Papers

AVS1999 Session VM+MI+AS-TuA: Magnetic Recording: Head/Disk Interface and Overcoats

Tuesday, October 26, 1999 2:00 PM in Room 620

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		VM+MI+AS-TuA-1 Ultra Thin DLC Film as Magnetic Disks Overcoat X. Chu, B. Zhang, K.. Johnson (MMC Tech.) Sputtered DLC film of 100 to 200 A has been used for protective coating on thin film magnetic recording disk for years. DLC overcoat material of choice is hydrogen and/or nitrogen doped amorphous carbon deposited by magnetron sputtering. Increasing areal density in magnetic hard drives requires thinner overcoat to reduce signal loss between magnetic film and read head. Functional overcoat with thickness of 50A will be needed for next generation recording medium. Tribological performance of sputtered carbon films suffers at values below 100 A because of a degradation in physical properties. Alternative deposition techniques, such as ion-beam deposition process, create denser and harder films with the improved physical and tribological properties. In this paper we will present data on the deposition and characterization of 50 A to 30 A DLC films deposited both by sputter and IBD process. Process parameter effect on structure and mechanical properties of sputtered CNx, CHx film, and ion beam deposited CHx was studied. XPS and Raman were used to characterize film microstructure and showed the sputtered CNx film was mostly sp2 bonded. Tribology of the films were tested by Contact Start Stop (CSS) testers and the result of carbon wear can be correlated to AFM nano-wear test. 30A ion-beam deposited CHx film showed good CSS tribological performance comparable to 100 A sputtered films.
2:20 PM		VM+MI+AS-TuA-2 Tribological Properties of Protective Carbon Coatings Used in Magnetic Storage Devices Investigated on a Sub-Nanometer Scale A. Wienss (University of Saarbrücken, Germany); G. Persch-Schuy (IBM Germany Storage Systems Division); U. Hartmann (University of Saarbrücken, Germany) Ultrathin carbon coatings are used in the magnetic storage industry to protect sensitive sensor heads and magnetic media against mechanical damage. Such a damage can be modelled by artificially generated scratches using Scanning Force Microscope (SFM) techniques. Loading forces in the µN range are applied, resulting in scratches with residual depths of only a few Å. A special image subtraction technique is presented which allows careful analysis of tiny grooves even on rough surfaces. This technique compensates for drift effects during scanning. The scratching resistance of various a-C:H and CN_x films is determined. For a-C:H, an increasing amount of hydrogen results in a decreasing scratching resistance, which is a well-known behavior. Beyond a certain hydrogen content, a further increased hydrogenation causes a reproducible, slight increase of the scratching resistance. In order to explain this, the role of the friction coefficient will be discussed.
2:40 PM		VM+MI+AS-TuA-3 Ultrathin Overcoats For Magnetic Media: Is Hardness What We Are Looking For ? B. Marchon (IBM Almaden Research Center) As areal recording densities approach 20 Gigabit per square inch, the demand for ultrathin media overcoat (<5 nm) becomes more pressing. This talk will attempt to identify the various properties that are required to achieve good performance under increasingly severe mechanical and environmental conditions. In an attempt to bridge the process-performance gap, we will review the details of the head/disk interface system, and how the mechanical and chemical structure/properties can be optimized to achieve the required reliability. In particular, issues related to tribochemistry and interactions with the lubricant will be addressed, as well as a general discussion on what specific mechanical properties are important.
3:20 PM		VM+MI+AS-TuA-5 Air Bearing Collision Dynamics S.E. Stupp, R.J. Blanco, T. Riener, B.D. Strom (Quantum Corporation) A few years ago, a disk drive program encountered an unusual problem: drives built with one vendor's heads (vendor A) suffered from an excessive number of thermal asperity events (TAs); drives built with head's from another vendor (vendor B) did not have as many TAs, but they did have a number of crashes. Spinstand experiments confirmed that there was a significant difference in the response of the two vendor's air bearings to collision with the 100 nm high asperities found in these drives. For example, the fly height of vendor A's heads was essentially unchanged on contact with an asperity, while vendor B's heads exhibited a fly height change (these differences may explain the drive results). The underlying problem in the drive program was ultimately traced to particulate contamination and was corrected. However, the experiments raise