Teflon-Like FCOC Coating on Glide Heads for Stick-Slip Alleviation
Original Publication Date: 2002-Aug-17
Included in the Prior Art Database: 2003-Jun-20
With the current technology, as the hard disk areal density increases, the head-disk gap must decrease. As the distance between the head and the disk surface (hereinafter as “fly height”) decreases, molecular interactions between the head and the lubricated disk surface become increasingly dominant. The lubricant, head, and disk material all factor into determining the threshold fly height where the disk and head detrimentally interact with one another (hereinafter as “stick-slip height”). This interaction saturates the glide head piezoelectric transducer, resulting in false indications of disk topography anomalies and thus decreasing the glide head effectiveness. To counteract this phenomenon, a fluorinated carbon overcoat (FCOC) is applied to the head, resulting in a reduced stick-slip height, by as much as 33 percent. Reduction of the stick slip height allows lower fly heights and more accurate glide testing. “Stick-slip” occurs when the head and the disk lubricant interact via Van der Waals forces. On a molecular level, when two materials are brought near one another, there is an attractive force, the strength of which is partially determined by the surface energy of each material. By manipulating the surface energies of the two materials, the amplitude of the forces in action may be altered. The typical surface energy of the carbon overcoat of a head is approximately 50 erg/cm2. When the Teflon-like FCOC is applied to the head, the surface energy is reduced to approximately 12 erg/cm2. The surface energy of a typical hard disk is approximately 20 erg/cm2. At very low fly heights, the differences in the surface energies between a disk and an uncoated head will cause the lubricant to “jump” from the disk to the head. A dynamic “lubricant bridge” is formed and the piezoelectric transducer is excited. Application of the Teflon-like FCOC lowers the surface energy of the head below that of the disk itself and thus reduces the propensity of the lubricant bridge formation. Teflon-like FCOC’s can be applied in a controlled, economical process necessitating minimal change to the head gimble assembly (HGA) process. Evaluation of both glide heads for disk topography testing and file data heads have shown that the additional layer affects the performance of the air bearing surface (ABS) or the sensitivity of the glide head. Hard disk drive reliability testing shows no change by the introduction of the Teflon-like FCOC’s.