perpendicular magnetic multilayers for advanced memory … · 2017-06-09 · pma (perpendicular...
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© 2012 HGST, a Western Digital company
© 2012 HGST, a Western Digital company
Sangmun Oh; Zheng Gao
Kochan Ju; Lijie Guan
HGST Wafer Development Team
Perpendicular Magnetic Multilayers
for Advanced Memory Application
© 2012 HGST, a Western Digital company
Magnetic thin film and Spintronics
Magnetic thin film is used for data storage and memory applications
PMA (Perpendicular magnetic anisotropy) is fundamental building block for memory devices.
Tunneling magneto resistance (TMR) for both storage and memory applications
High MR ratio with MgO coherent tunneling is required for both applications
Perpendicular magnetic properties of pinned and free layer are also essential for advanced
storage/memory
High anisotropy PMA pinned layer
[Co/Pt] multilayer
[Co/Pt]/Ru/[Co/Pt] SAF structure PMA
Thermal Stability
Integrated STT-MRAM stack PMA and its performance
Sangmun Oh (AVS meeting-Dec/16/2014)
Outline
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Magnetic thin film for data storage
Prof. ohno (Tohoku Univ)
Magnetic thin film is used for storage industry
Perpendicular magnetic anisotropy (PMA) is used in many area
Reader head
Writer head
Media
EVERSPIN
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Magnetic thin film (GMR) Nobel Prize in Physics 2007
Albert Fert Peter Grünberg
For the discovery of Giant Magneto-Resistance.
Independently discovered by Albert Fert and
Peter Grünberg in Fe/Cr multilayers in 1988
- Phys. Rev. Lett. 61, 2472 (1988)
- Phys. Rev. B 39, 4828 (1989)
First product using
a GMR read head shipped in 1998
IBM 18 GB Ultrastar drive
Remarkable enhancement of recording density
Spintronices & nanotechnology
Ferromagnetic/Non-magnetic
© 2012 HGST, a Western Digital company
Tunneling Magnetoresistance (TMR)
Coherent tunneling with MgO barrier
W. Burtler PRB63
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Amorphous CoFeB
Amorphous CoFeB
Polycrystalline CoFeB (001)
Polycrystalline CoFeB (001)
Poly crystal MgO (001) Poly crystal MgO (001)
APL 86, 092502 (2005)
Anelva & AIST
Pre-anneal Post-anneal
FL
RL
High signal can be achieved from
Highly spin polarized magnetic interfaces
Spin-filter effects in tunnel barrier
MgO barrier Reader sensor with CoFeB/MgO/CoFeB
1100% (4.2K) TMR at CoFeB/MgO/CoFeB MTJ
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Perpendicular TMR with CoFeB/MgO interface
(Prof Ohno, Tohoku Univ)
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Polycrystalline CoFeB (001)
Polycrystalline CoFeB (001)
Poly crystal MgO (001)
FL
RL
Poly crystal MgO (001)
FL
RL
High Magnetic anisotropy (high Hk) Thermally stable
Negative shape anisotropy Easy magnetization switching
Perpendicularly magnetized films
L10 ordered alloy films such as FePt, FePd, _Require high Tem deposition
(Bulk PMA_high damping & poor band/lattice matching with MgO)
RE-TM amorphous alloy films such as TbFeCo
(Thermally not stable at high Tem >200C)
Metallic mutlilayers or ultrathin films
such as Ni/Co, Co/Pt, CoFeB/MgO, (Interface PMA)
Perpen magnetization anisotropy (PMA)-material
In-plane Out of-plane
Perpendicularly magnetized films property
How to make?
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Fe
O MgO-2P
Fe-3d
Interfacial Perpendicular anisotropy (i-PMA)
Fe-O hybridization
of atomic orbital
Elastic stress due to
lattice distortion
Interface asymmetry due to
Crystal symmetry breaking
Vacuum / Fe interface
Phys. D: Appl. Phys.
46 (2013) 074001
(A) (B) (C)
© 2012 HGST, a Western Digital company© 2012 HGST, a Western Digital company 10
[Co/Pt]
[Co/Pd]
[Co/Ni], [Co/Pd], [Co/Pt] from many papers
Interface driven perpendicular system[Co/Ni]
Interface Perpendicular anisotropy system
© 2012 HGST, a Western Digital company
Magnetic thin film and Spintronics
Magnetic thin film is used for data storage and memory applications
PMA (Perpendicular magnetic anisotropy) is fundamental building block for memory devices.
