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Magnetic Data Storage

Magnetic Data Storage. (1) Magnetic recording (a) General (longitudinal recording) (b) Thermal stability (c) Advantage Media Oriented longitudinal media Anti-ferromagnetic coupling media Perpendicular recording Pattern media and nano-particle media

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Magnetic Data Storage

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  1. Magnetic Data Storage (1) Magnetic recording (a) General (longitudinal recording) (b) Thermal stability (c) Advantage Media Oriented longitudinal media Anti-ferromagnetic coupling media Perpendicular recording Pattern media and nano-particle media High Ku medium (HAMR) (2) Magneto-optical recording (3) MRAM (STT RAM) and Flash disc (4) RRAM and PRAM (Random Access Memory) (5) Optical storage and other memory

  2. 1Tbits/in2 100Gbit in-2 Areal density progress in magnetic recording since its invention (Moser et al. J.Phys D: Phys. 35(2002)R157-167)

  3. Magnetic recording areal density growth along with transistor count per integrated circuit device(McDaniel J. Phys: Condens. Matt. 17(2005)R315).

  4. Areal density trends in HDD magnetic recording (Fujitsu Sci. Tech. J., 42(2006)122).

  5. Industry first 120 GB 2.5-in Seagate Momentus Ⅱ high capacity mobile drive using TMR reading element(IEEE on Mag. 42(2006)97).

  6. Schematic drawing of longitudinal recording system. B is the bit length, W is the track width and t is the medium thickness. d is flying height of the head abov the medium.

  7. Schematic representation of longitudinal, digital magnetic recording write process.

  8. Transition width α(depends on Mrt / Hc)

  9. magnetization of two transition at x=0 and 200nm. • (b) magnetic field detected by read head, solid line is for longitudinal. • pw50 is shown for a read head with zero gap.

  10. SNR≈0.31PW50BWread / α2d(1+σ2) ≈B2Wread / α2 d3 (1+σ2) B is bit length, Wread is read width of head, α is transition parameter, d grain diameter, σ normalized grain size distribution width

  11. Recording MediaRequirements • for few particles per bit, the transition becomes less • sharp and pickup signal decreases. About 400 isolated • particles are required. (2) Noise is due primarily to the formation of zigzag transition between bits and this sawtooth pattern scales roughly as Ms2/Ku1/2, (3) the signal is proportional to the number of measured events or particles per bit, N. Hence SNR ~ N1/2. (4) the heads must approach to the hard disc surface.

  12. PtCoCrB films

  13. Write head : having a sufficient high Ms so that the fringe field exceeds the Hc of the medium (500-3000Oe); an adequate magneticpermeability (easy saturated). Read head:low Hc, low noise and extremely high permeability in order to respond with a substantial change in flux to the weak fringe field above the medium

  14. Schematic M-H loop for ideal magnetic recording medium and head material. For write head: µ >>1, Ms large and Br=0; For read head: µ >>1 , Hc = 0

  15. Thin film recording head Film thickness 2-3 micrometer; Gap 200 nm. Thin film recording head. Left, layout of pole pieces and windings; right, enlarged, cross-sectional view of magnetic pole pieces

  16. Magnetoresistive read head (1980-90 from 10 -100 Mbit in-2) h=1-2 µm, w=2-4 µm t=10-20 nm Δρ/ρ =2.0% Ni81Fe19

  17. Spin-Valve Read head h=2-6 µ m and w=10 µ m

  18. Summary (1) SNR≈0.31PW50BWread /α2d(1+σ2) ≈B2 Wread / α2 d3 (1+σ2), (2) Transition width α(depends on Mrt / Hc) (3) Signal: small Mrt, large Hc, small distance between head and disc, large GMR or TMR (4) Areal density: decreasing the dimensions: B, WRead, diameter of grain.

  19. The develop of the magnetic recording Before 1985:γFe2O3 medium, Ferrite ring head (～10Mbin-2) 1980: 1st thin film read head, continuous magnetic thin film with high Hc, small α(25% CGR); 1990: 1st MR read head, decreasing thickness and, in turn, the transition distance (80% CGR); 1997: 1st GMR read head (100% CGR); 2000: 1st AFM medium, increasing the effective volume. 2006: 1st TMR head for 80-100 Gbit in-2longitudinal recording

  20. Thermal Stability • In the physics of magnetic recording there are two key • factors in achieving very high areal density: • The superparamagnetic effect (thermal stability); • The finite sensitivity of the readback head. • In both cases, the limitations arise because the signal • energy becomes so small as to be comparable with • the ambient thermal energy.

  21. The signal to media noise is approximately by the number of magnetic grains (or switching units) per bit: SNRmedia~ Wbt / V Where, wbt (bit volume, read-width x bit-length x thickness) v (the grain volume) In order to avoid thermal instability, a minimal stability ratio of stored magnetic energy, KuV, to the thermal energy, KBT, KuV/KBT ≌ 50 - 70

  22. Oriented longitudinal media (Ku) A favorable lattice matching between CoPtCrB (1120)[0001] Is parallel to CrX (002)[110]. Toney et al., IEEE Trans. On Mag 99(2006)033907.

