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UNIVERSITY of CALIFORNIA, SAN DIEGO Numerical And UNIVERSITY OF CALIFORNIA, SAN DIEGO Numerical and Experimental Investigations of the Head/Disk Interface A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Engineering Sciences (Mechanical Engineering) by Maik Duwensee Committee in charge: Professor Frank E. Talke, Chair Professor David J. Benson Professor Thomas Bewley Professor Eric Fullerton Professor Jack Keil Wolf 2007 Copyright Maik Duwensee, 2007 All rights reserved. The dissertation of Maik Duwensee is approved, and it is acceptable in quality and form for publi- cation on microfilm: Chair University of California, San Diego 2007 iii to my parents B¨arbel† and Dieter Duwensee iv TABLE OF CONTENTS Signature Page . iii Dedication . iv Table of Contents . v List of Figures . viii List of Tables . xii Acknowledgements . xiii Vita and Publications . xvi Abstract of the Dissertation . xviii 1 Introduction . 1 1.1 History of Computer Hard Disk Drives . 1 1.2 Areal Storage Density . 5 1.3 Current and Future Technologies for Areal Storage Density Increase 9 1.3.1 Perpendicular Magnetic Recording . 9 1.3.2 Heat Assisted Magnetic Recording . 11 1.3.3 Patterned Media Technologies . 14 1.4 Principles of Magnetic Recording . 17 1.4.1 Magnetic Hysteresis . 17 1.4.2 Evolution of Magnetic Read/Write Heads . 20 1.4.3 Write Process . 22 1.4.4 Read-back Process . 23 1.4.5 Magnetic Spacing . 28 1.5 Mechanical Components of a Disk Drive . 32 1.5.1 Air Bearing Sliders . 33 1.5.2 Suspensions . 41 1.5.3 Spindle Motor Bearings . 47 1.5.4 Magnetic Disks . 49 1.6 Head/Disk Interface . 51 1.7 Organization of the Thesis . 55 Bibliography . 57 v 2 Voltage Pulsing for Localized Clearance Measurement . 61 2.1 Introduction . 62 2.2 Experimental Setup . 63 2.3 Experimental Results . 65 2.4 Discussion and Conclusions . 72 2.5 Acknowledgement . 73 Bibliography . 75 3 Disk Mapping . 76 3.1 Introduction . 77 3.2 Experimental Setup . 78 3.3 Experimental Results . 79 3.4 Summary . 82 3.5 Acknowledgement . 83 Bibliography . 84 4 Hydrodynamic Lubrication of the Head/Disk Interface . 85 4.1 The Reynolds Equation . 86 4.2 Slip Flow Correction for Low Spacing . 92 4.3 The Finite Element Formulation of the Reynolds Equation . 97 4.4 Slider Equilibrium Equations . 105 Bibliography . 110 5 Air Bearing Simulation of Discrete Track Head/Disk Interfaces . 113 5.1 Introduction . 114 5.2 Mathematical Modelling . 117 5.3 Simulation Model . 118 5.4 Simulation Results and Discussion . 121 5.5 Summary and Conclusions . 129 5.6 Acknowledgement . 130 Bibliography . 132 6 The Direct Simulation Monte Carlo Method . 133 6.1 Introduction . 133 6.2 DSMC Simulation Algorithm . 137 6.2.1 Initialization . 140 vi 6.2.2 Streaming and Boundary Conditions . 143 6.2.3 Collisions . 149 6.2.4 Sampling . 154 6.3 Limitations of the DSMC method . 156 Bibliography . 158 7 Simulation of Rarefied Gas Flow in Nano Channels . 160 7.1 Introduction . 160 7.2 Simulation Model . 161 7.3 DSMC Simulation Results . 165 7.4 Discussion . 172 7.5 Acknowledgement . 175 Bibliography . 176 8 Summary and Conclusions . 177 A Supplemental Information for Chapter 1 . 182 A.1 Surface Roughness Characterization . 182 A.2 Van der Waals Forces of the Head/Disk Interface . 183 A.3 Experimental Determination of the Hamaker Constant . 186 B Supplemental Information for Chapter 2 and 3 . 189 B.1 Laser Doppler Vibrometry . 189 B.2 Acoustic Emission . 192 C Supplemental Calculations for Chapter 4 . 194 C.1 Order of Magnitude Analysis . 194 C.2 Integration of the Continuity Equation . 198 C.3 Element Stiffness Matrix . 199 C.4 Simultaneous Newton-Raphson Scheme for Steady State Slider Air Bearing Simulations . 208 Bibliography . 211 vii LIST OF FIGURES Figure 1.1: Schematic of notched-disk memory as suggested by Rabi- now [32] (source [32]) . 2 Figure 1.2: Random Access Memory Accounting Machine (RAMAC) (pic- ture source [38]) . 4 Figure 1.3: Development of areal storage density versus time . 6 Figure 1.4: Schematic longitudinal magnetic recording (source [13]) . 10 Figure 1.5: Schematic perpendicular magnetic recording (source [13]) . 11 Figure 1.6: Schematic of write process in heat assisted magnetic record- ing (HAMR) . 12 Figure 1.7: Schematic of heat assisted magnetic recording (HAMR) (source [37]) . 14 Figure 1.8: Schematic of discrete track recording (DTR) . 15 Figure 1.9: Schematic of bit patterned media (BPM) . 16 Figure 1.10: Magnetic hysteresis curve . 19 Figure 1.11: Evolution of magnetic read/write heads (source [13]) . 21 Figure 1.12: Schematic of magnetic write process . 22 Figure 1.13: Schematic of inductive read back process . 23 Figure 1.14: Schematic of read-back signal for a given magnetization pattern 24 Figure 1.15: Anisotropic magnetoresistance of a ferromagnetic material . 25 Figure 1.16: Schematic of read-back process using a magnetoresistive head 26 Figure 1.17: Definition of symbols for read-back signal analysis . 29 Figure 1.18: Photograph of a modern hard disk drive, with major com- ponents annotated (source: [37]) . 32 Figure 1.19: Radial positioning of slider over disk surface by voice coil motor driven actuator arm (source: [37]) . 33 Figure 1.20: Development of flying height versus time . 34 Figure 1.21: Evolution of air bearing slider design (source: [13]) . 35 Figure 1.22: Definition of skew angle . 37 Figure 1.23: Schematic of sub-ambient air bearing slider design . 39 Figure 1.24: Schematic of load/unload mechanism (source: [13, 42]) . 40 Figure 1.25: Schematic head-gimbal-suspension assembly . 42 Figure 1.26: Photograph of electrical connections for read/write element (source [16]) . 42 Figure 1.27: Photograph of typical suspension with design features anno- tated (source [16]) . 44 Figure 1.28: Photograph of suspension design with integrated copper con- ductors (source [16]) . 45 Figure 1.29: Evolution of suspension design (source [16]) . 46 viii Figure 1.30: Schematic of ball bearing spindle motor (source [6, 13]) . 47 Figure 1.31: Schematic of fluid dynamic bearing (FDB) spindle motor (source [6, 13]) . 48 Figure 1.32: Schematic of layered structure of magnetic disk . 49 Figure 1.33: Schematic of a typical disk topography profile for one revo- lution . 52 Figure 1.34: Definition of head/disk interface spacing parameters . 53 Figure 1.35: Schematic of the multilayered structure of the head/disk in- terface . 54 Figure 2.1: Experimental setup for localized clearance measurement us- ing voltage pulsing . 64 Figure 2.2: Slider displacement (a) and applied voltage (b) versus time; rotational speed: 5krpm ........................ 65 Figure.
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