Air-Bearing Effects on Actuated Thermal Pole-Tip Protrusion for Hard Disk Drives

[+] Author and Article Information
Jia-Yang Juang, David B. Bogy

Computer Mechanics Laboratory, Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720

J. Tribol 129(3), 570-578 (Feb 27, 2007) (9 pages) doi:10.1115/1.2736456 History: Received November 10, 2006; Revised February 27, 2007

Flying height (FH) control sliders with thermal actuation have been introduced recently in commercial products for compensating the static FH loss and reducing the risk of head-disk contacts. In the research reported here, we investigated the effects of air-bearing surface (ABS) designs on the thermal actuation. We created a three-dimensional finite element model of an entire slider with a detailed read/write transducer structure and conducted thermal-structural coupled-field analysis using velocity slip and temperature jump boundary conditions to formulate the heat transfer across the head-disk interface when a slider flies over a spinning disk. An iteration procedure was used to obtain the equilibrium solutions. Four ABS designs with distinct features were simulated. We defined five measures of merit, including protrusion rate, actuation efficiency, power consumption, pressure peak, and temperature rise of the sensor to evaluate the performance of thermal actuation. It is found that the effect of the pressure is more significant than that of the FH on the heat conduction from the slider to the disk. The efficiencies of three conventional designs decrease as the FHs are continuously reduced. A new ABS design, called “Scorpion III,” is presented and demonstrates an overall enhancement, including virtually 100% efficiency with significantly less power consumption. Transient thermal analysis showed that it requires 12ms for the temperature to reach the steady-state values, and there is a trade-off between increasing the actuation bandwidth and decreasing the power consumption.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Finite-element model of a FH control slider with thermal actuation. The overcoat and photoresist are not shown for a clear view of the read/write transducer. The protective carbon overcoat on the ABS and the pole-tip recession are not considered.

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Figure 2

Four ABS designs used in this study (length: 1.25mm; width: 1.00mm). Different colors indicate different etching levels.

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Figure 3

Air pressure distributions of the ABS sliders. The scale displayed is normalized to ambient pressure: (p−pa)∕pa.

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Figure 4

Prototype of a fabricated Al2O3-TiC slider having an isolated center trailing pad with all relevant read/write elements. The dimension of the pad is 100μm by 30μm, which can also be increased to accommodate larger transducer designs.

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Figure 5

(a) Simulation of gap FH and minimum FH profiles of Scorpion III at sea level, 0m, and high altitude, 4500m; and (b) simulation of pitch and roll profiles of Scorpion III at sea level, 0m. The skew angle varies from −15.62deg to 7.22deg from the inner diameter to the outer diameter.

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Figure 6

Distributions of the interface thermal conductance on the air-bearing surfaces at a heating power of 20mW. Only part of the ABS that is close to the trailing edge is plotted. The distances of the write gap and the GMR sensor from the trailing edge are 33μm and 36.5μm, respectively.

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Figure 7

Distributions of the temperature rises on the ABSs at a heating power of 20mW

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Figure 8

Distributions of the heat flux on the ABSs at a heating power of 20mW

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Figure 9

Distributions of the A-PTP on the ABSs at a heating power of 20mW

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Figure 10

Comparison of actuated thermal protrusion profiles of the four air bearings along the centerline across the read/write element at a heating power of 20mW

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Figure 11

FH reductions as a function of heating power. The dashed lines are the linear projections, and the solid lines are quadratic fits to the data.

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Figure 12

Comparison of the A-PTP as a function of the heating power. The protrusion rates are about 0.19, 0.17, 0.21, and 0.34nm∕mW for CML-5nm, slider A, slider B, and Scorpion, respectively.

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Figure 13

Comparison of the efficiency as a function of the FH. The efficiencies of CML-5nm, slider A, and slider B monotonically decrease as the FHs are reduced by the thermal protrusions, and Scorpion demonstrates virtually 100% efficiency.

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Figure 14

Required heating power for reducing the FH

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Figure 15

Comparison of the peak pressures as functions of the FHs

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Figure 16

Temperature rises of the sensors when the FHs are reduced by applying a heating power

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Figure 17

Transient temperature changes of the flying sliders with a varying heating power. The power required for the first 1nm FH reduction for each of the ABSs was applied from 0 to 2.5ms and was turned off at 2.5ms.



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