Simulation of Air Bearing Pressure on Discrete TrackRecording Media

W. Zhou, B. Liu, S. Yu, and W. Hua

II MODELLING

Abstract-This paper investigates the influence of A femto-sized slider with 3.5 nm FH, Panda III,the grooves of discrete track recording media on a developed by DSI, is used in the simulationsmall pad of a femto-sized slider based on DSI studies. Figure 1(a) shows the geometry of thedeveloped simulator ABSolution. The simulation ABS. To avoid the problem on meshing the wholestudy shows that the total force on the pad will

A

decrease as groove depth increases, and this relation ABS surface using ultra fine grid, we add a smallcan be well predicted by using average thin film 15imx30imx5nm rectangular pad on the originaltheory to approximate the exact discrete track trailing rail. The mesh size on small pad is fixeddistribution on the media. around 55nmx45nm to capture the groove

Index Terms-patterned media, discrete track influence, and a non-uniform coarse mesh is used

recording, air bearing slider in meshing other ABS areas. This meshingarrangement is based on the assumption that a veryfine mesh is only needed in the areas where high

I. INTRODUCTION pressure and low spacing are expected.It is believed that patterned media recording will

be used in the next generation hard disk drive The parameters for DTR media in the(HDD) for the higher areal density above simulation is chosen as: groove width=500nm,

2 groove pitch=1000nm, and the groove depth isITbit/in Currently, there are two types of varied from zero to six nanometer.proposed patterned media. One is called bitpatterned media (BPM), the other is Discrete The simulation test is done by fixing flyingTracking Recording (DTR). Slider flying over attitude at lOnm of nominal flying height, 100pradthese media will have different flying behavior of pitch angle and Oprad of roll angle. The pressurefrom the traditional smooth media [1]. For discrete distribution on the entire air bearing surface is

Tracking Recording media, the existing ridges and obtained and the total force on the small pad is alsocalculated by integrating pressure over its area.grooves on the media will affect pressure

distribution on the slider air bearing surface (ABS),and thus affect slider flying performance. III. SIMULATION RESULTS

This paper investigates the effect of discrete Figure 2 compares pressure profiles on slidertracks on a small protrusion trailing pad based on ABS and small trailing pad at the groove depth ofDSI developed air bearing simulator called Onm, 2nm and 5nm respectively. The peak pressureABSolution. This simulator employs finite element is built near the trailing edge of small pad andmethod, adaptive meshing technique and becomes smaller as the groove depth increases.unsymmetric-pattern multifrontal method to The pressure stripes which appear on the small padimprove its accuracy, stability and speed. A dense are mainly induced by the ridges and grooves overgrid size 500xlOOO is used to capture the details of the DTR media. And they show little effects on thegrooves over the media. The simulation results ABS other regions with higher spacing. Thisshow that the total forces on the small trailing pad verifies our defined mesh system to be acceptabledecrease as the groove depth increase from zero to for our simulation case. Figure 3 shows thesix nanometers. And this trend can be well variation of total force on small pad with theapproximated by using averaged thin film model. groove depth. It's found that the force will drop

as the groove depth increase. This relation can bewell predicted by using the average thin filmtheory [2],[3], which calculates the efficient

MaqnusQcript receivedl Augusit '31 2)006.W.~ ~ ~ 'Zhui.ihDt trg nsiue igpr,170 clearance based on the arithmetically averaged film

(phone: 65-6874-8623; fax: 65-6777-2406; e-mail: clearance and the harmonically averaged clearance.zhou_weidong@dsi.a-star.edu.sg). This method also provides better accuracy than the

B. Liu is with Data Storage Institute, Singapore, 117608. empirical equation used by Duwensee et al. [1].S. Yu is with Data Storage Institute, Singapore, 117608.W. Hua is with Data Storage Institute, Singapore, 117608.

REFERENCES roughness in the slip flow regime: The approximate methodand confirmation experiements," Trans. ASME, J. of

[1] M. Duwensee, S. Suzuki, J. Lin, D. Wachenschwanz and Tribology, vol. 111, pp. 495-503, 1989.F. E. Talke, "Air bearing simulation of discrete track recording [3] W. Hua and B. Liu, "Mechanism Studies of the Multiplemedia", Intermag Conference, San Diego, USA, 2006, Be-05. Flying States of the Air Bearing Slider," Tribology[2] Y. Mitsuya, T. Ohkubo, and H. Ota, "Averaged Reynolds International, vol. 39, pp. 649-656, 2006.equation extended to gas lubrication possessing surface

m~

< 1 ~~~~~~~Fg1- - -AB emtyadnnuiomms

:s~~~~~I [ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

r~~~II

(a) groove depthmm(b)roovedp(c) groove depth=Snm

F.2 r p

I~ ~~~~~~~FgI ABSgoer1n nnuiommsr~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~..tWW_~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~................00~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.........................

t~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~H

1095UE+002~~~~ ~~~~~~~~~~~~~ .... +03 ....eE

1.

.l............... .........................................Q.l.... .n E-

(a)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. grov dethOn grov det=n(c)... ....pth......5..m

. 2 Pr ss r .rfl ....eAB.n. m ll t aln.ada aiu g o v e t

C..

° 0.2 ... ...... . .:

04. . . .

_" .2 .............................................L-L 0.1 .

&1 2 3 4 6GrooVe depth (hnm)

Fig.3 The pad force changes vs groove depth