Evaluation of Head Wear Durability Due to Asperity Contact Based on Replenishment Velocity Analysis of Sub-Monolayer Lubricant in Hard Disk Drives

In magnetic hard disk drives, it is important to evaluate head wear durability in near contact regime because the head-disk spacing has to be reduced to ～1nm to achieve a high density recording above 1 Tb/in2. This paper presents an evaluation method of the replenishment speed of a mobile lubricant scar caused by asperity contacts. The replenishment speed of sub-monolayer lubricant into a removed scar was analyzed by using the two-dimensional long wave equation on the basis of continuum mechanics. Then, a generic evaluation chart to estimate the removed lube scar width with 50% replenishment after one disk rotation was proposed in relation to the thickness and viscosity of the lubricant. Next, the effective lubricant viscosity of an actual thin lubricant layer was identified by comparing the measured lubricant replenishment process and its numerical simulation. From the analysis of contact pressure and width for roughness and defect asperities of disk surface in addition to the above results, the minimum possible head-disk spacing with 50% lube replenishment for reliable read-write operation and critical asperity contact conditions resulting in head wear and medium scratch are discussed.