Nanoelectronics

Semestr letni 2009

Tomasz Stobiecki

AGH Katedra Elektroniki

Magnetoelectronics

HDD for 50 years and now

First Hard Disk Drive with 24" Diameter Disks Compared with Modern 2.5" HDD. The first HDD was

introduced in 1956 with 50 disks of 24" diameter holding a total of 4.4 Mbytes of data. The purchase price of

this HDD was $10,000,000 per Gbyte. For comparison in the foreground a modern HDD is shown holding 160

Gbyte of data on two 2.5" diameter disks at a purchase price of less than $1 per Gbyte.

Miniaturyzacja

Areal data storage density vs. time for inductive and MR read heads

Disc driveThe slider carrying the magneticwrite/read head. The slider ismounted on the end of headgimbal assembly (HGA)

The air-bearing surface (ABS) allowing the head to fly at a distanceabove the medium about 10 nm

The magnetic disks (up to 10) indiameter 1 – 5.25 inches. 5.400 –15.000 RPM it is related to about100 km/h

Schematic representation of a longitudinal recordingprocess

Magnetic force micrograph (MFM)ofrecorded bit patterns. Track width is350 nm recorded inantiferromagnetic coupled layers(AFC media)

1986 – oscillatory interlayer exchange coupling (IEC) in Fe/Cr/Fe multilayersP. Grünberg et al. Phys. Rev.Lett. 57 (1986), 2442

1988 – Giant Magnetoresistance (GMR) in Fe/Cr/Fe multilayersM. N. Baibich,..., A.Fert,.. et.al. Phys. Rev.Lett. 61 (1988), 2472

1991 – Spin Valve (SV) in NiFe/Cu/NiFe/FeMnB. Dieny, et al. Phys. Rev.B (1991)

1995 – Tunnel Magnetoresistance (TMR =15%) in CoFe/Al2O3/CoJ.S. Moodera, et al. Phys.Rev.Lett, 74 (1995)

2004 – Giant TMR at room temperature with MgO(100) barrier; TMR=220% CoFe/MgO/CoFeS.S.P. Parkin et al.- Nature vol.3 December (2004), 86

2006 – Hayakawa et al.- APL 89 (2006),23 2510; TMR =472%CoFeB/MgO/CoFeB

Historia spintroniki

Structure of Fe film/ Cr wedge/ Fe whisker illustrating the Cr thickness depen-dence of Fe-Fe exchange. Above, SEMPA image of domain pattern genera-ted from top Fe film. (J. Unguris et al., PRL 67(1991)140.)

Interlayer Exchange Coupling (IEC)

Thickness dependnce of Cu spacer

GMR ⇒ due scattering into the empty quantum states above the Fermi level ⇒ ρ ∝D(EF)

For ferromagnetic 3d metals D↑(EF) ≠ D↓(EF) ⇒ρ↑ ≠ ρ↓

Spinowo zależne przewodnictwo elektryczneSpinowo zależne przewodnictwo elektryczne

M

Analogia do równoległego połączenia dwóch rezystancji

R duże

I

M

R małe

I

Spin Polarization, Density of States (DOS)

Ferromagnetic metal (Fe)

↓↑

↓↑

+

−=

nnnn

P

Spin Polarization

Ni 33 %

Co 42 %

Fe 45 %

Ni80 Fe20 48 %

Co84 Fe16 55 %

CoFeB 60%

Material Polarizations

Normal metal (Cu)

EF

Majority Spin Minority Spin

E

DOS

nn

↓↑

↓↑

>>

ρρ)()( FF EnEn

↓↑

↓↑

==

ρρ)()( FF EnEn

N

EF

Majority Spin Minority Spin

E

DOS

nn

Density of states 3d

GMR ⇒ due scattering into the empty quantum statesabove the Fermi level ⇒ ρ ∝D(EF)

Zasada działania zaworu spinowego Zasada działania zaworu spinowego ((SpinSpin--ValveValve) w głowicy twardego dysku) w głowicy twardego dysku

AFM I = const

USignal

AFM: FeMn, NiO, NiMn, IrMn

FM: Co, Fe, NiFe, CoFe

NM: Cu, Ag, Au

1 0 10 1 0

kierunek ruchu nośnika informacji

Warstwa mocująca(pin-layer)

warstwa zamocowanawarstwa swobodna(free-layer)

(pinned-layer)

SV SV –– charakterystyki charakterystyki magnetorezystancyjnemagnetorezystancyjne

Antysymetryczna charakterystyka M(H) zakresie małych pól

Duża czułość magnetorezystancyjna

Field [a.u.]-1,5 -1,0 -0,5 0,0 0,5

R [a

.u.]

