Head-disk Interface Failure Research Articles

Study on the Thermal Decomposition of D-4OH PFPE Lubricant by Reactive Molecular Dynamic Simulation for HAMR

Heat-assisted magnetic recording (HAMR) is one of the ways of ultrahigh density storage technology. The pulsed laser in the HAMR head heats the nano-region of the disk to Curie temperature. The laser heating causes the decomposition of the PFPE lubricant, which indirectly leads to the failure of head-disk interface (HDI). The reactive molecular dynamics (MDs) simulations are performed to research the thermal decomposition of single and multiple D-4OH lubricants. The effect of three different heating rates on the thermal decomposition process of a single D-4OH lubricant is investigated. The decomposition processes of single and multi-D-4OH molecular chains are the same: the functional end groups degrade first and then the main chain. These results are useful for the optimization of PFPE lubricants for HAMR disks.

Lubricant reflow after laser heating in heat assisted magnetic recording

In heat assisted magnetic recording (HAMR) technology for hard disk drives, the media will be heated to about 500 °C during the writing process in order to reduce its magnetic coercivity and thus allow data writing with the magnetic head transducers. The traditional lubricants such as Z-dol and Z-tetraol may not be able to perform in such harsh heating conditions due to evaporation, decomposition and thermal depletion. However, some of the lubricant depletion can be recovered due to reflow after a period of time, which can help to reduce the chance of head disk interface failure. In this study, experiments of lubricant thermal depletion and reflow were performed using a HAMR test stage for a Z-tetraol type lubricant. Various lubricant depletion profiles were generated using different laser heating conditions. The lubricant reflow process after thermal depletion was monitored by use of an optical surface analyzer. In addition, a continuum based lubrication model was developed to simulate the lubricant reflow process. Reasonably good agreement between simulations and experiments was achieved.

Effect of volatile organic contamination on head-disk interface tribology and a method for its reduction

Volatile organic contamination is known to be one of the factors to cause the failure of head-disk interface (HDI). Therefore, reduction of its harmful effects and improvement of the stability and reliability of HDI is becoming an important issue. In this study, the effects of some model compounds of volatile organic contamination on the tribological characteristics of HDI were systematically investigated using a contact start/stop (CSS) tester. The slider surface after the CSS tests was analyzed using Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). Transfer of lubricating oil onto the slider surface was detected after the CSS tests. The organic contaminants promoted the transfer and resulted in high and unstable friction force. Fluorinated self-assembled monolayers (SAMs) were applied on the slider surface for reducing the transferred amount of the lubricating oil. Tribological performance of the slider coated with the SAMs and the transfer amount of lubricating oil onto the slider surface in the presence of contaminant was investigated. The friction force was low and stable in the case of the SAMs coated slider even under environmental contaminant. This result could be explained by the reduction of the transferred lubricating oil because the SAMs that coated on the slider surface were low surface energy.

Effect of hard-disk drive spindle motor vibration on dynamic microwaviness and flying-height modulation

In order to achieve higher recording densities up to 1 Terabit per square inch using conventional magnetic recording technologies, the recording slider will need to be physically spaced very close to the rotating disk, possibly via the use of an air-bearing surface. However, as the recording slider is flying at such ultra-low spacing of few nanometers over a high-speed rotating disk, it is experiencing disturbances from various different sources and of a wide frequency range. These disturbances may cause the recording slider to vibrate significantly, a condition known as flying-height modulation (FHM), which may result in data loss and possibly head–disk interface failure. A significant source of slider excitation is due to low frequency surface topographical features of the rotating disk, termed dynamic microwaviness. Dynamic microwaviness is a dynamic property of the disk and differs from regular topographical microwaviness, which is a static property. Most research works on dynamic microwaviness and FHM have been focused at the component level, using somewhat idealized conditions, such as high performance air-spindle motors that exhibit very low vibration amplitudes. In this paper, actual hard-disk drive spindle motors are used to investigate the effect of spindle motor vibration on dynamic microwaviness and FHM. It is found that there is a clear connection between spindle motor vibration and dynamic microwaviness that affects FHM.

