Tribological and Dynamic Study of Head Disk Interface at Sub-1-nm Clearance

As the areal recording density approaches to 1 Tb/in², the spacing between magnetic heads and medium is decreased to sub-1-nm regime with the application of dynamic flying height (DFH) technology. Challenges in tribological flyability and reliability in the head-disk interface (HDI) become formidable at such ultra-low spacing, and it is necessary to achieve from both media and head design. It is also essential to have a better touch-down (TD) detection method and more accurate back-off spacing control for sustainable tribological performances. In this paper, the dynamics and wear during TD process were studied first. The characteristic TD modes were identified by laser Doppler vibrometry (LDV) and the TD induced wear was quantified using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that different TD stages correspond to different TD modes and amount of TD wear. It is found that the identification and capture of the characteristic TD modes, especially the first TD mode, are the key factors to timely detect TD and minimize the TD wear. The tribological performances at sub-1-nm clearance were then investigated with respect to both head and media design. The slider dynamics over a bump was studied to simulate the head reliability when the head intermittently contacts the media. It is found that air bearing surface (ABS) design of the head has a significant influence on the settling time when head passes through the bump. In addition, the flyability over a wavy surface (i.e., media run-out) was also studied to understand the TD repeatability. The results show that media run-out strongly affects TD repeatability and back-off spacing accuracy. Consequently, spacing control to sustain the reliability at sub-l-nm clearance is necessary. With in-depth understanding of dynamics and tribological performances (i.e., flyability and reliability), media and head ABS design are the key factors to achieve a sustainable HDI at sub-1- - -nm clearance.