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					 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
                                                 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)
Magnetic recording areal density growth along with transistor count per
integrated circuit device (McDaniel J. Phys: Condens. Matt. 17(2005)R315).
Areal density trends in HDD magnetic recording (Fujitsu
Sci. Tech. J., 42(2006)122).
Industry first 120 GB 2.5-in Seagate Momentus Ⅱ high capacity
mobile drive using TMR reading element (IEEE on Mag. 42(2006)97).
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.
Schematic representation of longitudinal, digital magnetic
recording write process.
Transition width α (depends on Mrt / Hc)
(a) 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.
  SNR≈0.31PW50BWread / α2d(1+σ2)

         ≈B2Wread / α2 d3 (1+ζ2)


B is bit length, Wread is read width of head, α is transition
parameter, d grain diameter, ζ normalized grain size
distribution width
        Recording Media Requirements

(1) 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.
PtCoCrB films
Write head : having a sufficient high Ms so that the fringe field
             exceeds the Hc of the medium (500-3000Oe); an
             adequate magnetic permeability (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
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
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
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
Spin-Valve Read head




         h=2-6 µ m and w=10 µ m
                    Summary

(1) SNR≈0.31PW50BWread /α2d(1+ζ2)

        ≈B2 Wread / α2 d3 (1+ζ2),

(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.
           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-2 longitudinal recording
          Thermal Stability

In the physics of magnetic recording there are two key
factors in achieving very high areal density:

(1)The superparamagnetic effect (thermal stability);

(2)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.
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
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.
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
Oscillation Exchange Coupling




                                    in Co/Ru/Co MLs
              (Parkin PRL 64 (1990)2304).
     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 .
 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.
APL 77(2000)3806




                                      Fitted by Eq.(1)




(b) thermal decay at -500 reversal field.
Comparison of amplitude loss as aresult of thermal degration of
single layer media and AFC media
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.)
             Magnetic Recording

(1) 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.
perpendicular recording




    Schematic drawing of a perpendicular recording system
    with SUL and a single pole head.
   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
             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)
Perpendicular recording hard disc drive
PR recording using AF coupling media
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
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
          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
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.
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
hybrid recording




        (Solid immersion lens)

        ZnS:SiO2 NA ~1.1


      Media: Co69.48-xTb30.52Agx, x=0-25.68
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.
       Magneto-optical Effect




θ k is defined as the main polarization plans is tilted over
 a small angle;
εk = arctan(b/a).
(a) Assembly of apparatus




 (b) Rotation of polarization
 of reflecting light.
Magneto-optical Recording




  Principle of thermomagnetic recording (Curie point
writing): (a) before, (b) during and (c) after the writing.
 From Oppeneer Magneto-optical Kerr spectra in Handerbook of magnetic
 Materials, Edited by Buschow (Vol.13)




Experimental pola Kerr ritation an undoped MnBi sample (Di et al. 1992)
and Al-doped MnBi (Shang et al., 1997) sample at room temperature.
     High-density MRAM
     (Magnetic random access memories)




Schematically representation of MRAM structure and
M-H, ΔR/R characteristics of the PSV.
Schematic of the read and write processes in a PSV random access
memory.
Table: composition and dimensions of the principle layers in a current
representative MARM device.
Advantage of MRAM

(1) It combines the speed of SRAM with the non-volatility
    of flash
(2) It also offers a low-power memory solution which
    eventually may match DRAM’s capacity and density
(3) No limit for write-read cycles (flash 100,000)
(4) Radiation-resistant

7/2 2006 Toshiba and NEC, 16 megabit density, read write
speed 200 Mbytes/sec, operation at 1.8V, a chip 78.7 mm2;
9/6 basic technology for 256 Mbit

 4Mbits MRAM enter in market (2007 March meeting). As
embedded memory in Automobiles, $20 for a half megabyte.

Disadvantage
The MgO-based magnetic tunnel junction film
Ta/CuN/Ta/PtMn/CoFe/Ru/CoFeB/MgO/
CoFeB/Ta. (Lee etal., IEEE Trans on Mag 43(2007)917).




    Fig. 1.R–H loop in MgO-based MTJ.              Fig. 2. Magnetoresistance versus variatio
                                                   current in MgO-based MTJ structures
                                                   using a current pulse width of 200 s.




                                        Fig. 3. Read/write cycle test. Inset: Resistance
                                        change over 110 cycles with a current pulse
                                        width of 200 s.


                                                    STT RAM
                                     Single-crystal multilayer

                            25nm(Ga0.95Mn0.05)As/500nm(In0.15Ga0.85)As/
                            100nmGaAs on (001) semi-insulating GaAs
                            Substrate (Tc=90K).