  23. A perfect orientation (large Ku) carries out: (1) a low media noise (2) a high signal level (3) a smaller transition parameter (4) a narrower switching field distribution OR = Mr / Mr per >2.5 for current L media mechanically texturing metal disk substrate anisotropic etching of the substrate directional deposition of the media

  24. Oscillation Exchange Coupling in Co/Ru/Co MLs (Parkin PRL 64 (1990)2304).

  25. Interlayer antiferromagnetic coupling media Longitudinal Schematic illustration of (a) a two layered AFC media, (b) LAC media with high J and (c) advanced three layers LAC media for much lower Mr δ .

  26. In the case of two layers AFC media Mr t = Mr t1 – Mr t2 KuV1<KuVeff < (Ku V1+KuV2) KuV/KBT ≌ 50 - 70 single layer media (a) and (b) an AFC media, Jex=0.06 erg/cm2, Hex~800 Oe.

  27. APL 77(2000)3806 Fitted by Eq.(1) (b) thermal decay at -500 reversal field.

  28. Comparison of amplitude loss as aresult of thermal degration of single layer media and AFC media

  29. System parameters for estimating transition width and PW50 Design (AFC media) 60Gb in-2 200 Gb in -2 Bit length, B (nm) 38 27 Track width, W (nm) 280 115 Magnetic coecivity, Hc (Oe) 4000 5000 Mrt (memu/cm2) 0.32 0.2 Grain size (nm) 8.1 6 Head to media spacing (nm) 30 15 Shield to shield spacing, g(nm) 700 500 Transition parameter, a (nm) 12.8 6.2 Pulse width PW50 (nm) 99 54 User bit density (pw50/B) 2.6 2.11 IEEE on Mag. 39(2003)651 (Komag Inc.)

  30. Magnetic Recording • Traditional longitudinal recording is approaching to • its limit (100 Gbit in-2 is achieved ). • (2) perpendicular recording offers about 421Gbit/in2 • (Seagate demo) and 178.8Gbit/in2 (market). • (3) the next big challenge is 1 Tbit in-2 for recording • industry. • The possible models : pattern media; high Ku media • (HAMR); STT (Spin torque transfer) – RAM.

  31. perpendicular recording Schematic drawing of a perpendicular recording system with SUL and a single pole head.

  32. Advantages of PA recording: a. high orientation ratio b. lower media noise (α smaller) c. increase of signal and thermal stability d. writing field large

  33. Perpendicular Recording *Toshiba extends 2.5-inch mobile HDD Family with 200GB market-leading capacity (178.8 Gb/in2) (May 2007 market), *Fujitsu intros 250GB perpendicular drive (second quarter of 2007), *In the first half of 2007, Hitachi has brought hard drive areal density halfway to the 345 Gbits/sq. in. market with the 1 TB, 3.5-inch (Deskstar 7K1000). * Seagate 500GB for 2.5-inch (notebook), 2.5TB for 3.5 inch desktop (41650 hours music, 800,000 photo, 4100 hours digital video) to emerge in 2009. (Hitachi demo)

  34. Perpendicular recording hard disc drive

  35. PR recording using AF coupling media

  36. 1Tbit in-2 for 40nm period Magnetic recording on a CoPd/Pd/CoPd dot array: (a) GMR readback signals after dc magnetizing the sample (00) state and after applying a write pulse of 30 and 50 mA, creating, respectively, states (01) and (11);(b) SMRM image

  37. Patterned media made by a focused ion beam (a) topography image of the patterned area. P2 is write pole. (b) Magnetic force microscopy image of a square wave pattern Thermal stable, even if Ku is small; transition parameter

  38. 1 Tbit/in2 for patterned media The islands are lithographically patterned into regular array in the recording medium; For 1 Tbit in-2, the island array periodicity is 25 nm and the lithographic linewidth is ~12.5 nm for equal island and trench width. The transitions must be precisely written between two islands

  39. Nanoparticle media (self arrangements) TEM image of a 3D assembly of FePt nanoparticles. Image size is 130nm x 130nm and particle diameter is 4nm. Nanopartical media are made in a chemical process, then annealed to obtain a hard magnetic phase.

  40. HAMR AD = pδK / hNkBT δ= 10nm, K=7x107 erg cm-3 h= KV/kBT= 60, T=330K, p=0.56 Lbit =2.64 nm(10-12 atoms) cross-section of the bit, 60-80 atoms volume 8 x 8x 50=3200 to 9 x 9x 50=4050 atoms Given AD≈92 Tbin-2 McDaniel Seagate Ultimate limit to thermally assisted magnetic recording J Phys:C 17(2005)R315-332

  41. hybrid recording (Solid immersion lens) ZnS:SiO2 NA ~1.1 Media: Co69.48-xTb30.52Agx, x=0-25.68

  42. Fujitsu paves way for 5TB hard drives (1Tbits/in2, 04/12/2006 demo a spot size 88nm x60nm using HSRM) SmCo has a Ku value about three times high FePtX, and this might push AD estimate into 250-300 Tbin-2. The entire printed contents of the United State Library of Congress ( ~10Tb) could be stored on a 30 mm diameter disk (50Tb/in2). This is about the size of US fifty-cent coin.

  43. Magneto-optical Effect θ k is defined as the main polarization plans is tilted over a small angle; εk= arctan(b/a).

  44. (a)Assembly of apparatus (b) Rotation of polarization of reflecting light.

  45. Magneto-optical Recording Principle of thermomagnetic recording (Curie point writing): (a) before, (b) during and (c) after the writing.

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