Magnetic Tunnel Junction (MTJ)
or
Tunnel Magnetoresistance (TMR)
or
Junction Magneto- Resistance (JMR)
T.Stobiecki
Katedra Elektroniki AGH
11 wykład 13.12.2004
Spin Polarization, Density of States
Density of states 3d
Spin Polarization
Normal metal (Cu)
Ferromagnetic metal (Fe)
E
P 
n  n

n n
E
EF
N
n
EF
n
n

DOS
Material Polarizations
n
Majority Spin Minority Spin
Majority Spin
DOS
Minority Spin
Ni 33 %
Co 42 %
Fe 45 %
Ni80 Fe20 48 %
Co84 Fe16 55 %
CoFeB 60%
n  ( EF )  n  ( EF )
n  ( EF )  n  ( EF )
Tunneling in FM/I/FM junction
FM I (PI)
FM II (PII)
E
E
E
EF
eV
n
EE
F F
N
nn
Barrier
n I  n I
PI  
n I  n I
N
N
n
n n
DOS
Majority Spin Minority Spin
DOS
DOS
Majority Spin Minority
Minority Spin
Spin
I M   nInII  nInII
 
I II
 
I II
I M   n n  n n
TMR 
I
I
I
I M   I M 
2 PI PII

I M 
1  PI PII
R  R
TMR 
R
nII  nII
PII  
nII  nII
I
Type of MTJs
Spin valve junction
(SV- MTJ)
Standard junction
Double barrier junction
FM
FM
FM
I
I
I
FM
FM
FM
AF
I
FM
B
1.2
0.8
1.2
0.8
0.8
0.4
M [T]
M [T]
0.4
0.0
-0.4
M [T]
0.4
0.0
-0.4
0.0
-0.4
-0.8
-0.8
-1.2
-0.8
-1.2
-200
-150
-100
-50
0
H [kA/m]
50
100
150
200
-150
-100
-50
H [kA/m]
0
50
-100
-50
0
H [kA/m]
50
Application-Oriented Properties of S-V MTJ
Materials
SV-MTJ
• I (Al-O,MgO..)
• FM (Co, CoFe, NiFe)
• AF (MnIr, PtMn, NiO)
• Buffer (Ta,Cu, NiFe)
Electric
Treatment
Preparation
• Sputtering deposition
• Annealing
• Field cooling
• Oxidation
Magnetic
• Interlayer coupling field HS
• Tunnel Magnetoresistance -TMR
• Exchange bias field HEXB
• Resistance area product -RxA
• Coercive field pinned HCP
and free HCF layer
• Switching field HSF
Magnetic and Electric Parameters
FM I (Free)
I
Interlayer coupling
HS
FM II (Pinned)
Exchange coupling
HEXB
AF
B
50
1.2
HCF
0.8
40
HS
TMR [%]
M [T]
0.4
0.0
HCP
HEXB
30
TMR 
R  R
R
20
-0.4
10
-0.8
HSF
-1.2
0
-150
-100
-50
H [kA/m]
HSF switching fields
0
50
-160
-120
-80
-40
H [kA/m]
0
40
80
Applications of SV-MTJ
SENSORS
M-RAM
SV-MTJ
SPIN-LOGIC
READ HEADS
SV-MTJ Based MRAM
Memory Cell
Memory Matrix
IB
Bit lines
SV-MTJ
Reading current
IB
IR
Writing “1”
IW
Writing “0”
Writing - rotation of the free layer
IW
SV- MTJ as MRAM component must fulfill
requirements
- Thermal stability
- Magnetic stability
- Single domain like switching behaviour
- Reproducibility of RxA, TMR and Asteroids
Reading - detection of a resistance of a
junction
Critical switching fields Hx , Hy (S-W) asteroid
1
Hy/H(0)
Word lines
0
Motorola: S.Tehrani et al. PROCEEDINGS OF THE IEEE, VOL. 91, NO. 5, MAY 2003 -1
-1
0
1
- Non-volatility of FLASH with fast programming, no program endurance
Features of M-RAM
limitation
- Density competitive with DRAM, with no refresh
- Speed competitive with SRAM
- Nondestructive read
- Resistance to ionization radiation
- Low power consumption (current pulses)
• Single 3.3 V power supply
• Commercial temperature range (0°C to 70°C)
