Laser System Induced Protrusion Joanna Bechtel Dahl & Prof. - PowerPoint PPT Presentation

Static and Dynamic Slider Air Bearing Behavior in Heat Assisted Magnetic Recording under TFC and Laser System Induced Protrusion Joanna Bechtel Dahl & Prof. David Bogy Computer Mechanics Laboratory, UC Berkeley CML Sponsors’ Meeting January 27, 2014

Acknowledgements Thank you to the CML member companies for supporting this research. Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

HAMR HDI New thermal issues introduced by HAMR complicate HDI reliability. � Extreme temperatures: “Thermal modelling indicates that the NFT temperature may rise by several hundred degrees.” Challener et. al., Nature Photonics 3 (2009): 220-224. � Laser-induced Protrusion: “Several nanometers of protrusion may be possible during HAMR writing” in the recording head “around the area of the [magnetic] pole and optical spot due to heat from the [magnetic write] field and optical delivery”. Kryder et. al., Proc. IEEE 96 (2008): 1810-1835. Air Bearing Modeling: Predict HAMR slider flying characteristics under an active heater and laser. Does the hot NFT affect the flying attitude? Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Outline � Our HAMR slider design � Static simulations: Effect of NFT temperature � Air bearing dynamics due to NFT temperature change � Step response � Pulsed laser response Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Our HAMR Slider Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Our HAMR Slider /01&ABC&$D5($38&8)& *(#E&%$5)%*(3-&F(8?&& 93:.8& !)##$#&8)&+%(8$&=)<$&& G3#:$5(H$*&<)##$#& ;<$58%(5"<& '()*$#&ABJC&$D5($38?& "3*&5).:<(3-&<)##$#?& /01&*(##(:"8$#&IJKLJC& =)>$%& M<<&<)##$#&*(##(:"8$*& /)&*(##(:"4)3&(3&+@& 2"-3$45& 6$5)%*(3-& BJ&N+&& IJ&N+&& +",$-.(*$& JPB&N+&& IJJ&N+&& !"#$%&'()*$& /01& 7(8& QPBKRPB&N+&& BJ&N+&& OJ&N+&& IKL&N+&& M. Seigler et al., IEEE Trans. Magn. 44: 119-124, 2008. W. Challener et al., Nature Photonics 3: 220-224, 2009 B. Stipe et al,. Nature Photonics 4: 484-488, 2010. B. Xu et al., Jap. J. Appl. Phys ., 50: 09MA05, 2011. B. Xu et al., IEEE Trans. Magn . 48: 1789-1793, 2012. Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Our HAMR Slider � 843.5 µ m x 700 µ m � 5400 RPM � Radius 22.215 mm, skew 0.943˚ Centerline" Profiles" Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Air Bearing Equation Fukui and Kaneko’s equation: lubrication approximation + linearized Boltzmann equation � Traditional HDD: isothermal molecular gas lubrication equation $ ' σ ∂ ( PH ) ∂ P + ∂ ∂ X Λ 0 PH − PH 3 Q P ) = 0 & % ∂ X ( ∂ τ � HAMR HDD: full MGL equation that accounts for local air bearing properties * - , / T − PH 3 ∂ X + P 2 H 3 " PH % PH ∂ P ∂ T w σ ∂ ' + ∂ µ T Q P µ T 2 Q T = 0 ∂ X Λ 0 $ , / # T & ∂ X ∂ τ       , / + . Thermal Creep Λ 0 = 6 LU µ 0 " % T ≈ T ave = 1 T d + T s ' $ 2 S. Fukui and R. Kaneko, J. p 0 h 0 2 T 0 # & Tribology 110: 253-262, 1988. Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Iterative Static Solver: Base Cases An iterative static solver between the air bearing and thermo-mechanical deformation solvers is used to generate ABS temperature and deformation profiles to be interpolated in the dynamic simulation. Heat transfer coefficient Pressure force on ABS Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Assumptions � Disk thermal spot (25-nm FWHM) and deformation is too small to affect slider’s flying dynamics. � Thermal spot on ABS due to NFT is 3.6- µ m FWHM. � Ignore disk roughness. � Isolate the effect of the ABS temperature (NFT) on the slider’s flying dynamics. Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Static Results: Effect of NFT Temperature Within the air bearing solver… Case 1: Use non-isothermal air bearing equation and ABS temperature from finite element solution as boundary condition (RED) Case 2: Use isothermal air bearing equation and assume isothermal ABS at ambient temperature (BLUE) Protrusion is the same ABS Temperature ABS Protrusion 300 0 Non − isothermal ABS NFT location Isothermal ABS 250 ABS Temperature (C) ABS Protrusion (nm) 200 5 150 100 10 NFT location 50 Non − isothermal ABS Isothermal ABS 0 15 800 805 810 815 820 825 830 835 840 800 805 810 815 820 825 830 835 840 Slider Length Direction (um) Slider Length Direction (um) Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Static Results: Pressure Air bearing pressure at the trailing edge region is higher when the elevated ABS temperature (hot NFT) is included in the governing air bearing equation. Pressure difference near NFT Air Bearing Pressure at TE Region ( RED – BLUE ) MPa 5 354 Non − isothermal ABS NFT location 0.6 4.5 Isothermal ABS 353 4 Air Bearing Pressure (MPa) 0.5 Slider Width Direction (um) 352 3.5 NFT location 351 0.4 3 2.5 350 0.3 2 349 0.2 1.5 348 1 0.1 347 0.5 0 0 346 800 805 810 815 820 825 830 835 840 822 824 826 828 830 Slider Length Direction (um) Slider Length Direction (um) Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Static Results: Flying Height The higher pressure force at the trailing edge pitches the slider forward, thereby decreasing the minimum flying height. Flying height difference along the entire slider length Flying Height at TE Region ( RED – BLUE ) 14 0.3 NFT location NFT location 12 0.2 Flying Height Difference (nm) 10 Flying Height (nm) 0.1 8 0 6 − 0.1 4 − 0.2 LE TE 2 Non − isothermal ABS Isothermal ABS 0 − 0.3 800 805 810 815 820 825 830 835 840 0 100 200 300 400 500 600 700 800 Slider Length Direction (um) Slider Length Direction (um) Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

