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TECHNICAL PAPERS

Effects of Molecularly Thin Liquid Lubricant Films on Slider Hysteresis Behavior in Hard Disk Drives

[+] Author and Article Information
Norio Tagawa1

Department of Mechanical Engineering, Faculty of Engineering, High Technology Research Center, Kansai University, Suita, Osaka 564-8680, Japantagawa@ipcku.kansai-u.ac.jp

Atsunobu Mori

Department of Mechanical Engineering, Faculty of Engineering, Kansai University, Suita, Osaka 564-8680, Japan

Ken Senoue

 Exedy Corporation, Neyagawa, Osaka 572-8570, Japan

1

Corresponding author.

J. Tribol 129(3), 579-585 (Jan 10, 2007) (7 pages) doi:10.1115/1.2736448 History: Received April 07, 2006; Revised January 10, 2007

In order to achieve a magnetic recording density of 1Tbin2, the spacing is expected to be less than 23nm. However, a critical issue in achieving such an ultralow spacing is the dynamic instability of the head disk interface (HDI). That is, the experimentally observed hysteresis of fly sliders. The phenomenon of slider hysteresis has two features: slider touchdown and slider takeoff. The goal of this research is to experimentally clarify the effects of the lubricant bonded ratio as well as the lubricant film thickness on slider hysteresis behavior in detail. It also aims to determine the contributing factors. In this study, the difference in the touchdown and takeoff velocities was monitored by varying the lubricant bonded ratio and lubricant film thickness of the disks. Furthermore, the correlation between the observed phenomenon and the variation in the experimental parameters was investigated. The results showed that the touchdown velocities were almost independent of the lubricant bonded ratio, while the takeoff velocities were greater for a lubricant with a higher bonded ratio. These results were obtained for a constant lubricant film thickness of around one monolayer. Therefore, the slider hysteresis was greater for a lubricant with a higher bonded ratio. With regard to the effect of lubricant film thickness, it was observed that the touchdown and takeoff velocities were greater for thinner lubricants. These results for the effect of lubricant film thickness are very similar to those obtained by Ambekar, Gupta, and Bogy (2005, ASME J. Tribol., 127(3), pp. 530–536). However, the slider hysteresis was greater for thicker lubricants. Considering these experimental results as well as the experimental data for the effect of the surface roughness of a disk on the slider hysteresis obtained by (Tani (2006, J. Appl. Phys. , 99(8), pp. 08N104-1–08N104-3), it was suggested that the variation in the touchdown velocity is due to a variation in the intermolecular forces. Furthermore, it was suggested that the variation in the takeoff velocity is caused by a variation in the friction forces between the slider and disk surface. This occurs because the takeoff velocity was greater for a lubricant with a higher bonded ratio or a thinner lubricant, which only has a small fraction of free mobile lubricant. The results predicted by the simulations are consistent with those observed experimentally. In addition, a design guideline for next-generation HDI, with small touchdown and takeoff velocities, resulting in small slider hysteresis, is discussed in detail in this paper.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of slider fly height hysteresis

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Figure 2

Experimental setup and measurement system

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Figure 3

Test slider mechanism and air-bearing surface

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Figure 4

LDV rms values versus disk velocity as a parameter of lubricant film thickness

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Figure 5

Lubricant film thickness profile of the test disk

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Figure 6

LDV rms values versus disk velocity as a parameter of lubricant film thickness

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Figure 7

LDV rms values versus disk velocity as a parameter of lubricant bonded ratio

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Figure 8

Effect of lubricant bonded ratio on slider hysteresis

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Figure 9

Lubricant film thickness profile (bonded ratio: 14%)

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Figure 10

Lubricant film thickness profile (bonded ratio: 37%)

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Figure 11

Lubricant film thickness profile (bonded ratio: 52%)

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Figure 12

Multilayer model for calculating intermolecular forces

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Figure 13

Computed van der Waals pressure

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