• Symmetrical high-speed read and write with fast access time (15, 20 or 25 ns)
• Flexible data bus control — 8 bit or 16 bit access
• Equal address and chip-enable access times
• All inputs and outputs are transistor-transistor logic (TTL) compatible
• Full nonvolatile operation with 10 years minimum data retention
Motorola: S.Tehrani et al. PROCEEDINGS OF THE IEEE, VOL. 91, NO. 5, MAY 2003
SV-MTJ Based Spin Logic Gates
VOUT= IS(RMTJ3 + RMTJ3 – RMTJ1 – RMTJ2)
(+,  ) IA
Logic Inputs
(+,  ) IB
NAND
RM TJ3
MTJ 2
MTJ 1
MTJ 2
RM TJ 4
2 VOUT
IS
SV-MTJs
Programing Inputs
RM TJ2
VO UT
IS
Logic Output
Logic Output
RM TJ1
MTJ 1
NOR
„1"
0
„0"
-2 VOUT
(0,0)
SV- MTJ as spin logic gates must fulfill requirements
- Thermal stability
- Magnetic stability
- Centered minor loop
- Single domain like switching behaviour
- Reproducibility of R, TMR
Siemens & Univ. Bielefeld: R. Richter et al. J. Magn.Magn. Mat. 240 (2002) 127–129
(0,1) (1,0) (1,1) (0,0) (0,1) (1,0) (1,1)
Logic Inputs MTJ 3, MTJ 4
Features of Spin Logic Gates
- Programmable logic functions (reconfigurable computing)
- Non-volatile logic inputs and outputs
- Fast operation (up to 5 GHz)
- Low power consumption
- Compatibility to M-RAM
SV-MTJ Based Read Heads
SV-MTJ as a read sensor for high density (> 100Gb/in2)
must fulfill requirements
- Resistance area product (RxA) < 6 -m2
- High TMR at low RxA
A MTJsExperiments on SV -MTJs
B MTJs
Ta 5 nm
Au 25 nm
NiFe x nm
Ta 3 nm
CoFe 2.5 nm
Junction
Cu 30 nm
0
10
30
60
100
Al2O3 1.4 nm
Junctions size
(180180) m2
CoFe 2.5 nm
Ta 5 nm
MnIr 10 nm
NiFe 3 nm
Cu 5 nm
Junction
Al2O3 1.4 nm
CoFe t nm
MnIr 12 nm
3
6
10
30
50
NiFe 2 nm
Ta 5 nm
Cu 10 nm
Cu 25 nm
Ta 5 nm
Substrate Si (100)
SiO2
Substrate Si
(100)
A structure prof. G. Reiss laboratory University Bielefeld
B structure prof. T. Takahasi laboratory, Tohoku University
10 mm
Effect of Annealing on TMR
As deposited
Annealed
50
14
TMR = 13.4 %
TMR = 48 %
12
40
TMR [%]
TMR [%]
10
8
6
30
20
4
10
2
0
-150
-100
-50
0
H [kA/m]
50
100
0
150
-120
-80
-40
0
40
80
120
H [kA/m]
40
100 nm (10 sec)
100 nm (13 sec)
100 nm (16 sec)
10 nm (10 sec)
10 nm (13 sec)
10 nm (16 sec)
35
H=80 kA/m
30
TMR [%]
25
20
15
10
10 mm
5
annealing 1 hour in vacuum
10-6 hPa
0
100
150
200
250
300
o
Annealing temperature ( C)
350
Interlayer and Exchange Coupling Fields
3
1.2
3nm
6nm
10nm
30nm
50nm
2
10 nm
30 nm
60 nm
100 nm
1.0
0.8
0.6
1
Kerr rotation [min]
Kerr rotation [min]
Interlayer coupling fields
B MTJs
Exchange coupling fields
A MTJs
0
-1
0.4
0.2
0.0
-0.2
-0.4
-0.6
-2
-0.8
-3
-100
-75
-50
-25
0
25
50
-1.0
-3000 -2500 -2000 -1500 -1000
-500
0
500
1000
1500
H [A/m]
H [kA/m]
50
3nm
6nm
10nm
30nm
50nm
30
10 nm
100 nm
30
TMR[%]
TMR [%]
40
40
20
20
10
10
0
0
-100
-75
-50
-25
H [Oe]
0
25
50
-3000
-2000
-1000
0
H [Oe]
1000
2000
3000
Interlayer and Exchange Coupling
Fields
H EXB
J EXB

