Jim Daughton, NVE Corporation

Magnetic Spin Devices:7 Years From Lab To Product

Boston, MA December 1, 2004

Symposium X, MRS 2004 Fall Meeting

• “Early Discoveries” - 1988 to 1995• Resulting Products – Potential Products• “New Discoveries” - 1996-2004• Future Products

Outline of PresentationOutline of Presentation

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

• Magnetic Layers AF Coupled• Antiparallel - High Resistance• Magnetic Field Overcomes

Coupling

• Parallel - Low Resistance

NVE GMR Multilayer CrossNVE GMR Multilayer Cross--SectionSection

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

)

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.

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

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

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

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

GMR Bridge Sensor (Two Shown) GMR Bridge Sensor (Two Shown) -- 19951995

GMR Resistors (In Gap)

Shielded ResistorsWire Bonding Pads

Flux Concentrators

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

GMR Isolators (1998)GMR Isolators (1998)

• Spin Valve Sensor• Used For Ground Isolation

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)

GMR MRAM PseudoGMR MRAM Pseudo--Spin ValveSpin Valve

TMR MRAMTMR MRAM

Motorola Figure

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

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

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!!

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

Spins in Semiconductors (SPINS)

• Ferromagnetic Semiconductors • Light-Induced Spin• LED Sensing• Ferromagnetic Injection

Thermally Assisted MRAMThermally Assisted MRAM

Chip Operating TemperatureRequired Thermal RiseWrite

Two Methods For TTwo Methods For T--MRAMMRAM

Possible ImplementationPossible Implementation

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

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

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