Magnetic Spin Devices: 7 years from Lab to Product ... · Jim Daughton, NVE Corporation Magnetic...
Transcript of Magnetic Spin Devices: 7 years from Lab to Product ... · Jim Daughton, NVE Corporation Magnetic...
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Jim Daughton, NVE Corporation
Magnetic Spin Devices:7 Years From Lab To Product
Boston, MA December 1, 2004
Symposium X, MRS 2004 Fall Meeting
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• “Early Discoveries” - 1988 to 1995• Resulting Products – Potential Products• “New Discoveries” - 1996-2004• Future Products
Outline of PresentationOutline of Presentation
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Giant Giant MagnetoresistanceMagnetoresistance (1988)(1988)
• Simultaneous Discovery– Fert (France)– Grunberg (Germany)– Multi-Layer Devices– Ferromagnetic Materials
• Previous Magnetoresistance Materials– Anisotropic Magnetoresistance– ~ 2% Magnetoresistance R.T. Thin Films– Current Direction
• Much Higher Magnetoresistance Observed
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• Magnetic Layers AF Coupled• Antiparallel - High Resistance• Magnetic Field Overcomes
Coupling
• Parallel - Low Resistance
NVE GMR Multilayer CrossNVE GMR Multilayer Cross--SectionSection
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Typical CharacteristicTypical Characteristic
3.6
3.7
3.8
3.9
4
4.1
4.2
-400 -200 0 200 400applied field (Oe)
resi
stan
ce (k
ohm
)
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New Outlook For New Outlook For MagnetoresistanceMagnetoresistance
• Conduction Electrons In FM’s - Polarized– Same Direction - “Spin Up”– Opposite Direction to M - “Spin Down”
• “Spin Up” Electrons - A Longer MFP• “Spin Down” Electrons - Shorter MFP
Conduction Between Ferromagnetic Bodies Depends On How They Are Magnetized.
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Spin Valve (1990Spin Valve (1990))
High Coercivity FM LayerCopper
Low Coercivity FM Layer
II
• Antiparallel M’s - Higher Resistance• Parallel M’s - Lower Resistance• Magnetoresistance ~ 6% Initially• Easy to Switch “Soft” Layer
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Pinning With An AntiPinning With An Anti--FerromagnetFerromagnet
Substrate
Ferromagnet
Anti-Ferromagnet
Coupling Interface
• Cool To Below Neel Temperature In A Field• Ferromagnet Can Be “Pinned” To High Fields
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Synthetic Synthetic AntiferromagnetAntiferromagnet (SAF)(SAF)
Ferromagnet
Ferromagnet
6-10 A Ruthenium
• Thin Inner Layer of Certain Materials (Ru)• Very High Antiparallel Coupling (~2500 Oe)• Pin One FM Layer - Really Pinned M’s
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Tunneling Tunneling MagnetoresistanceMagnetoresistance (1995)(1995)
• Practical Devices - Moodera, Miyizaki• Much Higher Magneto-Resistance
ParallelMagnetizations
Anti-ParallelMagnetizations
LowerResistance
LowerResistance
HigherResistance
LowerTunneling
Current
HigherTunneling
Current
Insulator
InsulatorConductor
ConductorMagnetic Film
Magnetic Film
Magnetic Film
Magnetic Film
Magnetic Film
Magnetic Film Magnetic Film
Magnetic Film
ElectronMotion
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GMR Bridge Sensor (Two Shown) GMR Bridge Sensor (Two Shown) -- 19951995
GMR Resistors (In Gap)
Shielded ResistorsWire Bonding Pads
Flux Concentrators
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GMR Read Heads (1996)GMR Read Heads (1996)
• Most Commercial Heads - Tsang et al (IBM,1994)– Spin Valves - Pinned and Soft Layer– Pinned Layer Magnetization Across Stripe– Senses Vertical Fields
• New Additions - Pinned SAF and NOL
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GMR Isolators (1998)GMR Isolators (1998)
• Spin Valve Sensor• Used For Ground Isolation
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MRAM ConceptMRAM Concept
• Magnetic Hysteresis For Data Storage– Material Properties - Anisotropy, Coercivity– Shape
• Magnetoresistance of Storage Element -Readout
• Magnetic Elements on Integrated Circuit• Advantages
– Doesn’t Wear Out With Writing (Unlike Flash)– Nonvolatile (Unlike SRAM or DRAM)– Writes Fast (Unlike Flash)
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GMR MRAM PseudoGMR MRAM Pseudo--Spin ValveSpin Valve
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TMR MRAMTMR MRAM
Motorola Figure
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MRAM Products (2004?)MRAM Products (2004?)
