Magnetic Nanotechnology and Metrology Needs in Magnetic Recording

Transcription

1 Perpendicular Media Heat Assisted Magnetic Recording Bit Patterned Media? Self Organized Arrays Magnetic Nanotechnology and Metrology Needs in Magnetic Recording Dieter Weller Seagate Research, Pittsburgh NNI Workshop, Gaithersburg, MD, January 27, 2004

2 Magnetic Layer AlMg Research Topics in the area of Magnetic Recording Technologies 2 mm Slider Seagate Barracuda ATA II Disk Recording Head A PFPE 5-15A a-ch x A 1mm Actuator Head Head Dieter Weller Page 2 Heads Media Mechanical Integration Servo Channel Tribology Systems Integration Theory, Modeling

3 Commercial products: 70 Gbits/in 2, GB/Platter Areal Density Progress 1 Tbit/in Gbit/in 2 Demonstration ~ 170 Gbit/in 2 10 years Research frontier: 1 Tbits/in Gbit/in 2 1 Mbit/in 2 2 kbit/in 2 25 years Lab Demos Products Year >10 7 increase Dieter Weller Page 3

4 GMR Read Sensor Inductive Write Element a Magnetic Recording Challenge SNR ~ 10 log ( ) SNR 1/ D* δ W N S S N N S S N N S S N N S σ B j a Recording Medium D* W ; σ j B 10% Transition position jitter dominated noise 1000 d D* = 8-10 nm Thermal Stability K u V/k B T>50 Gbit/in nm x 194 nm 10nm 64nm Writeability H 0 =K u /M S 2005?? The achievable areal density is limited by trade-offs between SNR, Thermal Stability and Writeability. Trends: Smaller Grains, higher Hc, higher recording speeds; better field sensors; Dieter Weller Page 4

5 Perpendicular Recording: Hysteresis Requirements MOKE Hn S=1 Return pole field Write pole field 1.0 P1 P2 FH H C M perp / M S H C = 13.1 koe H K = 23.6 koe M S = 750 emu/cm 3 COC IL MAG HSS HSS M A K U = 8.85 x 10 6 erg/cm 3 H r = -5.2 koe S = 1, α = 1.75 T = 300K SUL H [ koe ] glass Characterization Needs: Disk motion Magnetic Moment, MAG Loop in presence of SUL, Anisotropy, Internal Field Corrections (slope), switching field distributions (SFD), Anisotropy dispersions Dieter Weller Page 5

6 1Tbit/in 2 media designs Key magnetics and structural media parameters Carbon overcoat (COC) Magnetic layer (Mag) Interlayer (IL) Soft underlayer (SUL) Bertram Wood Victora Williams Mallary unit year Areal Density Tbit/in2 H k koe H 0 (1ns) koe H c (VSM) 8 koe M r emu/cc Mag thickness nm IL thickness nm Grain diameter nm Lake Arrowhead Dieter Weller Dec. 9, 2002 Seagate Research Page 6

7 Physical vs Magnetic Nanostructures Track Disk Sector Key Metrology Needs: Physical Grain struture Magnetic Imaging at grain level D = 9.9 ± 2.6 nm Characterization of cluster size <D*> and it s dependence on intergranular magnetic exchange Physical Grains <D> Magnetic Clusters <D*> Dieter Weller Page 7

8 Physical Size - Segregation Mechanism CoPt 12 Cr nm CoNb 8 Zr nm a-c 5 nm CrTa 1 nm NiAl 4 nm Key Metrology Need: Determine grain boundary chemistry with nm resolution NiAl 7 nm EFTEM elemental mapping (Jim Wittig) O K Cr L23 Co L INSIC Reference Perpendicular Media Dieter Weller Page 8

9 Magnetic Imaging (MFM) Physical grain size below 10 nm Key Metrology Need: Sub 10 nm resolution practical magnetic imaging tool Conventional MFM High Resolution MFM 20nm AFM MFM 200 nm Conventional MFM cannot resolve magnetic fine structure Joachim Ahner, Magnetic imaging January 24, 2004 Seagate Confidential Page 9

