1 High Sensitivity Magnetic Field Sensor Technology overview David P. Pappas National Institute of Standards & Technology Boulder, CO.

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High Sensitivity Magnetic Field Sensor Technology overview

David P. Pappas

National Institute of Standards & Technology

Boulder, CO

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Market analysis - magnetic sensors 2005 Revenue Worldwide - $947M

Growth rate 9.4%

TypeApplicationHT SQUID,

$0.38M

LT SQUID, $5.3M

Magnetometer

$5.5M

Compass, $4.8M

Position sensor, $3.4M

GMR, $40.2M

AMR $121.6M

Hall element, $94.7M

Hall IC, $671.2M

“World Magnetic Sensor Components and Modules/Sub-systems Markets”Frost & Sullivan, (2005)

Medical $24M

Other$11M

AerospaceDefense

$37M

Industrial, $156M

Auto$338M

Computer, $380M

Research, $0.8M

NDE $0.1M

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Outline

High sensitivity applications & signal

measurements

Description of various types of

sensors used

New technologies

Comparison and analysis of sensor

metrics

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Applications

Health Care

Geophysical

Astronomical

Archeology

Non-destructive

evaluation (NDE)

Data storageNorth Caroline Department of Cultural Resources

“Queen Anne’s Revenge” shipwreck site Beufort, NC

Mars Global Explorer (1998)

Magnetic RAM

SI units

Magneto-encephalography

Magneto-Cardiography

“Biomagnetism using SQUIDs: Status and Perspectives” Sternickel, Braginski, Supercond. Sci. Technol. 19 S160–S171 (2006).

Bio-magnetic tag detection

Frietas, ferreira, Cardoso, CardosoJ. Phys.: Condens. Mater 19, 165221 (2007)

JPL - SAC-C missionNov. (2000)

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SI - Le Système International d’Unitès

I (A)r (m)

“Magnetic field intensity”: H-field A/m

B = flux density

= “Magnetic induction” field

Frequency

• What do we measure?

Use 0 = permeability of free space

B = 0 H

B-field tesla (T) kg/(As2)

H = ~0.1 A/m

B = 210-7 Te.g. 1 A @ 1 m

A

dt

dV

= BA

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B-field Ranges & Frequencies

Adapted from “Magnetic Sensors and Magnetometers”, P. Ripka, Artech, (2001)

1 fT

1 nT

1 100 10,0000.010.0001Frequency (Hz)

Mag

netic

fiel

d R

ange

1 pT

Geophysical

Industrial

MagneticAnomaly

Magneto-cardiography

Magneto-encephalography

1 fT

1 100 10,0000.010.0001Frequency (Hz)

B-f

ield

1 pT

Geophysical Industrial/NDE

MagneticAnomaly

Magneto-cardiography

Magneto-encephalography

1 nT

1 gauss 10-4 T ~ Earth’s B-field1 mT

effects

1 T1 A @ 1 m

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B-fields… Induce voltages

Affect scattering of electrons in matter

Change phase of currents flowing in

superconductors

Create energy level splittings in atoms

=> Use these effects to build a toolbox for field detection in important applications

Technologies

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Magnetometer technologies Induction

Search Coil Fluxgate Giant magneto-impedance

Scattering Anisotropic magneto-resistive (AMR) Spintronic – Giant MR, Tunneling MR, Spin Xtor… Hall Effect Magneto-optical

Superconducting SQUIDS

Spin Resonance Proton, electron

State

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State measurement Low noise excitation source -

Voltage, current, light, …

Detector volume - = Ah

Sense state

Flux feedback is typical

Linearize

Dynamic Range

Complicated

Limits slew rate & bandwidth

Bext

Bf

B

S

Noise

SA

h

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Noise metrology Magnetically shielded container

(or room)

Low noise preamplifiers

Spectrum analyzer – P = V2/Hz field noise = power / sensitivity

StateMeasurement

Low TCSQUIDmagnetometer(w/gradiometer)