Pole-Tip Protrusion Effect on High Data Rate Recording Performance

Write pole-tip protrusion (PTP) effect on the overwrite performance at high recording data rate is discussed. It is shown that the head thermal expansion during the write process may lead to the degradation of overwrite value at high recording data rate. Overwrite degradation is caused by head-disk interactions when a high-frequency pattern is written. Appropriate selection of the disk lubricant can reduce the effect of the write PTP and increase the write current setting margin. At elevated drive temperatures, excessive PTP can cause head-disk interface failure. A write timing method allowing for the recording head to cool between the write cycles is proposed. A method of head-disk interface testing and a method of mapping the head-disk interactions are further described.

Effect of particulate concentration, materials and size on the friction and wear of a negative-pressure picoslider flying on a laser-textured disk

The effect of particulate contamination on friction and wear between a negative-pressure picoslider and a laser-textured disk has been studied. Particles of different concentration, materials and size were injected at the head-disk interface consisting of disks with various textures and slider types at different speeds. Durability increases and coefficient of friction decreases as the disk speed is increased in a contaminated environment. Frictional characteristics and durability in the data zone were better than those in the laser-textured zone. It was also found that durability of head-disk interface (HDI) decreased as the particle concentration increased. Hard particles and large particles made the HDI failure early and resulted in an extensive damage to the slider and disk surfaces. The interface durability with the picoslider was better than that with the nanoslider at any condition in a contaminated environment. Based on the test results, the mechanisms are proposed to explain the reasons why durability with the picoslider is superior to that with the nanoslider and the mechanism of the HDI failure with the picoslider is also presented.

Track seeking, head-disk spacing variation and head-disk interface failure

Track seeking and the slider-disk space variation during track seeking are becoming more and more serious concerns when technology moves to 0.8-1.5 /spl mu/m gap flying-height. This paper reports results of in-situ experimental investigations of the slider's dynamic flying performance during track seeking. A partial erase method and a slider-disk resistance method were used in the investigation. Results indicate that the suspension's vibration during track seeking plays an important role in the flying height vibration of slider. Furthermore, results indicate that the likely zone of slider-disk impact can be revealed by monitoring the resistance and the VCM current waveform simultaneously. A model is proposed also to explain the relationship of flying particles inside disk chamber, the slider's dynamic performance during track seeking and the flying particles induced HDI failure.

Particle build-up on flying sliders and mechanism study of disk wear and head-disk interface failure in magnetic disk drives

A novel experiment was designed to promote the understanding of the mechanism of disk wear caused by particulate contamination. Obtained results suggest that the slider picks up particles and accumulates them on its surfaces as it flies above the disk. The instability of the flying slider, especially that induced by track seeking, leads to slider-disk impact which releases the accumulated particles. This results in abrasion amongst the slider, the contaminants, and the disk. The investigation also indicates that the outer two surfaces in a disk-stack and the corresponding sliders have higher likelihood of capturing flying particles. A model has been proposed to explain the observed phenomena.

Organic buildup on slider leading edge tapers and its effect on wet stiction

The phenomenon of organic mixture buildup on slider leading edge tapers (LETs) was studied experimentally by conducting contact start/stop (CSS) tests in a humidity chamber. The effect of organic buildup on wet stiction performance of head/disk interface (HDI) was investigated. It is found that high humidity leads to higher rate of PFPE lubricant loss at disk landing zone and significant material buildup at the end of head slider LET surfaces. Such changes at the HDI cause irreversible high stiction, large stiction modulation, and, therefore, shorter CSS life. Organic silicone vapor film from silicone outgassing speeds up to the buildup process and leads to early HDI failure. Reducing LET organic buildup can extend wet CSS life.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>