10 Reduced media noise by tightening dispersions Norm. Freq Reduce grain size and tighten grain size distribution experiment 6.1 nm σ/d=0.23 Poor 7.9nm magnetics σ/d=0.19 unstable D=(6.1nm) stable 9.9nm σ/d= nm SNR(dB) Tighten magnetic dispersions modeling Grain Diameter (nm) σ HA /H A Bin Lu Key Metrology Challenge: Magnetic Dispersions Dieter Weller Page 10 H. Richter

11 Novel Head and Media Designs Shielded Pole Head Pancake Write Coils Write Pole Shield Pole Tilted Anisotropy Media Shields Media SUL Motion GMR Write Field Flux in SUL Figure Shielded Pole perpendicular writer design. Mike Mallary, Recording Head Design, chapter 11 in The Physics of Ultrahigh-Density Magnetic Recording, Plumer, M.L., Ek, J.van, Weller, D., Seagate Technology, USA (Eds.) Springer XII, 352 pp. Hardcover Dieter Weller Page 11 K. Gao and N. Bertram, IEEE Trans. Magn Switching field (Hsw/Hk) Conventional: CP Tilted: TP Tilt in magnetic anisotropy ( ) Tilted Fields and tilted anisotropy media reduce the switching coercivity and therefore further ease writability, which enables smaller stable grains!

12 Datarate Today: Dia=2.5 inch high end server disc drives 2πr = 0.2 m circumference, f=15,000 rpm = 250 rps Density=70 Gbit/in 2, B=45 nm bit-length Max. Linear velocity: v=250 rps x 0.2 m = 50 m/s = 50 nm / ns Max. Datarate: v/b = 50 nm / 45 nm / ns = 1.1 GHz (1 ns timescale) Future: At Tbpsi we need about 3-4x higher datarates ~ 3-4 GHz (sub ns timescale) at these linear velocities; Note: Disc diameters will likely shrink: Trend towards smaller disc drives r Dieter Weller Page 12

13 Contact Tester Switching Experiments gyromagnetic regime thermal regime Write Current (o-p) for Hc (ma) ps ~ 5ns Long Head Perp Head Perpendicular Media log time (s) Key metrology need: Quantification of Fields at write speeds (calibration of head field vs drive current); Pulse field measurements at 100 ps level Dieter Weller Page 13

14 Pump Key Metrology Need: Media Damping Large angle excursion more relevant (unlike FMR) Fast (<10ps) risetime field with large amplitudes needed Intrinsic v.s. extrinsic damping Pump-probe: Pump-induced change of H K as pulse field M (a.u.) M (a.u.) Continuous Co film, α ~ Time (ps) Media #1, α ~ 0.12 Media #2, α ~ Time (ps) H K (t) probe t pump-probe M HAMR Happ Ganping Ju Ganping Ju, Research Pittsburgh Seagate Confidential 14

15 Writer Developments Writer Materials Higher moment NiFe (magnetostriction) CoNiFe CoFe, CoFeX Shrinking Features Reduction of Topography Stitch poles CMP (sputter materials) Lithographic Improvements Reduction Steppers Phase shift Dieter Weller Page 15

16 FeCo sits at the top of the Slater-Pauling Curve Fe * CoFe FeMn Fe CoFe bccmn Co CoNi VFe CrFe Ni Cr CrMn (Mn) (Cr) Calculated points: bcc (Fe) (Co) (Cu) (Ni) fcc * not lowest energy state Courtesy: Bill Butler / Univ Alabama and Oak Ridge Dieter Weller Page 16

17 For > 100 Gb/in 2 : Sensor Technologies Theoretical Limits AMR (~3%) Experimental/Practical #s AMR (~2%) CIP-SV (20-30 %) Today CIP-SV (~20 %) TMR TMR (40-50%) CPP-GMR (up to 100%) Cap Free Layer Oxide Barrier Reference Layer Ru Pinned Layer AFM Seed Layer? TMR (20-30%) CPP-GMR (up to 50%) Cap Free Layer Cu Reference Layer Ru Pinned Layer AFM Seed Layer CPP-GMR Mike Seigler Dieter Weller Page 17