Hz0.01 0.1 1 10 100

1

10

100

1,000

10,000

100,000

f T

/H

z

Benchmarks

1/f

White

HzT

TV

HzV

2

Units

Preamp

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Benchmark properties:

SQUID

State variable V, f, etc

B-field measurement Vector/scalar

Bnoise - Noise @ 1 Hz T/Hz

Detector volume ( ) cm3-mm3

Operating temperature, T Cryogenic/RT/heated

Power – form factor Line/Battery

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Superconducting Quantum Interference Devices

IL IR

I

TunnelJunctions

B

Left-Right phase shifted by B

Signal

PU loop

Superconductor

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Pickup loops for SQUIDS

One loop: measure BZ

Two opposing loops: dBZ/dz (1st order gradiometer)

Good noise rejection

Opposing gradiometers: dBZ

2/dz2 (2nd order gradiometer)

High noise rejection

N

SSQUID specs

Z

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SQUID Magnetometer

“The SQUID Handbook,” Clarke & Braginski, Wiley-VCH 2004

Commercial: 10 – 100’s k$

MKG

Discretecomponents

IntegratedSystems

State variable Voltage (10’s V)

B-field Vector, gradients

Bnoise @ 1 Hz ~10 fT/Hz

- Volume ~ 1 cm3 coil

Operating T cryogenic

Power Line

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Real time magneto-cardiographywith SQUID magnetometer

Oh, et. al JKPS (2007)

~60 pT

Resonance

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Resonance magnetometers

Nuclear spin resonance Protons

water, methanol, kerosene

Overhauser effect: He3, Tempone

Electron spin resonance He4,Alkali metals (Na, K, Rb)

Bext

f Bext

Proton

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Proton magnetometer

Commercial: 5 k$

• Kerosene cell•Toroidal excitation& pickup

Olsen, et. al (1976)From Ripka, (2001)e- spin

State variable Frequency ~ kHz

B-field Scalar

Bnoise @ 1 Hz

sources

~10 pT/Hz

depolarization

- Volume 1 cm3 cell

Operating T -20 => 50 oC

Power Battery

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Electron spin magnetometers

Vapor cell

Photodetector

Bext

RFCoils

/4 Filter

Laser

Budker, Romalis, Nature Physics, 3(4), 227-234 (2007)He4

f~ MHzfor e-

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He4 e--spin magnetometer

JPL - SAC-C missionNov. (2000)

Smith, et al (1991)from Ripka (2001)CSAM

State variable Frequency

B-field vector/scalar

Bnoise @ 1 Hz 1 pT/Hz

- Volume ~10 cm3 cell

Operating T ambient

Power battery

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e--spin magnetometer Chip scale atomic magnetometer

P. D. D. Schwindt, et al. APL 90, 081102 (2007).

Rb metal vapor

Optimized for low power

Very small form factor

4.5 mm

SERF

State variable Frequency

B-field Scalar

Bnoise @ 1 Hz 5 pT/Hz

- Volume 20 mm3

Operating T 110 oC

Power Small battery

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e--spin magnetometer Spin-exchange relaxation free

Kominis, et. al, Nature 422, 596 (2003)

K metal vapor

Low field, high density of atoms

Line narrowing effect

All-optical excitation & pickup

=>Optimized for high sensitivity

Solid state

State variable Frequency

B-field Vector

Bnoise @ 1 Hz 0.5 fT/Hz

- Volume ~ 3 cm3

Operating T 180 oC

Power line

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Solid state magnetometers Inductive

Fluxgate Giant magneto-impedance

Magneto-resistive AMR – Anisotropic MR

Spintronic GMR – Giant MR TMR – Tunneling MR

Disruptive technologies Hybrid superconductor/solid state Magneto-striction Magneto-electric Spin Transistors

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Fluxgate

M

H

Bext

Hmod(f)

MState variable Inductive 2f

B-field Vector

Bnoise @ 1 Hz

Sources

<10 pT/Hz

Thermal magneticJohnsonPerming

- Volume ~1 cm3

Operating T RT

Power battery

“Magnetic Sensors and Magnetometers” P. Ripka, Artech, 2001

Commercial: ~1 k$

Pickup(2f)Drive(f)

FG innov.

