The surface coverage effect on the frictional properties of patterned PFPE nanolubricant films in HDI

The surface coverage ratio of bonded and mobile phase of perfluoropolyether (PFPE) nanolubricant film on magnetic disk surface is an important factor in controlling the friction and durability in head/disk interface. In this paper, we report the optimum surface coverage ratio in a 1-nm-height ultrathin PFPE lubricant film for future hard-disk-drive technology. One-nanometer-height bonded and mobile PFPE nanolubricant films were deposited on magnetic disk surfaces and patterned by the photolithographic process. The surface coverage of lubricant film on the magnetic disk was varied in the range of 50% to 100%. Friction coefficients were measured by a ball-on-flat tribotester. The friction coefficients of patterned mobile lubricant films are lower than those of patterned bonded films. The friction coefficient of the disk coated with bonded lubricant film decreases linearly with increasing surface coverage. On the other hand, the friction coefficient of the disk coated with mobile lubricant film shows a minimum value at the surface coverage of 75%. This may be because the lubricant-free area prevents the ball slider and disk from stiction. We conclude that the optimum value of the surface coverage ratio in 1-nm-height ultrathin PFPE lubricant film in the aspect of low friction is 0.25, that is, two-dimensional pattern of 25% bonded and 75% mobile portion.