                            (a) a 20 µm wide channel with three pairs of Hall
                            probes.

                            (b) a domain wall was prepared at the boundary
                            of regions 1 and 2, and its position after application
                            of a current pulse was monitored by RHall=VHall/l,
                            Hc1 >Hc3 >Hc2




Yamanouchi et al Natural 428(2004)539
minus Plus pulse   83K




                           At t=0, the domain wall is at the boundary
                         of regions 1 and 2; when a negative current
                         pulse is applied, M direction in region 2 is
                         reversed.
      initial state   After I=-300 µA   After I=+ 300 µA



MOKE images of sample A using 546 nm light at 80K.
The future of scalable STT-RAM as a universal embedded memory
By Farhad Tabrizi, Grandis, Inc. (02/21/2007)




      Fig. 1. STT-RAM addresses each bit individually by flowing
      current directly through the bit. Unintended writing errors
      are completely eliminated.
Fig. 1. STT-RAM addresses each bit individually by flowing current
directly through the bit. Unintended writing errors are completely
eliminated.
Fig. 2a " Conventional MRAM cell. A magnetic field, generated
by the bit line, cladding, and write word line, is used to switch
between the "0" and "1" states.
Fig. 2b " STT-RAM cell. By eliminating the write word line,
bypass line and cladding, a STT-RAM cell is considerably
smaller than a conventional MRAM cell.
Fig. 2c " Total required current in STT-RAM continues to
scale lower with increasingly smaller geometries. Conversely,
conventional MRAM switching current increases with smaller
geometries.
                                          spin polarization along the axis
                                         parallel to the vector ML of local
                                         ferromagnetic polarization in will
                                         be present in the electrons
                                         impinging on MR.


                                            S1,2 = (Ieg/c)S1,2 x (S1 x S2)

                                            g = [ -4+(1+p)3(3+S1·S2)/4p3/2]


                                         (J.C.Slonczwski 3M 159(1996)L1)



(C.Heide et al., PRB 63(2001) 064424).
NANORING for MRAM




 Fig. 1. Plan-view and side-view scanning micrographs of a and b arrays
 of Co circular rings, c NiFe/FeMn elliptical rings, d NiFe/Cu/Co elliptical
 rings, and e and f NiFe/Cu/Co pseudo-spin-valve elliptical ring
 device with six nonmagnetic contact wires.
Nanoring for MRAM




We have achieved nearly 100% vortex reversal in the asymmetric
nanorings, while the symmetric nanorings can accommodate only 40%.
PRL 96(2006)027205
Nanoring fabrication




   (a) AAO (porous anodic aluminium oxide membranes), (b) 100 nm Fe film
   by RF, (c) and (e) Fe nanoring in AAO pores.
SEM micrograph of the top view of the as –prepared AAO template.
The inset shows the oblique view of AAO showing the aligned nano-
channls.
  Samsung offers flash disk as laptop upgrade

  Report by Robinson in COMPuting, 22 May 2007
-------------------------------------------------------------------------------------------------------------

 From the end of Jun, the 32GB SSD will be sold through
memory specialist just Rarm as part of its integral brand
For $350 ,


64GB model is due ship in the coming months
 Competition Between Hard Disc and Flash Disc
-------------------------------------------------------------


     Flash can be a potential replacement for hard disks
  because of its high performance, noise free running, light
  weight, fast data access and less power consumption.


   iSuppli believes that by the fourth quarter of 2009, 24 million
 Notebooks will be sold with some form of flash data storage,
 compared to 143,600 in the first quarter of 2007.
   That's nearly 60 per cent of anticipated laptop sales.

    But the price factor is still the most active barrier.
                 Magnetic Hard Disc

Freecom Mobile HDD Drive 160GB USB-2, Release Date: Wednesday
2nd May 2007,Our Price: £78.95 ; LaCie 500GB USB 2.0 Hard Drive,
Release Date: Wednesday 20th September 2006, Our Price: £114.95

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)
       Lui et al., APL 76(2000)2749
RRAM
 材料电阻会因施加的电压脉冲而发生巨变(大约在1万~10万
倍之间)的现象。停止施加电压脉冲后,可维持变化后的电阻值。
利用这种现象而形成的非挥发性内存就是RRAM。
 十仓领导的研究小组认为,这种大范围的电阻变化可能缘于一种
名为“强相关(strongly correlated)”的现象。强相关是指,
某种材料不经过半导体而在绝缘体与金属之间进行迁移。激发这种
现象的就是电压脉冲。



 due to de-localization of localized valence electrons
by high electric fields (IEEE 2005).
    Sharp Develops Basic Technology for RRAM,
        Next-Generation Nonvolatile Memory
--------------------------------------------------------------------------
                                                              Dec 11 ,2006


  A memory capable of programming data at rates about 100 times
faster than flash memory.

