Laser-Induced Thermo-Desorption of Perfluoropolyether Lubricant from the Surface of a Heat-Assisted Magnetic Recording Disk: Lubricant Evaporation and Diffusion

Abstract

Heat-assisted magnetic recording (HAMR) storage technology will thermally stress the lubricant film typically applied to the storage disk surface. Different lubricant loss and morphology change mechanisms have been hypothesized to occur during information writing. A loss to of the lubricant film will dramatically affect its overall mechanical and chemical performance of the headdisk interface, decreasing its reliability and its durability. Thus an all optical pump-probe method was used to study the effect of fast thermal transients (10 6 K/s) on a lubricant film on HAMR media. Thermal transients (Bhushan and Cheng in J Appl Phys 81:5390, 1997) with peak temperatures above the HAMR media Curie temperature (T c ) were found to remove by evaporation the lubricant within the heated region creating a lubricant depression in the otherwise continuous film. No accumulation of lubricant volume was observed to take place in the cooler regions of the thermal spot, indicating that thermocapillary shear stress is not an important mechanism of lubricant thickness change with the optical spot size used (65 lm). The onset of lubricant loss was observed to begin at approximately 610 K and was totally removed at 823 K. The change in depth of the lubricant depression with time showed that no structural terms contributed to the disjoining pressure for the lubricant thickness range studied. From this change, the diffusion coefficient of the lubricant on the carbon overcoat surface was determined to be 1 9 10 -13 m 2 /s by fitting Fick's second law to the normalized lubricant thickness. The importance of these observations on the operating HAMR head-disk interface is discussed.

Z-Tetraol Reflow in Heat-Assisted Magnetic Recording

“…From a slider-disk interface perspective, the thermal stress is expected to challenge the robustness of today's protective carbon and boundary lubricant films. Numerous studies have been spawned to answer the question of whether or not the current carbon and lubricant "tribological layers" can survive HAMR technology [2][3][4][5][6][7][8][9][10][11].…”

“…From strictly a boundary lubricant perspective, experimental studies have shown that laser heating removes lubricant film from the disk surface [2,8,9]. Depending upon the read-write duty cycle, the mobility of the boundary lubricant film, and the local supply of the lubricant film, reflow from the surrounding area into the thickness-depleted area may, or may not, occur at a fast enough rate to maintain tribological robustness under HAMR conditions.…”

“…Lubricant reflow has not been required of PMR media thus far. Several papers report on the experimental reflow kinetics following laser irradiation [2,16]. For example, approximately 24 hr was needed to recover a 12 Å Z-Tetraol trough having a 65 µm diameter [2].…”

“…Several papers report on the experimental reflow kinetics following laser irradiation [2,16]. For example, approximately 24 hr was needed to recover a 12 Å Z-Tetraol trough having a 65 µm diameter [2]. In other reflow experiments, reflow kinetics into a 20 Å Zdol trough having a 1 µm diameter required ~35 millisec for 50% recovery [17].…”

Perfluoropolyether Boundary Lubricants Based on the Star Architecture

“…Most experimental laser irradiation studies on PFPEs have been conducted on much larger ~ 10 µm (10,000 nm) spot size so HAMR-realistic length scales have not yet been approached. Under these conditions, as much as several Å of lubricant film thickness could be removed depending upon laser power and exposure time [8][9][10][11]. Based upon these data, there is little doubt that HAMR disk lubricants with improved thermal stability will become an important lubricant design feature.…”