Published: Jan 2008
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A HARD DISK DRIVER (HDD) AS A HIGH SPEED DIGItal recording system has been a main part of the computer. It also has been widely used as a mobile data storing set in almost all electronic devices, including a video recorder, camera, etc. The recording density of a hard disk driver has been increasing at a high rate of 100 % per year in the past ten years. It is much faster than the rate of the Moore's law for silicon devices (̃50 %) . It is expected that the recording density will increase to 1,000 Gbit/ in.2, and the fly height will decrease to about 3 nm in the next several years [2,3]. There are three major challenges that tribologists are facing today. The first is how to make solid protective coatings, i.e., diamond-like carbon (DLC) layer, with a thickness of about 1 nm without any micro-pinholes; the second is how to make a lubricant film about 1 nmon the surface of a disk or head to minimize the wear, friction, and erosion; and the third is how to control the vibration of the magnetic head and its impacting on the surface of a disk. The biggest challenge to produce an ultra-thin (about 1 nm) overcoat is to make the coating free of pin-holes while maintaining the durability and tribological properties. In an HDD system, pin-holes can cause much more contaminants from all sources, such as outgas compounds from polymeric foam components, pressure sensitive adhesives, ionic residues from improperly cleaned components and ambient pollutants, which can be detrimental to the tribology and durability of the HDD. Therefore, efforts have been made mainly on the improvement of carbon film [4–7]. A stable lubrication is very important to the slider/disk interface as the demand of HDD life increases. The lubricant films need to have a strong adhesion and bonding with the carbon surface in order to be effective in reducing friction and wear of the hard disk interface . Organic films with one or a few monolayers have been used for lubrication of the HDD. Perfluoropolyethers (PFPEs) lubricant is one of the synthetic lubricants that are widely applied due to its excellent performances, such as chemical inertness, oxidation stability, lower vapor pressure, and good lubrication properties . Generally, lubricant is deposited on surfaces of a hard carbon overcoat of magnetic recording media. The lubricant and carbon films protect the underlying soft magnetic media from mechanical damage caused by intermittent contacts with the slider. During operation of an HDD, contacts between slider and lubricated film will result in the loss of lubricant in the contact region. Unless being continuously replenished, the film thickness of PFPE in the depleted contact zone will decrease with the increase of contacts, resulting in the loss of the interface life .
Tsinghua University, Beijing,
R&D Director, Kaifa Magnetics Ltd., Shenzhen,
Tsinghua University, Beijing,