The Role of Relative Humidity, Surface Roughness and Liquid Build-Up on Static Friction Behavior of the Head/Disk Interface

Stiction at the head/disk interface has become one of the major concerns as smoother surfaces are required to achieve lower flying heights of magnetic heads over magnetic disks. In this paper, static friction forces on three types of disk samples with different surface roughness values were measured at various relative humidities. It was found that static friction coefficients were well correlated with total thickness of liquid (lubricant and adsorbed water) at the head/disk interface. The experimental data also agreed fairly well with the calculated values based on a proposed stiction model. It is implied in the stiction model that the bearing ratio or the shape of asperity height distribution, especially the part of high asperities, determines the stiction force. Moreover, long-term stiction was investigated on the unlubricated disk surfaces at 80 percent relative humidity and on the lubricated disks at 5 percent relative humidity to separate the effects of water build-up and lubricant build-up at the head/disk interface. It appears that long-term stiction occurs only when enough mobile lubricant is present and the thickness of liquid at the head/disk interface is close to a critical thickness value which is related to surface roughness values.