Friction and wear studies of silicon in sliding contact with thin-film magnetic rigid disks
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Silicon is an attractive material for the construction of read/write head sliders in magnetic recording applications from the viewpoints of ease of miniaturization and low fabrication cost. In the present investigation we have studied the friction and wear behavior of single-crystal, polycrystalline, ion-implanted, thermally oxidized (wet and dry), and plasma-enhanced chemical vapor deposition (PECVD) oxide-coated silicon pins while sliding against lubricated and unlubricated thin-film disks. For comparison, tests have also been conducted with Al 2 O 3 -TiC and Mn-Zn ferrite pins which are currently used as slider materials. With single-crystal silicon the rise in the coefficient of friction with sliding cycles is faster compared to Al 2 O 3 -TiC and Mn-Zn ferrite pins. In each case, the rise in friction is associated with the burnishing of the disk surface and transfer of amorphous carbon and lubricant (in the case of lubricated disks) from the disk to the pin. Thermally oxidized (under dry oxygen conditions) single-crystal silicon and PECVD oxide-coated single-crystal silicon exhibit excellent tribological characteristics while sliding against lubricated disks, and we believe this is attributable to the chemical passivity of the oxide coating. In dry nitrogen, the coefficient of friction for single-crystal silicon sliding against lubricated disks behaves differently than in air, decreasing from an initial value of 0.2 to less than 0.05 within 5000 cycles of sliding. We believe that silicon/thin-film disk interface friction and wear is governed by the uniformity and tenacity of the amorphous carbon transfer film and oxygen-enhanced fracture of silicon.
I. INTRODUCTION Conventional hard-disk magnetic storage systems employ the relative motion of a rotating hard disk against a stationary read/write magnetic head.1 The average interface contact pressure at the head-disk interface is typically around 7-14 kPa, and the operating speed is in the range of 10-60 m/s. Depending on the drive system, the head starts to fly and takes off the disk surface at speeds ranging from 1 to 10 m/s. Typically, under steady-state operating conditions, a hydrodynamic air film about 0.1-0.3 /mm thick is formed between the head and the disk, thereby preventing direct contact between the two. Physical contact between the head and the disk occurs below the takeoff speed during the starting and stopping of the disk drive and sometimes at isolated asperities during flying. The need for increasing the storage density has necessitated research into systems with ultralow flying gaps (typically less than 0.1 fim) and ultrasmooth disk and head surfaces. The design of systems with low flying heights and ultrasmooth surfaces in turn requires a thorough understanding of the tribology of the head-disk interface. A critical need exists for the development of head-slider materials and disk surfaces with low friction and wear characteristics that can be produced economically. J. Mater. Res., Vol. 8, No. 7, Jul 1993
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