HFHEB

R↑↑

+ ΔR

R↑↑

FeMn/Ni80Fe20/Cu/Ni80Fe20

( )S

HR

R RR

S

S= ⋅−∂

∂

0

100%

Zależność rezystancji od wzajem-nego położenia wektorów nama-gnesowania:

( )[ ]R RR R

= +−

− −↑↑↓↑ ↑↑

21 1 2cosθ θ

SR ≈8%/Oe

M.Czapkiewicz – praca doktorska (1999)

%16≈Δ

↑↑RR

Write/read head of HDD

GMR & TMR- as read head

GMR & TMR effect can be described as a change of resistance in respect to theangles Θ between magnetizations M of adjacent ferromagnetic layers

( )[ ]R RR R

= +−

− −↑↑↓↑ ↑↑

21 1 2cosθ θ

Disk layer structure

Thin film disks

Substrate – Al Mg (or glass) + electroplated Ni80P20(Tc<Troom). NiP undercoat layer make disk hard and smooth. Cr underlayer is used to control microstructure and magneticproperties the main magnetic recording layer of CoPtCrdoped with B. The magnetic layer is covered by a carbonovercoat layer and lubricant. The last two layers arenecessary for the tribological performance of the head-diskinterface and for the protection of the magnetic layer.

Microscopic propertiesCoercivity Hc - control and modification:• magnetocrystalline anisotropy (grain shape anisotropy),•selection of alloying elements (Al, Cr, Pt, Ta, B,...)•determination of influence:

•deposition conditions and parameters: substrate temperature, biasvoltage, sputtering power (deposition rate), sputtering gas pressure(Ar)•microstructure: film stresses, grain size, texture (grain orientation), grain boundaries, crystal defects.

If the grain structure is noticably voided, leading to reduced magnetic intractions andlower transition noise.

Thermal stabilityFor high density recording the grains are small in comaprison to the bit cell. In a simplified model, assuming isolated grains, the thermally induced switching of magnetization has to overcome anenergy barier. The switching probability f is given by an Arrhenius equation:

⎟⎞

⎜⎛ Δ−=

Wff exp0⎠⎝ kT

ΔW is energy barier, Ku is the uniaxial anisotropy constant, V is grain volume. If the grainsbecome very small, the magnetization switch very easily which leads to superparamagneticefect.

Estimation of minimum grain size (example):

Ku=2×105 J/m3. Bit stored 10 years at room temperature

(f<3.33×10-9Hz at T=300 K), than diameter of spherical grain is 9 nm.

where ΔW = KuV (6)

Granular media vs. patterned media

Antiferromagnetic – coupled (AFC) media

A precise control of the Ru thickness allows to establish an anti-parallel(antiferromagnetic coupling) between two ferromagnetic layers. Decreasing the Mrδin AFC recording media leads to shrap transition, small grains and good S/N.

Mrδ (eff)= Mrδ (top) - Mrδ (bottom) (6)

Storage density of AFC media >25Gbit/in2.

Longitudal recording vs. perpendicular

Perpendicular Recording

Schematic of the perpendicular recording scheme. The soft underlayer in the medium acts as an efficient write field flux path and effectively becomes part of the write head. The transmission electron micrograph (top right) shows a cross-section of a prototype perpendicular recording head used in a recent laboratory demo of 150 Gbit/in2 area recording density.