18 TMR Read Sensor Energy Barrier FM 1 FM 2 Distance Spin polarization P 1,2 = ρ ρ ρ 1,2 1,2 + ρ 1,2 1,2 Julliere s formula 2PP TMR 1 2 = 1 PP 1 2 Shield Shield ~12 Å Al 2 O 3 barrier Free Layer 5 nm SAF 5 nm Dieter Weller Page 18

19 Reader Materials & Processing Challenges Atomic level control of layer thicknesses and interfaces. Thicknesses of some films are <10Å, so almost all atoms are at an interface. Achieving small dimensions. 1 Tbpsi will require ~30 nm sensor widths. Edge effects. Processing techniques need to be compatible with other materials and processes uses. Highly spin polarized materials, which leads to a large GMR. Dieter Weller Page 19

20 Heat Assisted Magnetic Recording (HAMR) Laser GMR Element Heated Spot Shield Perpendicular Recording HAMR Current research indicates HAMR with thin film media could enable 10 Tbpsi. Research Overview December 18, 2003 Page 20

21 Areal Density Scaling AD ~ 1/D p 2 (arb units) Co/Pt 10 nm MnAl CoPt Fe 14 Nd 2 B FePt FePd 200 Co CoPt 3 Pt 3 10 AD gain potential Co/Pd CoCrPt with FePt K u (10 7 erg/cm 3 ) 2K ( ) u TS δ AD 1 N rk kbt 4πM ( ) S TS ( ) H K TS T S =storage temperature r K =f(σ V,σ E,T storage,t Storage ) N=number of grains per bit δ=film thickness M S =saturation T storage H K =anisotropy T storage K u =anisotropy energy T storage AD K u (T S ) 2 Scaling option: taller, smaller diameter grains! Dieter Weller Page 21

22 Heat Assisted Magnetic Recording 140 Store: 350K Write: 770K Media Design anisotropy field H K (koe) Callen&Callen Model FePt Available Head Field 770 K temperature (K) FePt L1 0 Recording at or near Curie Temperature! Issue: >400 o C interface temperatures! Growth layer = thermal isolation layer Heat sink CuZr, Au,Al Au,Al, Cu etc. Substrate Thermal management via heat sink to obtain rapid cooling after writing (<ns) Dieter Weller Page 22

23 Complete Media Stack on Cu Heat Sink mag. media 1.0 Seed/interlayer fit (λ 0 =36nm): D= m 2 /s nm Cu R (normalized) D eff =18.5e-6 m 2 /s 0.2 Glass Substrate pump-probe delay (ps) Excellent cooling speed Julius Hohlfeld, Ganping Ju et al. Dieter Weller Page 23

24 Ridge waveguide transducer Ridge waveguide transducer on a silver film is illuminated with focused light. L = 218 nm, W = 38 nm. P = 19 nm, G = 20 nm, T = 64 nm. Following result is for 100 mw input power. FWHM spot size is 31 nm. Ridge waveguide Maximum power density = 1.67*10-4 mw/nm 3 P ~ 2 mw in (25nm) 2 x15nm bit Absorbed optical power density profile Spot size = 31 nm Dieter Weller Page 24

25 Heat Assisted Magnetic Recording Summary HAMR has been shown to operate with performance comparable to magnetic recording at low densities. Problem of making a practical near-field head remains, but designs using surface plasmons show promise. Design of a reliable HDI remains a problem, but we believe it is solvable. HAMR could make it possible to use the smallest possible thermally stable grain, irrespective of the anisotropy/coercivity For 10 nm thick FePt, this is about 2.4 nm. Assuming 20 grains/cell, this corresponds to about 5 Tbit/in 2. Using the 10 grains/cell criterion and ECC that R. Wood used in his early proposal for 1 Tbit/in 2, 10 Tbit/in 2 would be achievable. Dieter Weller Page 25