Dynamic Solver Input Files ABS Temperature Due to NFT 300 Non − isothermal ABS Isothermal ABS and TFC 250 ABS Temperature (C) Prescribed variation in time of peak 200 dT temperature change 150 � Step 100 NFT location � Pulsed: Laser-off condition when 50 pass over servo zone 0 800 805 810 815 820 825 830 835 840 � 2.6667 µ s laser-off (servo sector) Slider Length Direction (um) 0 � 41.778 µ s laser-on (data sector) NFT location ABS Protrusion (nm) TFC- and NFT-Induced Thermal 5 Protrusion Same constant protrusion profile for 10 duration of dynamic simulation for Non − isothermal ABS both ABS temperature cases Isothermal ABS 15 800 805 810 815 820 825 830 835 840 Slider Length Direction (um) Joanna B. Dahl, David B. Bogy January 27, 2014 Computer Mechanics Laboratory

420 419.7 Center of Total Pressure dT X Coordinate (um) Force on ABS dT = 0C 419.4 dT = 49C Step Case dT = 94C dT = 138C 419.1 dT = 183C 64 kHz – 1 st pitch mode 418.8 Center of ABS max temperature schematic 418.5 0.45 0.49 0.53 0.57 0.61 0.65 Time (ms) Pressure X 420 dT 419.7 Center of Total Pressure X Coordinate (um) Force on ABS dT = 0C 419.4 Pulsed Case dT = 49C dT = 94C dT = 138C 419.1 dT = 183C 418.8 ABS max temperature schematic 418.5 0.8 0.83 0.86 0.89 0.92 0.95 Time (ms)

73.25 64 kHz – 1 st pitch mode 73.05 dT dT = 0C Pitch (urad) 72.85 dT = 49C Step Case dT = 94C dT = 138C 72.65 dT = 183C 72.45 ABS max temperature schematic 72.25 Pitch 0.45 0.49 0.53 0.57 0.61 0.65 Time (ms) 73.25 73.05 dT dT = 0C Pitch (urad) 72.85 Pulsed Case dT = 49C dT = 94C dT = 138C 72.65 dT = 183C 72.45 ABS max temperature schematic 72.25 0.8 0.83 0.86 0.89 0.92 0.95 Time (ms)

1 0.7 Center of Total Pressure dT Y Coordinate (um) Force on ABS dT = 0C 0.4 Step Case dT = 49C dT = 94C dT = 138C 0.1 dT = 183C − 0.2 Center of ABS max temperature schematic − 0.5 0.45 0.49 0.53 0.57 0.61 0.65 Pressure Y Time (ms) 1 0.7 Center of Total Pressure dT Y Coordinate (um) Force on ABS dT = 0C 0.4 Pulsed Case dT = 49C dT = 94C dT = 138C 0.1 dT = 183C − 0.2 ABS max temperature schematic − 0.5 0.8 0.83 0.86 0.89 0.92 0.95 Time (ms)

2.5 2.3 dT dT = 0C 2.1 Roll (urad) Step Case dT = 49C dT = 94C dT = 138C 1.9 dT = 183C 1.7 ABS max temperature schematic Roll 1.5 0.45 0.49 0.53 0.57 0.61 0.65 Time (ms) 2.5 2.3 dT dT = 0C 2.1 Roll (urad) Pulsed Case dT = 49C dT = 94C dT = 138C 1.9 dT = 183C 1.7 ABS max temperature schematic 1.5 0.8 0.83 0.86 0.89 0.92 0.95 Time (ms)

1.8 1.64 Minimum Flying Height (nm) dT dT = 0C 1.48 dT = 49C Step Case dT = 94C dT = 138C 1.32 dT = 183C 1.16 Minimum ABS max temperature schematic 1 Flying 0.45 0.49 0.53 0.57 0.61 0.65 Time (ms) Height 1.8 1.64 Minimum Flying Height (nm) dT = 0C 1.48 dT = 49C Pulsed Case dT = 94C dT = 138C 1.32 dT = 183C dT 1.16 ABS max temperature schematic 1 0.8 0.83 0.86 0.89 0.92 0.95 Time (ms)