Tunneling magneto resistance (TMR) for both storage and memory applications
High MR ratio with MgO coherent tunneling is required for both applications
Perpendicular magnetic properties of pinned and free layer are also essential for advanced
storage/memory
High anisotropy PMA pinned layer
[Co/Pt] multilayer
[Co/Pt]/Ru/[Co/Pt] SAF structure PMA
Thermal Stability
Integrated STT-MRAM stack PMA and its performance
Sangmun Oh (AVS meeting-Dec/16/2014)
Outline
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Struc Thk(A) Repeat
Ta 40 1
Pt Y
Co X
Pt 20 1
Ta 20 1
N
Strain-induced PMA at the interface-[Co/Pt] system Alloying Pt atom become polarized by Co atom in their vicinity Keff (erg/cc) was calculated to evaluate PMA Optimized x, y, N is crucial for narrow switching distributionIf Co too thinsuperpara, too thickin-plane or multi-domain
thus, optimization of Co thickness is needed.
Perpendicular Multilayers
Co/Pt Perpendicular Multilayers
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Pt/Co Interface- Source of PMA
Co/Pt - Flat Interface and Uniform Coverage
Hk Determined by Co & Pt Ratio
Thicker Co Buffer Prevent Pt Diffusion
If Pt is too thin, then Co cannot be separated
[Co5
/Pt3
]*5
[Co3
/Pt5
]*5
[Co3
/Pt8
]*5
[Co2
/Pt3
]*5
[Co2
/Pt2
]*5
[Co5
/Pt5
]*5
[Co4
/Pt4
]*5
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
X Axis Title
Hk (
Oe
)
0.0
5.0x105
1.0x106
1.5x106
2.0x106
2.5x106
3.0x106
3.5x106
4.0x106
4.5x106
Ke
ff (erg
/cc)
Perpendicular Multilayers
Co/Pt Perpendicular Multilayers
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
JAP 103, 07A917 (2008)PRB 71, 224403 (2005)
As N increases, Hc increases with rectangular shape
And then Hc decreases with unfavorable shearing of loop
Increase of roughness can be a reason?
Gradual switching
Thin Pt can not separate two Co
i-PMA is weak
Perpendicular Multilayers
Multi-domain structure
Roughness
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
-1200-1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200
-0.0015
-0.0010
-0.0005
0.0000
0.0005
0.0010
0.0015P
erp
en
dic
ula
r M
Field (Oe)
[Co5A/Pt3A]*1
[Co5A/Pt3A]*2
[Co5A/Pt3A]*3
[Co5A/Pt3A]*4
[Co5A/Pt3A]*5
[Co5A/Pt3A]*8
[Co5A/Pt3A]*10
Hc Increases with Repeat and Saturate. If N Larger than 8, Multi-Domain Behavior
Perpendicular Multilayers
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Perpendicular Multilayers
400C
280C300C
350C
400C
Co/Pt Multilayer Hc Stable to 400C (Co/Pt) SAF Structure Stable upto 400C
© 2012 HGST, a Western Digital company
Magnetic thin film and Spintronics
Magnetic thin film is used for data storage and memory applications
PMA (Perpendicular magnetic anisotropy) is fundamental building block for memory devices.
Tunneling magneto resistance (TMR) for both storage and memory applications
High MR ratio with MgO coherent tunneling is required for both applications
Perpendicular magnetic properties of pinned and free layer are also essential for advanced
storage/memory
High anisotropy PMA pinned layer
[Co/Pt] multilayer
[Co/Pt]/Ru/[Co/Pt] SAF structure PMA
Thermal Stability
Integrated STT-MRAM stack PMA and its performance
Sangmun Oh (AVS meeting-Dec/16/2014)
Outline
© 2012 HGST, a Western Digital company Sangmun Oh (AVS meeting-Dec/16/2014)
Spin torque Switching for PMA TMR Stack
Bottom Pin MTJ with CoFeB
Electrode
SAF Co/Pt High Hc Pinned Layer
Stray Field Balancing
PMA Free Layer Maximized with
double MgO capping
STT-Magnetization reversal by
switching current
FREE MgO PIN
a) STT-switching R(AP)R(P)
b) STT-switching R(P)R(AP)
Torque
Torque
© 2012 HGST, a Western Digital company
Successfully Demonstrate PMA Spin Torque Switching
Repeatable Switching is Demonstrated
PMA TMR Stack and Spin Torque Switching
Jc ~3.7MA/cm2
Sangmun Oh (AVS meeting-Dec/16/2014)
© 2012 HGST, a Western Digital company
Summary
Demonstrated Robust pMA TMR Pinned Layer Magnetic
Properties Stable Upto 400C
Demonstrated Repeatable Switching by voltage
Thank You
Sangmun Oh (AVS meeting-Dec/16/2014)
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