The physics behind lubricant transfer from disk to slider and lubricant accumulation on the slider in hard disk drives is explained. The effect of slider air bearing pressure on the lubricant transfer is discussed. It is found that the lubricant transfer is not affected by slider air bearing pressure. Lubricant molecular weight plays a dominant role in the lubricant transfer and lubricant accumulation. The amount of lubricant transfer and accumulation decreases dramatically with the increase in lubricant molecular weight. A thinner lubricant and higher bonding ratio of lubricant on disk surface reduce the lubricant transfer and accumulation obviously.
Pushing recording density towards tera-bit per square inch and beyond requires reducing flying height to 2.5-3 nm or below. One critical challenge at such ultralow flying height is the possible head-disk crash or instable head-disk spacing due to short-range interaction forces, such as electrostatic force, intermolecular forces, lubricant interaction force, and so on. Slider design and design strategy are investigated in this work aiming at significantly increased stability of the head-disk spacing at ultralow flying height. Nonzero surface roughness leads to a roughness-limited possible minimum flying height. A stable head-disk interface requires a full air-bearing domination even at a roughness-imposed minimum flying height. Here, the air-bearing domination means that both air-bearing force and air-bearing stiffness are larger than the combination of various short-range forces and the corresponding stiffness. Investigations presented in this paper indicate that high pressure and high-pressure concentration technology are effective approaches to extending the domination of air-bearing force towards such a roughness-limited possible minimum flying height. Slider designs, proposed by authors, exhibit satisfying flying height stability even at the roughness-limited minimum flying height.Index Terms-Head-disk interface, magnetic hard-disk drive, magnetic recording, short-range interaction forces, tribology.
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