• Many Developers - Two Near Products
• Motorola (Freescale)– Samples 2003– Limited Production Y/E 2004 or 2005– 4 Mbit Capacity
• Cypress Semiconductor– Samples - Early 2005– 256K bit Capacity
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MRAM Scaling ChallengeMRAM Scaling Challenge
• Stability Requires Es/kT >~50:1• Small Volume → High Energy Density• Write Currents Get Big (Conventional Designs)
– Transistors Are Big (~2 X 5mA)– Heating in Narrow Conductors
Year 2003 2005 2007 2010Lithography (µm) 0.1 0.08 0.07 0.05Cell Size (µm2) 0.06 0.04 0.03 0.01Capacity (bits) 1G 2G 4G 8G
• Road Map Projections
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Still Higher TMRStill Higher TMR
Parkin et. al.,
Nature (2004)
• Over 200%• Challenges
Understanding of TMR– 2P1P2/1 - P1P2
– Believed P1, P2Understood
– Obviously Overconfident
• Large On-Off Ratios Possible!!
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Spin Momentum Transfer (SMT)Spin Momentum Transfer (SMT)
5.1
5.3
5.5
0 600 1200Magnetic Field [G]
dV/d
I [O
hm]
130 nm
5.1
5.3
5.5
-1 -0.5 0 0.5 1Current [mA]
dV/d
I [O
hm]
Py (2 nm)
Py (20 nm)Cu (6 nm)
Cu
Cu
free layerfixed layer
70 nm
Bob Buhrman, Dan Ralph, et.al. Cornell
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Spins in Semiconductors (SPINS)
• Ferromagnetic Semiconductors • Light-Induced Spin• LED Sensing• Ferromagnetic Injection
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Thermally Assisted MRAMThermally Assisted MRAM
Chip Operating TemperatureRequired Thermal RiseWrite
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Two Methods For TTwo Methods For T--MRAMMRAM
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Possible ImplementationPossible Implementation
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SMT Written MRAMSMT Written MRAM
5.1
5.3
5.5
0 600 1200Magnetic Field [G]
dV/d
I [O
hm]
130 nm
5.1
5.3
5.5
-1 -0.5 0 0.5 1Current [mA]
dV/d
I [O
hm]
Py (2 nm)
Py (20 nm)Cu (6 nm)
Cu
Cu
free layerfixed layer
70 nm
Bob Buhrman, Dan Ralph, et.al. Cornell
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Spin Waves Spin Waves -- Spin Transfer OscillatorSpin Transfer Oscillator
6.5 7.0 7.5 8.0 8.5
0.0
0.5
1.0
1.5
8.5 mA
7.5 mA
6.5 mA
5.5 mA
4.5 mA
4.0 mA
Am
plitu
de (n
V/H
z1/2 )
Frequency (GHz)
point contact
radiating spin-waves
H
e-precessional excitation
2r
Polarizing layer (thick): “Fixed” Active layer (thin): “Free”
W. H. Rippard et al PRL 92, 027201 (2004)
Review of metal based spintronics: Review of metal based spintronics: Stephen Stephen RussekRussek
Absorbed angular momentum:Torque
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Future ProductsFuture Products
• High Density MRAM- Will Scale– Thermally Assisted Writing– Spin Momentum Transfer
• Magnetic Logic - High On/Off Ratio TMR• SPINS Program (Spins In Semiconductors)
– Semiconductor/Light– Spin Transfer Oscillator– Magnetic Transistor- Storage