0 M P tP
Js
HS 
0 M F tF
60
-6
2
MOKE
R-VSM
TMR
JEXB= 249 x10 J/m
50
1000
HS, as dep.
0
800
HS, 300 C
600
J = 1.04x10 [J/m ]
-5
2
J = 0.75x10 [J/m ]
-5
HS [A/m]
HEXB[kA/m]
40
30
20
10
2
400
200
Hs~1/tf
0
0
0
10
20
30
CoFe [nm]
40
50
0
20
40
60
tNiFe+CoFe [nm]
80
100
Temperature Dependence of TMR
60
0
50
t=100nm (270 C)
30k
50k
70k
100k
150k
200k
250k
300k
30
20
G P  G AP
TMR 
G AP
30
20
10
10
0
-20
-15
-10
-5
0
5
10
H [Oe]
15
0
-40
20
-30
-20
-10
0
H [Oe]
dG(T )  GP (T )  G AP (T )
54
52
1.30
50
1.25
dG Normalized
TMR [%]
TMR[%]
40
30K
50K
70K
100K
150K
200K
250K
300K
40
TMR [%]
50
0
t=10nm (300 C)
48
46
44
42
t = 10 nm (3000 C)
t = 100 nm (2700 C)
40
38
o
t = 10 nm (300 C)
t = 100 nm (270o C)
1.20
1.15
1.10
1.05
1.00
36
0.95
50
100
150
200
250
300
50
100
T [K]
P. Wiśniowski, M.Rams,... Temperature dependence of tunnel magnetoresistance of IrMn based MTJ, phys. stat. sol (2004)
150
T [K]
200
250
300
10
20
Total Conductance
G(1, 2 , T )  GT (T )[1  P1 (T ) P2 (T ) cos(1   2 )]  GSI (T )
GAP (T )  GT (T )[1  P1 (T ) P2 (T )]  GSI (T )
TMR 
GP (T )  GT (T )[1  P1 (T ) P2 (T )]  GSI (T )
G P  G AP
G AP
dG(T )  GP (T )  GAP (T )  2GT (T ) P1 (T ) P2 (T )
GT (T )  G0CT / sin(CT )
Varies slightly with T
Negligible
P1(T ) P2 (T )  P01(1  b1T 3 / 2 ) P02 (1  b2T 3 / 2 )
Varies with T as magnetization does Bloch law
Dominant
Polarization, Bloch Law
dG(T )  2GT (T ) P1 (T ) P2 (T )
M (T )  M 0 (1  BT 3 / 2 )
1. Set H= – 2000 Oe
dG(T)/dG(30 K)
1.00
0.99
1. Set H= – 2000 Oe
2. Cooling H= 500 Oe
2. Cooling H= –500 Oe
3. Measured M (T)
3. Measured M (T)
0.98
-2000
0.97
-1000
0
1000
H [Oe]
2000
3000
1,02
100
150
T [K]
200
250
P
1,00
300
M Normalized
50
0,98
0,96
AP
0,94
0,92
P01  48 [%] b1  1.0 10
6
[K
3 / 2
]
P02  45 [%] b2  9.2 10 6 [ K 3 / 2 ]
100 nm
0,90
0
50
100
150
T [K]
200
250
B  6.76  106 [ K 3 / 2 ]
B  6.99  10 6 [ K  3 / 2 ]
300
Spin Independent Conductance
GSI  (GP  GAP ) / 2  GT
0.035
0.030
GSI  NT 
GSI [S]
0.025
0.020
0.015
0.010
N  3.21 10 6 [ SK  ]
0.005
  1.66
0.000
50
100
150
T [K]
200
250
300
Hopping conductance, low level of defects
N  2.0 10 6 [ SK  ]
  1.33
Hopping conductance, high level of defects
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
Clean room
Multi (10) Target
Module
Oxidation /
Pre-clean Module
Transport Module
Sputtering System
LL１: wafer-in
Plasma
Oxidation
LL２:
Bridge
Metal
depo.
Reactive
sputter :
surface smooth
Measurements
MOKE
R-VSM
MOKE with Orthogonal Coils
Hx coils
Hy coils
Sample