SV-MTJ Based Read Heads

SV-MTJ as a read sensor for high density (> 100Gb/in2) must fulfill requirements

- Resistance area product (RxA) < 6 Ω-μm2

- High TMR at low RxA

2006 – New world record of TMR

472% Anelva & Advanced Industrial Science and Technology(AIST), Japan

128 Mbit ⇒ 370 mV

Tunneling in FM/I/FM junction

↓↑

↓↑

+−

=II

III nn

nnP

↓↑

↓↑

+−=

IIII

IIIIII nn

nnP

III

III

M

MM

PPPP

III

TMR−

=−

=↑↓

↑↓↑↑

12

↑↑

↑↑↑↓ −=R

RRTMR

↓↓↑↑↑↑ +∝ IIIIIIM nnnnI

↑↓↓↑↑↓ +∝ IIIIIIM nnnnI

↓I↑I

↑I ↓I

FM I (PI) FM II (PII)

Barrier

eVN

EF

Majority Spin Minority Spin

E

DOS

nnN

EF

Majority Spin Minority Spin

E

DOS

nn

EF

Majority Spin Minority Spin

E

DOSNnn

Ni 33 %

Co 42 %

Fe 45 %

Ni80 Fe20 48 %

Co84 Fe16 55 %

CoFeB 60%

Material Polarizations

Our results

Motivation

•How to optimize the multilayers structure of MTJ in order to obtain desirable tunnelling and magneticparametrs?

Structure analysis

•Texture

•Interface roughness

•Correlations between microstructure exchangecoupling and tunnelling parameters of IrMn based MTJs.

Conclusions

MTJ systems for electrical measurements

100×100 μm

10 mm

TIMARIS: Tool status

Tool #1 – process optimization on ∅200 mm wafers since mid of March 03

Tool #2 – The Worlds 1st ∅300 mm MRAM System is Ready for Process in August 03

Multi (10) TargetModule

Oxidation / Pre-clean Module

Transport Module

Clean room

Sputtering System Tohoku

Metal depo.

Plasma Oxidation

LL�: wafer-in

LL�: Bridge Reactive

sputter : surface smooth

Sputtering system Uni Bielefeld

non-magnetic spacer

antiferromagnet

ferromagnet

current conductors

≈ 150 nm

Magnetic Random Access Memory (M-RAM)

M-RAM fabrication compatible to CMOS technology

0

1

Rp - low

Ra - high

SV-MTJ Based Spin Logic Gates

Siemens & Univ. Bielefeld: R. Richter et al. J. Magn.Magn. Mat. 240 (2002) 127–129

SV- MTJ as spin logic gates must fulfill requirements

- Thermal stability- Magnetic stability - Centered minor loop- Single domain like switching behaviour- Reproducibility of R and TMR

RMTJ2

Logic Inputs

Logic Output

Programing Inputs

SV-MTJs

RMTJ3

RMTJ1

RMTJ4

(+, )− IB

(+, )− IA

IS

ISVOUT

VOUT= IS(RMTJ3 + RMTJ3 – RMTJ1 – RMTJ2)

Logic Inputs MTJ 3, MTJ 4

0

2 VOUT

(0,0) (1,1)(1,0)(0,1) (0,0) (1,1)(1,0)(0,1)

MTJ 1 MTJ 2 MTJ 1 MTJ 2

NAND NOR

„1"

„0"Logi

c O

utpu

t

-2 VOUT

Infineon and IBM Present World´s First 16 Mbit MRAM - Innovative Chip Design Results in Highest Density Reported to Date

The increasing number of mobile applications such as smartphones and notebooks with additional multimedia features results in the need for more advanced memory chips.

MRAM is a promising candidate for universal memory in highperformance and mobile computing as it is faster and consumes less power than existing technologies.

A new class of device based on the quantum of electronspin, rather than on charge, may yield the next genera-tion of microelectronics.

Pamięć Parkina

DW – przemieszczane impulsami prądu.

Porównanie ruchu dwóch DW pod wpływem impulsu pola i prądu

Information

Out

side

wo

rd

Input

Output

Information

transmission

Information

Processing

Information

storage

DRAM, MRAM Magnetic(HDD)Optical (CD, DVD)

Flux of information

MAGNETOELECTRONICS

SPIN ENGINEERING SPINTRONICS

Schedule

•Lecture 1 - Fundamentals of magnetism

•Lecture 2 - Spin depend electron transport: AMR, GMR

•Lecture 3 - HDD

•Lecture 4 - Spin depend electron transport: TMR

•Lecture 5 - MRAM

•Lecture 6 - Biosensor, Magnetic wireless actuator for medical applications

•Lecture 7 – Millipede

Fundamentals of Magnetism

Lecture 1

Definitions of magnetic fields

Induction: ( )MHBrrr

+= 0μ

External magnetic field:→

→→

= HM χ

H

Magnetization average magnetic moment ofmagnetic material

Susceptibility tensor representing anisotropic material

→

M

χ

( )→→

=+= HHB μχμ 10

where: ( )χμμ += 10 permability of the material

Maxwell’s equations

0==∇ BdivBrr

or

jHrotHrrrr

==×∇

∫ =l

ildHr

or

tBErotE∂∂

−==×∇r

rrr

Ut

sdBt

ldES

=∂∂

−=∂∂

−= ∫∫φr

orr

or

riHπ2

=

[oe]

