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RESEARCH PAPERS

Design Optimization of Ultra-Low Flying Head-Disk Interfaces Using an Improved Elastic-Plastic Rough Surface Model

[+] Author and Article Information
Allison Y. Suh1

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Sung-Chang Lee2

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Andreas A. Polycarpou3

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801polycarp@uiuc.edu

1

Currently with Seagate Technology.

2

Currently with Samsung Information Systems America.

3

Corresponding author.

J. Tribol 128(4), 801-810 (Jun 09, 2006) (10 pages) doi:10.1115/1.2345399 History: Received June 13, 2005; Revised June 09, 2006

Abstract

Sub-$5nm$ flying head-disk interfaces (HDIs) designed to attain extremely high areal recording densities of the order of $Tbit∕in2$ are susceptible to strong adhesive forces, which can lead to subsequent contact, bouncing vibration, and high friction. Accurate prediction of the relevant interfacial forces can help ensure successful implementation of ultra-low flying HDIs. In this study, an improved rough surface model is developed to estimate the adhesive, contact, and friction forces as well as the mean contact pressure relevant to sub-$5nm$ HDIs. The improved model was applied to four different HDIs of varying roughness and contact conditions, and was compared to the sub-boundary lubrication rough surface model. It was found that the interfacial forces in HDIs undergoing primarily elastic-plastic and plastic contact are more accurately predicted with the improved model, while under predominantly elastic contact conditions, the two models give similar results. The improved model was then used to systematically investigate the effect of roughness parameters on the interfacial forces and mean contact pressure (response). The trends in the responses were investigated via a series of regression models using a full $33$ factorial design. It was found that the adhesive and net normal interfacial forces increase with increasing mean radius $R$ of asperities when the mean separation is small $(≈0.5nm)$, i.e., pseudo-contacting interface, but it increases primarily with increasing root-mean-square (rms) surface height roughness between 2 and $4nm$, i.e., pseudo-flying interface. Also, increasing rms roughness and decreasing $R$, increases the contact force and mean contact pressure, while the same design decreases the friction force. As the directions of optimization for minimizing the individual interfacial forces are not the same, simultaneous optimization is required for a successful ultra-low flying HDI design.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

Figure 8

Contour plots of F (in mN) as a function of σ and R for An=500μm2 at (a) h=0.5nm (fully contacting interface); (b) h=2nm (partially contacting interface for σ⩾0.7nm); (c) h=3nm (just contacting interface for σ=1nm); (d) h=5nm (fully flying interface)

Figure 9

Contour plots of Q (in mN) as a function of σ and R for An=500μm2 at (a) F=10mN; (b) F=15mN; (c) F=20mN; (d) F=25mN

Figure 10

Contour plots of Pm as a function of σ and R for An=500μm2 at (a) F=10mN; (b) F=15mN; (c) F=20mN; (d) F=30mN

Figure 1

Schematic of a HDI (a) during flying (Fs=adhesive force, P=contact force, Q=friction force, Fa=air-bearing force); (b) during contact; (c) equivalent rough surface in contact with a smooth plane in the presence of molecularly thin lubricant (h=mean surface height)

Figure 2

Typical slider air bearing surface (ABS)

Figure 3

AFM roughness of (a) disk 1; (b) disk 3; (c) slider ABS

Figure 4

Net normal interfacial force predictions with HDI parameters listed in Tables  12

Figure 5

Friction force predictions with HDI parameters listed in Tables  12

Figure 6

Mean contact pressure predictions with HDI parameters listed in Tables  12

Figure 7

Contour plots of Fs as a function of σ and R for An=500μm2 at (a) h=0.5nm (fully contacting interface); (b) h=2nm (partially contacting interface for σ⩾0.7nm); (c) h=3nm (just contacting interface for σ=1nm); (d) h=5nm (fully flying interface)

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