Effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives

This paper describes the effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three types of lubricants, which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability occurs as a result of slider–disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the lubricant film thickness should be designed to be approximately one monolayer thickness region in order to achieve contact recording for future head–disk interface.