[oe]

liNH =

[A/m]

[A/m]

Demagnetization field

poles density, magnetic „charge” density

mMMB

ρμμ

=∇−=⎟⎟⎠

⎞⎜⎜⎝

⎛ −∇

→→→

o

rr

o0

0

Demagnetization field

24

rdVdH πρ

=

rsH /2.0=

⎟⎟⎠

⎞⎜⎜⎝

⎛++−=∇−=

dzdM

dydM

dxdM

M zyxm

ro

rρ

To compute the demagnetization field, the magnetization at all points mustbe known.

MNHd

rr−= when magnetic materials becomes magnetized by application of

external magnetic field, it reacts by generating an opposing field.

[emu/cm4]

The magnetic field caused by magnetic poles can be obtainedfrom:

The fields points radially out from the positive ornorth poles of long line. The s is the pole strengthper unit length [emu/cm2]

[oe= emu/cm3]

Demagnetization tensor N

zzzyzxyzyyyxxzxyxx

π400000000

000020002

ππ

3/40003/40003/4

ππ

π

DStotal HHH −=

For ellipsoids, the demagnetization tensor is the same at all the points within thegiven body. The demagnetizing tensors for three cases are shown below:

The flat plate has no demagnetization within its x-y plane but shows a 4πdemagnetizing factor on magnetization components out of plane. A sphere showsa 4/3 π factor in all directions. A long cylinder has no demagnetization along itsaxis, but shows 2π in the x and y directions of its cross sections.

HS - the solenoid field

(4π)

Exchange coupling

338

2

/1700)1086.2(

2.2)0( cmemuTM BS =

×== −

μ

The saturation of magnetization MS for body-centered cubic Fe crystal canbe calculated if lattice constant a=2.86 Å and two iron atoms per unit cell.

Electron Spin

emum

ehB

201093.04

−×==π

μ

The magnetic moment of spining electron is called the Bohr magneton

3d shells of Fe are unfilled and have uncompensated electron spin magneticmoments

when Fe atoms condense to form a solid-state metallic crystal, the electronicdistribution (density of states), changes. Whereas the isolated atom has 3d: 5+, 1-; 4s:1+, 1-, in the solid state the distribution becomes 3d: 4.8+, 2.6-; 4s: 0.3+,0.3-. Uncompensated spin magnetic moment of Fe is 2.2 μB .

Electron spin

Orbital momentum prL rrr×= ωmrrmvL 2==

2rTeSiL πμ =⋅=Magnetic moment of electron

Tπω 2

=πωπμ

2

2reL =

me

LL

2=

μ)1(

2+= llhL

π

)1(4

+= llm

ehL π

μ

Lr

rr Lμ pr

i

Electron spin

Spin Spin polarizationpolarization ofof ferrmagnetsferrmagnets

Density of states

Energia

d

s

Energy

d

s

Magnetization

Energy

d

sSpin

EF

Spin Polarization, Density of States (DOS)

Ferromagnetic metal (Fe)

↓↑

↓↑

+

−=

nnnn

P

Spin Polarization

Ni 33 %

Co 42 %

Fe 45 %

Ni80 Fe20 48 %

Co84 Fe16 55 %

CoFeB 60%

Material Polarizations

Normal metal (Cu)

EF

Majority Spin Minority Spin

E

DOS

nn

↓↑

↓↑

>>

ρρ)()( FF EnEn

↓↑

↓↑

==

ρρ)()( FF EnEn

N

EF

Majority Spin Minority Spin

E

DOS

nn

Density of states 3d

GMR ⇒ due scattering into the empty quantum statesabove the Fermi level ⇒ ρ ∝D(EF)

„A new class of device based on the quantum of elctron spin, rather than on charge, may yield the next generation of microelectronics.”