   These results are the first step toward the practical use of this memory
technology. It will continue in the future aimed at bringing a commercially
viable product to market.
    Philips claims 'super Flash' memory breakthrough
      May/2005


 the 'phase-change' material changes phase from one to another using
pulses of electric current.

 A doped Antimony Tellurium (SbTe) compound, unlike other attempts at
phase-change memory, well-suited to the standard CMOS process used to
make most computer chips.

  The material's phase change is fast, taking place in under 30ns, in the
prototype cell. That is 100 to 200 times faster than today's Flash memory
cells, and getting awfully close to DRAM speeds.
         Phase change vs Magneto-optics

Phase change              2001              next generation, 2003-2004

Products                 DVD-RAM            UDO(1)    nextGen DVD(2)
Capacity/surface, GB    4.7                   20               25
No of surface           2                     2                2/4
Bit area mm x mm        0.165x0.28          0.33x0.13     0.32x0.185
Transfer rate Mb/s      1.2                   4-8              4-6

Magneto-optics

Products                 3.5 in GIGMO(3)    ID photo(4) 3.5 in GIG     ID Photo
Capacity                 2.3                   0.73       10.0            3.0
No of surface             1                    1           1               1
Bit area                  0.67x0.233         0.6x0.235
Transfer rate             8.38               2.5         20+              110

 (1) SONY disc diameter=13 cm, (2) Matsushta prototype, two recording layers
 (3) disc diameter=9cm, (4) disc diameter=5 cm.
 Sony: 23GB, 11Mb/s (2003); 50GB, 22Mb/s (2005);100GB,43 MB/s (2007)
   HARM+PM

HARM
                   holographic technology

  Two coherent beams are necessary.The one is an information b
including user data, the other is a reference beam. During the reco
process, they interfere with each other, and the interference patter
recorded in the media, called a hologram.

   In the reconstructing process, the information beam can be reco
structed when the reference beam incident on the hologram.
                      SUMMARY
(1) Longitudinal Recording
   AD 120Gbits/in2
   SNR ≈ B2 Wread / α2 d3 (1+ζ2),
   Thermal stability KuV/KBT ≌ 50 – 70

(2) Perpendicular Recording
   AD 421 Gbits/in2

(3) Advantage > 1Tbits/in2
   Patterned media
   Heat assisted magnetic recording
   STT RAM (Nano-ring)                   FRAM
   RRAM                                  PRAM
   Super Flash (PRAM)                    FLASH (32Gbits)
References
(1) Magnetic Recording :Advancing into the future
   A.Moser, K.Takano et al.,
    J. Phys.D:Appl.Phys. 35(2002)R157-167.
(2) Longitudinal Magnetic Media Designs for 60-200Gb/in-2 Recording
   Gerardo A. Bertero et al.,
    IEEE Trans. on Mag. 39(2003)651.
(3) The limits to magnetic recording ---media consideration.
    K.O’Grady, H.Laidler
    J of Magn. Magn. Matt. 200(1999)616-633.
(4) Recording on bit-patterned media at densities of 1Tb/in2 and beyond
    H.J.Richter et al., IEEE Trans on Mag 42(2006)2255.
(5) Heat-assisted magnetic recording
    R.E.Rottmayer et al., IEEE Trans on Mag 42(2006)2417.
(6) Magnetic bistability and controllable reversal of asymmetric ferromag-
    netic nanorings
    F.Q.Zhu et al., PRL 96(2006)027205.
(7) Current-driven switching of magnetic layers
    C.Heide et al., PRB 63(2001)064424
Thanks !
Takuo Tanaka and Satoshi Kawata
Three-Dimensional Multilayered Optical Memory Using
Two-Photon Induced Reduction of Au3+ Doped in PMMA

Akihiro Ohta, Masao Miyamoto, Yoshimasa Kawata, and Masahito
Nakabayashi
Multilayered Optical Memory for Terabyte Data Storage

(IEEE TRANSACTIONS ON MAGNETICS, VOL. 43, NO. 2, FEBRUARY 2007)
          Ferroelectric Memories, March 2007

   The traditional FeRAMs continue to be used in applications such as
smart cards and ID cards as well as targeting RFID, automotive and
space. Other ferroelectric memory devices such as organic polymer
ferroelectric FeFET memories are exciting new interest as well.

   At least 10 companies continue to work on ferroelectric memories
 for various applications such as fast, low power memory technology
for embedding in SoC. Several novel ferroelectric memory applications
 have been discussed such as high density probe memory and
 associative memory. Multi-bit FeRAMs have been shown which could
 help with density and scaling issues.

				
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