Tomasz Stobiecki AGH Katedra Elektronikilayer.uci.agh.edu.pl/T.Stobiecki/dydaktyka/... · notebooks...
Transcript of Tomasz Stobiecki AGH Katedra Elektronikilayer.uci.agh.edu.pl/T.Stobiecki/dydaktyka/... · notebooks...
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.”