26 Bit Patterned Media Lithography vs Self Organization Lithographically Defined FePt SOMA media Major obstacle is finding low cost means of making media. At 1 Tbpsi, assuming a square bit cell and equal lines and spaces, 12.5 nm lithography would be required. Semiconductor Industry Association roadmap does not provide such linewidths within the next decade. 6.3+/-0.3 nm FePt particles σ Diameter 0.05 S. Sun, Ch. Murray, D. Weller, L. Folks, A. Moser, Science 287, 1989 (2000). Dieter Weller Page 26

27 International HDD Roadmap for Alternate Technology Chairs: Gordon Hughes/CMRR and Yoshio Suzuki/Hitachi Self Organized Magnetic Arrays (SOMA) - Dieter Weller/Seagate SOMA is viewed as a strategy to achieve bit-patterned media without having to lithographically define each bit. SOMA media can serve as (i) conventional media with reduced grain size dispersions (ii) bit-patterned media with bit-transitions defined by rows of particles (iii) single-particle-per-bit recording. Under optimistic conditions areal densities of Terabit per square inch become possible (10 years, 300K). This requires a combination of SOMA and HAMR. Many Issues and Challenges to make SOMA work! Dieter Weller Page 27

28 Key Challenges to Make SOMA work = University research topics! 1. Size and Shape Control 2. Packing of spheres is dismal (<30%); need columns 3. Surface vs Bulk properties: Effect of surfactant on magnetics! High ratio of surface to volume! Need ab-initio models to understand implications such as effect on Ms, Ku etc, switching mechanism 4. FCC-FCT Transformation: Can ordering temperature be reduced? Recent literature suggests that >700 o C anneal necessary! 5. Sintering: Agglomeration Atomic Exchange Sintering Grain Growth. Better/harder coatings/core shell? Better adhesion of particles to substrate to avoid detachment and mobility during anneal! 6. Magnetic Easy Axis Control Annealing in Field doesn t work! Need new ideas? Deposition in Field? 7. Large Scale Ordering Uniformity, Surface roughness control, thickness control Dual Patterning How precisely do the particles have to align to the groove wall? 8. Tribology Dieter Weller Page 28

29 Self Organized Magnetic Array Media Potential Toward single particle 1 2 per bit recording! 130 nm 3 9 Tbpsi 1 Conventional Granular Media Thermal Stability Limt 3 nm >40 Tbit/in 2 2 Bit Patterned Media 3 Single-Grain-Per-Bit Patterned Media Development time: ~ 13 60% CAGR and ~22 30% CAGR Dieter Weller Page 29

30 Magic numbers for a perfect Truncated Octahedron atom numbers size(nm) Long Term Metrology Need: Magnetometry with single particle sensitivity ~ emu for 3 nm dia particle (111) (002) (111) (111) (220) Dieter Weller Page 30 Tim Klemmer et al.

31 130 nm HAMR + SOMA Patterned Media: Vision to reach single particle stability limit ~µm SOMA Assembly of FePt Nanopartcles on TEM Grid (0.1 µm scale) 9 Tb/in 2 6 nm FePt particles Idea: Use Pattern Assisted Assembly to Establish circumferential Tracks on Disks Max. Areal Density (Gbit/in 2 ) Single Particle Stability Limit ~40-50 Tb/in Tbit/in Gbit/in 2 LABORATORY DEMOS Products SOMA contact tester results HAMR+SOMA Availability Year FePt SOMA Media are promising candidates for 1. Perpendicular Media 2. HAMR Media 3. Probe Media (x-y storage) Dieter Weller Page 31

32 Conclusions Longitudinal recording is expected to approach limits somewhere beyond 100 Gbpsi. Perpendicular recording appears promising for extending the areal density progression -- perhaps to 1 Tbpsi. Heat assisted magnetic recording could extend the areal density to as much as 10 Tbpsi. FePt SOMA media, in combination with HAMR offer an ultimate areal density potential of 50 Tbpsi. Major Remaining Gap: Obtaining sufficiently small HMS to enable the resolutions required. Dieter Weller Page 32

