearing model, while completely ignoring the dynamics of the head-stack assembly (HSA) and the disk. It has been shown that the system dynamics predicted by these models is significantly different from the actual system response (measured experimentally) during slider-disk contact/impact, aerodynamic forcing, shocks, track seek, load-unload etc. In this dissertation a new simulation program is proposed which seeks to predict the system dynamics by including the HSA and the disk model for the first time.; The second objective is to investigate the slider dynamics and stability caused by intermolecular and electrostatic forces acting on the slider and the aerodynamic forces acting on the HSA and the disk. The effect of intermolecular and electrostatic forces on the slider's 6 degrees-of-freedom (DOF) and the interaction of the length scale of the slider-disk topographies with the slider vibrations and stability are investigated for the first time in this dissertation. The first ever numerical investigation of slider vibrations due to aerodynamic forcing of the HSA and the disk considering the effect of the HDI forces is also reported here. Further, the effects of several flow mitigation devices, smaller suspensions and reverse spinning disks on flow-induced slider vibrations are investigated.; But even if all targets for reduced mechanical spacing and tighter limits on slider vibrations are met, the superparamagnetic limit restricts the maximum achievable recording density on the conventional media to about 0.5-1 Tbit/in 2. Patterned media has been proposed as an alternative to overcome this limit and achieve recording densities greater than 3Tbit/in2. But one of the main obstacles to patterned media is achieving stable mechanical slider-disk spacing. Thus the third objective of this dissertation is to study the slider's flying characteristics on a patterned media. The dynamics of the slider along all 6 DOF and its stability is investigated for the first time in this dissertation. Optimal patterned disk topography is also proposed for maximum stability of the slider over patterned disk surface.