Research Papers: Micro-Nano Tribology

Characterization of Thermally Actuated Pole Tip Protrusion for Head-Media Spacing Adjustment in Hard Disk Drives

[+] Author and Article Information
Sung-Chang Lee

 Samsung Information Systems America, 75 West Plumeria Drive, San Jose, CA 95134sungc.lee@samsung.com

Brian D. Strom

 Apple Inc., 1 Infinite Loop, MS5-Q, Cupertino, CA 95014strom@apple.com

J. Tribol 130(2), 022001 (Mar 03, 2008) (6 pages) doi:10.1115/1.2842248 History: Received August 29, 2007; Revised December 07, 2007; Published March 03, 2008

The effect of thermomechanically actuated pole tip protrusion on adhesive forces is characterized through model and experiment. The roughness of a thermomechanically actuated region is characterized by atomic force microscopy. Using the extracted roughness parameters and estimated apparent area associated with thermal actuation, the intermolecular forces at the head-disk interface (HDI) are calculated using the ISBL (improved sub-boundary lubrication) code. Both roughness and nominal area of contact are found to be significant factors determining adhesive forces. The adhesive forces for various HDI designs—including thermal actuation—are also characterized experimentally in situ using commercial hard disk drive samples. The experimental results are found to be consistent with the model calculations and imply certain advantages for thermally actuated HDI designs. However, the experiments also raise concerns regarding the field application of the technology.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Thermal pole tip actuation and corresponding HMS change. Due to the higher peak of air-bearing pressure on the pole tip protruded area, the pitch angle can decrease.

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Figure 2

(a) 3D AFM image of the thermally actuated pole tip area when 62.5mW was applied and (b) optical microscope image of the slider

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Figure 3

Trends of roughness parameters of the thermally actuated pole tip area with applied power (σ, rms roughness; R, mean asperity radius)

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Figure 4

Adhesion force predictions using the ISBL model with and without thermal actuation. Contact initiates at zero minimum spacing.

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Figure 5

Experimental setup to monitor adjusted HMS

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Figure 6

Contact hysteresis due to thermal actuation (ambient condition): (a) read-back signal amplitude while increasing and decreasing thermal actuation; (b) corresponding standard amplitude variation

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Figure 7

Altitude contact hysteresis measurement with and without DLC pads. Contact hysteresis (=takeoffpressure−touch-downpressure) was greatly reduced with DLC pads (less nominal area of contact)

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Figure 8

Altitude contact hysteresis measurements. ((a) and (b)) Without thermal actuation. ((c) and (d)) With thermal actuation (initial adjusted FH=3.7nm). The height of DLC pads was exaggerated.



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