33 Thanks

34 Role of large scale simulations Current computer resources are now capable of supporting highly sophisticated calculations (previous generations of supercomputer performance now exceeded by laptops) Such models can give strong support in the interpretation of experimental data and the determination of physical parameters Also, simulations can give information not easily accessible to experiment. An example follows; a computational model is fitted to the variation of coercivity with temperature. The fit gives an indication of the important materials parameters Dieter Weller Page 34 Roy Chantrell

35 Variation of Hc with T for FePt particles Hc(kOe) Parameters K=4.2e7 Dm=3.2nm σ= T (K) K(T) from Callen-Callen theory for S=3/2. Interparticle interactions are taken into account, as are dispersions in all the physical parameters. The theoretical model also provides the basis for the discrimination between exchange coupled and exchange decoupled systems based on fits to bulk magnetic measurements Dieter Weller Page 35 Roy Chantrell

36 The future Capability of computational modeling is increasing very rapidly. New generations of code will be able to predict materials properties using atomic length scale basis (multi-lengthscale approaches) The prospects associated with such code for the support of experimental metrology should not be underestimated Dieter Weller Page 36 Roy Chantrell

37 Selected metrology problems in magnetic data storage Field measurement (amplitudes and dynamics) of perpendicular head in the presence of SUL SUL is in the way for measurements, and field w/ and w/o SUL is totally different Time-resolved microscopy of individual magnetic grain switching: Kerr microscopy limited by diffraction (<1ps, 200nm) Pulsed PEEM need synchrotron source (~70ps, 100nm) Measurement of Media large angle excursion FMR: small angle Need <10ps field with >1-2 Tesla HAMR: Torque magnetometer at high temperature and high Field Ganping Ju Ganping Ju, Research Pittsburgh Seagate Confidential 37

38 HAMR Metrology Needs 1) Near Field Optical Measurements State-of-the-art is a resolution of ~ 50 nm. Advances in areas of heat assisted magnetic recording, optical storage, and lithography need resolution of ~ 5 nm. New techniques are needed that are less intrusive or the disturbance to the system is well understood. Current techniques often disturb the system under test and lead to the wrong interpretation of the results. Polarization is also a problem with current techniques. 2) Nano-scale temperature measurements Scanning probe techniques (IBM) have shown resolution of ~ 10 nm. This technique is limited in accessible geometries. Near-field Raman techniques need to be further developed to provide a less intrusive measurement with a wide temperature range ( K). 3) Modeling Optical thermal effects in sub wavelength structures are not well understood. Examples include thermal conductivity with evanescent radiation coupling and black body radiation with sub wavelength features. New models are required to extend our understanding of thermal effects into the sub-wavelength regime. 4) Optical properties of nanoscale materials (thin films, sub wavelength particles, nanoscale composites). This area seems to be well covered in the list you distributed. HAMR Team Dieter Weller Page 38

39 Method Magnetic Imaging Methods Contrast Origin Quantit ative Best Resolution (nm) Typical Resolution (nm) Acquisitio n Time Costs Vacuum Requireme nt MFM grad Bext. yes 10 nm 30 nm 5-30 min $300,000 High vacuum Spin stand imaging B 30 nm 100 nm Very fast low no Bitter grad Bext. no ~10 nm ~30 nm 1 min inexpensive SEM Spinpolarized STM M yes 0.6 > 1nm Very low, tip prep. Very high (Xray source) UHV Lorentz TEM B yes < 1nm 100nm Very slow, Sample prep TEM > $1M TEM PEEM M yes ~10 nm 50 nm Slow, sample mounting Very high (Xray source) UHV SEMPA M yes 10 nm 50 nm Dieter Weller Page 39 Slow, sample prep Very high ~$5M UHV Joachim Ahner

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