An Experimental and Simulation Study of Touchdown Dynamics

Dynamic flying height technology has been widely employed for reducing the mechanical spacing between the magnetic heads and the disk. As the recording density of hard disk drives approach 1 Tbit/in², the spacing is decreased to sub 1 nm. At such low spacing, the touchdown (TD) dynamics becomes extremely critical. First, it affects the accuracy of the spacing setting, or TD detection. Second, it affects the hard disk drive reliability, such as writing modulation, wear, instability, etc. It decides how low the slider can fly stably and reliably. In this paper, we tried to have a better understanding of the TD dynamics with several designs of experiments first. We found that there were two stages in the whole TD process. In the first TD stage, a low frequency (30-150 kHz) vibration appeared. It was a suspension mode that was excited by the lubricant on the disk. In the second stage, a high frequency vibration (200-400 kHz) appeared. It was the second pitch mode of the slider air bearing excited by the contact between the slider and the disk. Based on these experimental observations, we propose modeling and simulation procedures with a combination of a full suspension model and a simplified air bearing model. Simulation can predict these two TD frequencies very well. Therefore, it could be applied to design head/disk interface to help achieve preferred TD behaviors.