Influence of Ultra-Thin Film Tribology on Hard Disk Areal Storage Capacity

In most industrial applications, a thin film of lubricant improves the tribological behaviour of the load carrying conjunctions. Modern hard disk drives are no exception, where one of the challenges is the progressive demand for higher data storage capacity, while decreasing the physical size of the device. This paper investigates the load carrying capacity of an ultra thin lubricant film formed between the hard disk drive platter and its flying read-write head slider. Hydrodynamic wedge action is responsible for the entrainment of a film of perfluoropolyether into the conjunction, but does not account for the main share of the load carrying capacity of the very thin discretized film, several molecular diameters of the fluid in thickness. It is shown that the main mechanism of pressure generation is in fact the solvation effect. Additionally, starvation of contact may well occur, further exacerbating the thinness of a lubricant film. There is often a cavitation region at the contact exit, which is followed by film reformation, changing the density distribution of lubricant on the surface and consequently the attainable data storage density. This is caused by the observed clumps of lubricant in the reformation zones (a phenomenon referred to as lubricant mogul) which can also cause transient motions of the read-write head.