Laser-lubricant interaction has been a critical reliability issue in heat-assisted magnetic recording (HAMR) system, one of the next generation hard disk drive solutions to increasing data storage. The lubricant improves the system performance by passivating the surface against contamination, minimizing friction, and preventing corrosion. However, the lubricant in HAMR undergoes evaporation, decomposition and diffusion under thermal exposure, and reflow afterwards. In-situ diagnosis for the lubricant is valuable to the tribological longevity of HAMR hard disk drives.  

Figure 1. Head-disk interface in HAMR.

This research presents an innovative approach to in-situ characterization of laser-lubricant interaction in HAMR hard disk drives. A thermal scheme has been proposed that significantly improves the ability to measure lubricant dynamics with sub-angstrom resolution (~0.2 Å) and fast response time within seconds, compared to conventional ex-situ methods like optical surface analyzer (OSA).

The research draws inspiration from the thermal barrier effect of nanometer-thick lubricants on near-field thermal transport. This effect allows for precise measurement of lubricant thickness and dynamics. The team at the University of California at Berkeley and Western Digital Corporation has engineered a component-level HAMR test stage that mimics a real HAMR hard disk drive, enabling the study of laser-lubricant interactions under realistic operating conditions.

Figure 2. Thermal barrier effects of lubricant.

This innovative approach leads to several breakthrough measurements. For the first time, the study provides quantitative in-situ measurements of laser-induced lubricant depletion and subsequent reflow dynamics. These measurements reveal that the lubricant shows thermal stability up to 220 °C, above which depletion is proportional to disk peak temperature rise. The research also uncovers that the initial lubricant loss occurs at a much faster rate compared to subsequent loss.

Lubricant depletion under laser irradiation

Figure 3. Lubricant depletion under laser irradiation.

Lubricant reflow dynamics

Figure 4. Lubricant reflow dynamics.

One essential tool for these measurements is the thermal fly-height control mechanism, which allows precise adjustment of the air gap between the head and disk. Using an integrated microscale heater and thermometer in the HAMR recording head, the researchers could control and measure thermal transport across sub-nanometer air gaps. This setup, combined with a rotating disk featuring a magnetic layer, carbon overcoat, and lubricant layer, enables the study of thermal transport and lubricant dynamics at sliding speeds of 5-40 m s^-1, six orders of magnitude higher than previous near-field thermal transport studies based on atomic force microscopy.

This work not only advances our understanding of HAMR technology but also provides a powerful tool for real-time, in-situ analysis of nanoscale thermal and tribological phenomena. The methods and findings presented in this paper are likely to inspire further research and development in the fields of data storage, nanotechnology, and thermal management.

The research was supported by Computer Mechanics Laboratory, University of California at Berkeley and Western Digital Corporation. The paper, titled "In-situ sub-angstrom characterization of laser-lubricant interaction in a thermo-tribological system," was published on October 5th, 2024.