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

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

Acknowledgements

Thank you to the CML member companies for supporting this research.

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

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 Computer Mechanics Laboratory January 27, 2014

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 Computer Mechanics Laboratory January 27, 2014

Our HAMR Slider

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

Our HAMR Slider

!"#$%&'()*$& +",$-.(*$& /01& 2"-3$45& 6$5)%*(3-& 7(8&

93:.8& ;<$58%(5"<& =)>$%& !)##$#&8)&+%(8$&=)<$&& "3*&5).:<(3-&<)##$#?& /)&*(##(:"4)3&(3&+@& /01&ABC&$D5($38&8)& *(#E&%$5)%*(3-&F(8?&& G3#:$5(H$*&<)##$#& /01&*(##(:"8$#&IJKLJC& '()*$#&ABJC&$D5($38?& M<<&<)##$#&*(##(:"8$*&

IJJ&N+&& BJ&N+&& BJ&N+&& IJ&N+&& OJ&N+&& IKL&N+&& JPB&N+&& QPBKRPB&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 Computer Mechanics Laboratory January 27, 2014

Our HAMR Slider

Centerline" Profiles"

843.5 µm x 700 µm 5400 RPM Radius 22.215 mm,

skew 0.943˚

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

Air Bearing Equation

Fukui and Kaneko’s equation: lubrication approximation + linearized Boltzmann equation

Traditional HDD: isothermal molecular gas lubrication equation HAMR HDD: full MGL equation that accounts for local air

bearing properties

σ ∂(PH) ∂τ + ∂ ∂X Λ0PH − PH 3QP ∂P ∂X $ % & ' ( )= 0

T ≈ Tave = 1 2 Td +Ts T0 " # $ % & '

Λ0 = 6LUµ0 p0h0

2

• S. Fukui and R. Kaneko, J.

Tribology 110: 253-262, 1988.

σ ∂ ∂τ PH T " # $ % & '+ ∂ ∂X Λ0 PH T − PH 3 µT QP ∂P ∂X + P2H 3 µT 2 QT ∂Tw ∂X       * + , , ,

• .

/ / / = 0

Thermal Creep

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

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 Computer Mechanics Laboratory January 27, 2014

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-µm

FWHM.

Ignore disk roughness.

Isolate the effect of the ABS temperature (NFT) on the slider’s flying dynamics.

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

Static Results: Effect of NFT Temperature

800 805 810 815 820 825 830 835 840 50 100 150 200 250 300 Slider Length Direction (um) ABS Temperature (C) Non−isothermal ABS Isothermal ABS

NFT location

800 805 810 815 820 825 830 835 840 5 10 15 Slider Length Direction (um) ABS Protrusion (nm) Non−isothermal ABS Isothermal ABS

NFT location

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

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

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.

800 805 810 815 820 825 830 835 840 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Slider Length Direction (um) Air Bearing Pressure (MPa) Non−isothermal ABS Isothermal ABS

NFT location

Slider Length Direction (um) Slider Width Direction (um) 822 824 826 828 830 346 347 348 349 350 351 352 353 354 0.1 0.2 0.3 0.4 0.5 0.6 MPa NFT location

Air Bearing Pressure at TE Region Pressure difference near NFT (RED – BLUE)

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

Static Results: Flying Height

The higher pressure force at the trailing edge pitches the slider forward, thereby decreasing the minimum flying height.

Flying Height at TE Region Flying height difference along the entire slider length (RED – BLUE)

800 805 810 815 820 825 830 835 840 2 4 6 8 10 12 14 Slider Length Direction (um) Flying Height (nm) Non−isothermal ABS Isothermal ABS

NFT location

100 200 300 400 500 600 700 800 −0.3 −0.2 −0.1 0.1 0.2 0.3 Slider Length Direction (um) Flying Height Difference (nm)

NFT location

LE TE

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

800 805 810 815 820 825 830 835 840 50 100 150 200 250 300 Slider Length Direction (um) ABS Temperature (C) Non−isothermal ABS Isothermal ABS

NFT location

Dynamic Solver Input Files

800 805 810 815 820 825 830 835 840 5 10 15 Slider Length Direction (um) ABS Protrusion (nm) Non−isothermal ABS Isothermal ABS

NFT location

dT

ABS Temperature Due to NFT and TFC Prescribed variation in time of peak temperature change

Step Pulsed: Laser-off condition when

pass over servo zone

2.6667 µs laser-off (servo sector) 41.778 µs laser-on (data sector)

TFC- and NFT-Induced Thermal Protrusion Same constant protrusion profile for duration of dynamic simulation for both ABS temperature cases

