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

Areal density progress in magnetic recording since its invention(Moser et al. J.Phys D: Phys. 35(2002)R157-167)

1Tbits/in2

100Gbit in-2

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

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

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

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

Schematic representation of longitudinal, digital magneticrecording 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+σ 2)

≈B2Wread / α2 d3 (1+σ2)

B is bit length, Wread is read width of head, α is transitionparameter, d grain diameter, σ normalized grain size distribution width

(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 Ms

2/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.

Recording Media Requirements

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 mediumand head material.

For write head: µ >>1, Ms large and Br=0;For read head: µ >>1 , Hc = 0

Thin film recording head. Left, layout of pole pieces and windings; right, enlarged, cross-sectional view of magnetic pole pieces

Film thickness2-3 micrometer;Gap 200 nm.

Thin film recording head

h=1-2 µm, w=2-4 µmt=10-20 nmΔρ/ρ =2.0% Ni81Fe19

Magnetoresistive read head (1980-90 from 10 -100 Mbit in-2)

Spin-Valve Read head

h=2-6 µ m and w=10 µ m

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.

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

The develop of the magnetic recording

Thermal Stability

In the physics of magnetic recording there are two keyfactors 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 withthe ambient thermal energy.

The signal to media noise is approximately by the numberof 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≌

A favorable lattice matchingbetween CoPtCrB (1120)[0001]Is parallel to CrX (002)[110].Toney et al., IEEE Trans. On Mag99(2006)033907.

Oriented longitudinal media (Ku)

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 substrateanisotropic etching of the substratedirectional deposition of the media

(Parkin PRL 64 (1990)2304).

Oscillation Exchange Coupling

in Co/Ru/Co MLs

Interlayer antiferromagnetic coupling media

Schematic illustration of (a) a two layered AFC media,(b) LAC media with high J and (c) advanced three layersLAC media for much lower Mr δ .

Longitudinal

Mr t = Mr t1 – Mr t2

KuV1<KuVeff < (Ku V1+KuV2)

KuV/KBT 50 - 70≌

In the case of two layers AFC media

single layer media (a) and (b) anAFC media, Jex=0.06 erg/cm2,Hex~800 Oe.

(b) thermal decay at -500 reversal field.

Fitted by Eq.(1)

APL 77(2000)3806

Comparison of amplitude loss as aresult of thermal degration ofsingle 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 27Track width, W (nm) 280 115Magnetic coecivity, Hc (Oe) 4000 5000Mrt (memu/cm2) 0.32 0.2Grain size (nm) 8.1 6Head to media spacing (nm) 30 15Shield to shield spacing, g(nm) 700 500

Transition parameter, a (nm) 12.8 6.2Pulse width PW50 (nm) 99 54User 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.

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

perpendicular recording

Advantages of PA recording:

a. high orientation ratiob. lower media noise (α smaller)c. increase of signal and thermal stabilityd. writing field large

*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 quarterof 2007),

*In the first half of 2007, Hitachi has brought hard drive arealdensity 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

Perpendicular recording hard disc drive

PR recording using AF coupling media

Magnetic recording on a CoPd/Pd/CoPd dot array: (a) GMR readback signalsafter 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

1Tbit in-2 for 40nm period

(a) topography image of the patterned area. P2 is write pole. (b) Magneticforce microscopy image of a square wave pattern

Patterned media made by a focused ion beam

Thermal stable, even if Ku is small; transition parameter

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

1 Tbit/in2 for patterned media

TEM image of a 3D assembly of FePt nanoparticles. Image size is 130nm x130nm and particle diameter is 4nm.Nanopartical media are made in a chemical process, then annealed to obtaina hard magnetic phase.

Nanoparticle media (self arrangements)

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

HAMR

McDaniel SeagateUltimate limit to thermally assisted magnetic recordingJ 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

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 Libraryof Congress ( ~10Tb) could be stored on a 30 mm diameter disk (50Tb/in2). This is about the size of US fifty-cent coin.

Fujitsu paves way for 5TB hard drives (1Tbits/in2, 04/12/2006 demo a spot size 88nm x60nm using HSRM)

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 pointwriting): (a) before, (b) during and (c) after the writing.

From Oppeneer Magneto-optical Kerr spectra in Handerbook of magneticMaterials, 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 andM-H, ΔR/R characteristics of the PSV.

Schematic of the read and write processes in a PSV random accessmemory.

Table: composition and dimensions of the principle layers in a currentrepresentative 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

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

Fig. 3. Read/write cycle test. Inset: Resistancechange over 110 cycles with a current pulsewidth of 200 s.

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).

STT RAM

(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

Single-crystal multilayer

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

At t=0, the domain wall is at the boundaryof regions 1 and 2; when a negative currentpulse is applied, M direction in region 2 is reversed.

minus Plus pulse 83K

initial state After I=-300 µA After I=+ 300 µA

MOKE images of sample A using 546 nm light at 80K.

Fig. 1. STT-RAM addresses each bit individually by flowing current directly through the bit. Unintended writing errors are completely eliminated.

The future of scalable STT-RAM as a universal embedded memoryBy 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. 2a " Conventional MRAM cell. A magnetic field, generatedby 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).

Fig. 1. Plan-view and side-view scanning micrographs of a and b arraysof Co circular rings, c NiFe/FeMn elliptical rings, d NiFe/Cu/Co ellipticalrings, and e and f NiFe/Cu/Co pseudo-spin-valve elliptical ringdevice with six nonmagnetic contact wires.

NANORING for MRAM

Nanoring for MRAM

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

(a) AAO (porous anodic aluminium oxide membranes), (b) 100 nm Fe filmby RF, (c) and (e) Fe nanoring in AAO pores.

Nanoring fabrication

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 brandFor $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 inchdesktop (41650 hours music, 800,000 photo, 4100 hoursdigital 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 commerciallyviable 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 tomake most computer chips.

The material's phase change is fast, taking place in under 30ns, in theprototype 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 25No of surface 2 2 2/4Bit area mm x mm 0.165x0.28 0.33x0.13 0.32x0.185Transfer 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 PhotoCapacity 2.3 0.73 10.0 3.0No of surface 1 1 1 1Bit area 0.67x0.233 0.6x0.235Transfer 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

HARM+PM

holographic technology

Two coherent beams are necessary.The one is an information beamincluding user data, the other is a reference beam. During the recordingprocess, they interfere with each other, and the interference pattern isrecorded in the media, called a hologram.

In the reconstructing process, the information beam can be recon-structed when the reference beam incident on the hologram.

SUMMARY(1) Longitudinal Recording AD 120Gbits/in2 SNR ≈ B2 Wread / α2 d3 (1+σ2), 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) RRAM Super Flash (PRAM)

FRAMPRAMFLASH (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 KawataThree-Dimensional Multilayered Optical Memory Using Two-Photon Induced Reduction of Au3+ Doped in PMMA

Akihiro Ohta, Masao Miyamoto, Yoshimasa Kawata, and Masahito NakabayashiMultilayered 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.