an interesting question: Why is there a difference in the dynamic response of the two vendor's heads? In this work we present a systematic study of this problem, which we christen Air Bearing Collision Dynamics (ABCD). The asperity collision responses of several different air bearing designs (including full rail and island type) were studied by measuring the TA signal, the change in flying height, acoustic emission (AE), and laser Doppler vibrometry, in controlled experiments on a spinstand. Since a large enough asperity can cause any head to crash, the asperity size was modest (approximately equal to the fly height). In agreement with our earlier experiments, differences in the response of the different air bearings were found. In addition, the AE signals indicate that certain island type air bearing designs can undergo multiple head-disk contacts after the asperity has passed. These results are potentially concerning, because many head vendors are moving towards this type of air bearing design. Finally, in an attempt to understand the origin of the differences in the dynamic response of different air bearing designs, we report the results of numerical modeling of the asperity and air bearing designs.
4:00 PM		VM+MI+AS-TuA-7 Interaction of Fluoroalcohols and Fluoroethers with Various Types of Carbon Overcoats N. Shukla, A.J. Gellman (Carnegie Mellon University) This work is focussed on understanding the fundamentals of head-disk interface tribology at very low flying heights and higher spin rates. Since there will be room for only a single molecular monolayer of the lubricant on the disk surface at low flying heights we have studied the molecular level interaction of lubricants with carbon overcoats that protect the disk surface. We have modeled a most commonly used PFPE lubricant (Fomblin Zdol) using short chain model compounds and measured the desorption energy of these compounds on carbon films. The short chain model compounds used are 2,2,2 trifluoroethanol (CF₃CH₂OH) and perfluorodiethyl ether (CF₃CF₂OCF₂CF₃) which are representative of both the end group and the main chain of Fomblin Zdol. Temperature programmed desorption spectroscopy is used to measure the desorption energy of model compounds and also to understand the nature of the interaction of these short chain compounds with carbon overcoats. Initial results show that ethers interact with carbon overcoats through electron donation from the oxygen lone pair electron and the alcohols interact with carbon overcoats through hydrogen bonding. In addition we have studied the effect of various film compositions on the interaction of the lubricants in order to understand if the film composition has any effect on the nature of the bonding of the lubricant. The different types of overcoats used are hydrogenated, nitrogenated, diamond-like carbon and Ion beam sputtered overcoats. We have observed that by varying the percentage of hydrogen or nitrogen content in the film composition or by changing the carbon overcoat deposition conditions as in diamond like carbon overcoats or in an ion beam sputtered overcoat there is no significant change in the interaction of the lubricant with carbon overcoat. The alcohols however bond stronger than ethers on all overcoats, which is consistent with the structures, proposed by diffusion measurements.
4:20 PM		VM+MI+AS-TuA-8 Angle Resolved ESCA Methods: Molecular Conformation of Fluorocarbon Lubricant M.A. Karplus, D.J. Pocker (IBM-SSD) Simple but useful methods for interpreting angle-resolved ESCA data from real-world samples are presented. First is a model allowing thinly-covered and thickly-covered substrate. It can be usefully applied, even in a manual fashion, with common office spreadsheets. Next, a simple slab model, with the help of canned minimization routines, can bring out subtleties in overlayer structures. Even a deeply buried monatomic layer can be isolated. The following are presented as examples. Perfluoropolyether (Zdol) lubricant on hard disk carbon overcoat shows coexisting monolayer and multilayer regions, consistent with structures identified by surface energy¹ and ellipsometric surface diffusion² measurements. Next, layering within the lubricant shows significant perfluoropolyether backbone adjacent to the overcoat surface accompanied by a discernible excess of ether oxygen. The latter facts indicate that the inverted-U conformation sometimes sketched for bonded lubricants is an exaggeration, certainly for the system studied. ¹ G. W. Tyndall, R. J. Waltman, and D. J. Pocker, Langmuir 14, 7527 (1998). ² X. Ma, J. Gui, L. Smoliar, K. Grannen, B. Marchon, M. S. Jhon, C. L. Bauer, J. Chem. Phys. 110, 3129 (1999).
4:40 PM		VM+MI+AS-TuA-9 Airbearing Designs for High Density Recording A. Menon (Read-Rite Corp.)