Center of Pressure X

Step Case Pulsed Case

0.45 0.49 0.53 0.57 0.61 0.65 418.5 418.8 419.1 419.4 419.7 420 Time (ms) Center of Total Pressure Force on ABS X Coordinate (um) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

0.8 0.83 0.86 0.89 0.92 0.95 418.5 418.8 419.1 419.4 419.7 420 Time (ms) Center of Total Pressure Force on ABS X Coordinate (um) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

64 kHz – 1st pitch mode

Pitch

Step Case Pulsed Case

0.45 0.49 0.53 0.57 0.61 0.65 72.25 72.45 72.65 72.85 73.05 73.25 Time (ms) Pitch (urad) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

0.8 0.83 0.86 0.89 0.92 0.95 72.25 72.45 72.65 72.85 73.05 73.25 Time (ms) Pitch (urad) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

64 kHz – 1st pitch mode

Center of Pressure Y

Step Case Pulsed Case

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

dT

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

dT

Roll

Step Case Pulsed Case

0.45 0.49 0.53 0.57 0.61 0.65 1.5 1.7 1.9 2.1 2.3 2.5 Time (ms) Roll (urad) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

0.8 0.83 0.86 0.89 0.92 0.95 1.5 1.7 1.9 2.1 2.3 2.5 Time (ms) Roll (urad) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

Minimum Flying Height

Step Case Pulsed Case

0.45 0.49 0.53 0.57 0.61 0.65 1 1.16 1.32 1.48 1.64 1.8 Time (ms) Minimum Flying Height (nm) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

0.8 0.83 0.86 0.89 0.92 0.95 1 1.16 1.32 1.48 1.64 1.8 Time (ms) Minimum Flying Height (nm) dT = 0C dT = 49C dT = 94C dT = 138C dT = 183C ABS max temperature schematic

dT

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

Summary

The non-isothermal air bearing equation predicts

a higher pressure at the hot NFT region compared with the isothermal air bearing equation.

NFT hot temperature is a disturbance to the air

bearing system: A change in NFT temperature induces the high pressure force at the trailing edge that excites the first pitch mode of the slider.

Appendix

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

dynamics.def

CML Version 4.039 DYNAMICS.DEF **********************Problem Definition******************* xl(m) yl(/xl) xg(/xl) yg(/xl) zg(/xl) halt 0.0008435 0.829875 0.74096 0 0.17783 0 f0(kg) xf0(/xl) yf0(/xl) amz aip air 0.0025 0.5 0 1.62E-006 6.15E-013 4.61E-013 rpm dt(s) tf(s) ra ra_if ra_of 5400 1E-007 0.001 0.022215 0.005 0.06 ************************Suspension************************* iact xact(m) dact vact ske(deg) 1 0.038 0 0 0.943 isusp nmodes ncg alfa beta 0 0 0 0 1E-005 skz skp skr scz scp scr 30 1.745E-5 1.745E-5 4.73E-5 2.82E-10 3.42E-10 psa rsa 0 0 ******************Initial Flying Condition***************** hm(m) hp(rad) hr(rad) vz(m/s) vp(rad/s) vr(rad/s) 13.73E-9 73.12E-6 2.07E-6 0 0 0 *******************Solution Control************************ iqpo akmax emax idisc icreep icheby 5 1E-008 0.0005 1 1 1 ********************Grid Control*************************** iadapt isymmetry ioldgrid nx ny nsx nsy 0 0 0 865 561 1 1 difmax decay ipmax 60 60 0 ********************Intermolecular Forces********************** imfmode ConstantA ConstantB elecpot 1 1E-19 1E-76 0 ********************Asperity Contact********************** icmod ey ydst pratio frcoe 1 1.1159E+11 1E+012 0.3 0.3 ncz sikm(m) ceta(/m/m) rasper(m) rcts(m) rcte(m) glidh(m) ***************************Shock********************************** useshock normal pitch roll tstart tend 0 0 0 0 0 0 ***********************Additional Parameters******************* p0(pa) al(m) vis(nsm-2) temperature 1.0135E+005 6.7100E-008 1.8600E-005 25 init_disp_x init_disp_y init_disp_yaw 0.0000E+000 0.0000E+000 0.0000E+000 init_vel_x init_vel_y init_vel_yaw 0.0000E+000 0.0000E+000 0.0000E+000 yaw_inertia num_susp_nodes slider_node nairflow 2.3400E-012 6 3 0 damping_a frequency_a damping_b frequency_b 5.000000 10.000000 5.000000 50000.000000 ***********************End of Input Data*******************

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

Ts, UDG Interpolation

Ti, j(t) = T base

i, j × A(t)exp − (xi − x0)2

2σ 2

x

− (yj − y0)2 2σ 2

y

# $ % % & ' ( ( (x0, y0) peak location