Bext

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Innovations in Fluxgate technology

Apply current in core

Single domain rotation

100 fT/Hz @ 1 Hz

Circumferential Magnetization

IM

Planar fabrication

80 pT/Hz @ 1 Hz

Micro-fluxgates

Koch, Rosen, APL 78(13) 1897 (2001) Kawahito S., IEEE J. Solid State Circuits 34(12), 1843 (1999)

GMI

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Giant Magneto-impedance (GMI)

“Giant magneto-impedance and its applications”Tannous C., Gieraltowski, Jour Mat. Sci: Mater. in Electronics, V15(3) pp 125-133 (2004)

Magnetic amorphous wire

Iac

M

%400~R

)MHz 1(~Z

DC

CoFeSiB

frequencyfrequency

external fieldexternal field

Enhanced skin effect in magnetic wire

GMI spec.

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GMI specifications

Commercial: ~100 $

MR

State variable Z @ MHz

B-field Vector

Bnoise @ 1 Hz

sources

~3 nT/Hz1/f mag noiseTemp fluct. M

JohnsonPerming

- Volume 0.01 mm3 (wire)

Operating T RT

Power Batter

27“Thin Film Magneto-resistive SensorsS. Tumanski, IOP (2001).

Magneto-resistive (MR) sensors AMR - Anisotropic MR

Single ferromagnetic film NiFe

2% change in resistance

Spintronic: GMR trilayer w/NM spacer

60% R/Rmin Co/Cu/Co

“Spin Valve”

TMR – Insulator spacer 472% R/Rmin at R.T.

CoFeB/MgO/CoFeB

Hayakawa, APL (2006)

IM

FM

NM

FM

**

*

*Forensics

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MR Sensors – spatial resolution

256 element AMR linear array

Thermally balanced bridges

High speed magnetic tape

imaging – forensics, archival

NDE imaging

Cassette Tape – forensic analysis4 mm

45 mm

erase headstop event

write headstop event

da Silva, et al., subm. RSI (2007)

Current flow in VLSI RAM w/short

2 cm -Iy

+Ix

-Ix

+Iy

4 mm

V+V-

I-I-

16 m x 256

I+

BARC.

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MR biomolecular recognition1. Nano-scale magnetic labels that attach to target

2. GMR arrays with probe

3. Probes attach to targets

Need very sensitive magnetic detector arrays

Goal: high accuracy chemical assays

Device Applications Using SDT, Tondra et. alSpringer Lecture Notes in Physics, V593, 278-289 (2002)

“BARC”BeadArray Counter

MR sens.

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MR as low field sensors AMR

Large area films

GMRSmall sensors

Commercial: ~ $

2 Unshielded sensors

2 shielded

Fluxconcentrators

TMR

“Low frequency picotesla field detection…”Chavez, et. al, APL 91, 102504 (2007).F.C.

State variable Resistance

B-field Vector

Bnoise @ 1 Hz

sources

~200 pT/Hz1/f mag noiseTemp fluct. MJohnson/Shot

Perming

- Volume 0.001 mm3 film

Operating T RT

Power battery

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The joy of flux concentrators

Bext a

Need:

Soft ferromagnet

High M = No hysterisis Gain up to ~50 No increase in noise Increase in form factor

2 cm

Noise

TMR with F.C.

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Spectral noise measurements

Hall FC

10-1 100 101 102 103 10410-13

10-12

10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

TMR-FC

TMR

GMRGMI

Hall

Fluxgate

AMR

Noi

se f

loor

(T

/Hz1/

2 )

Frequency (Hz)

without fluxconcentrator

with external flux concentrator

Stutzke, Russek, Pappas, and Tondra, J. Appl. Phys. 97, 10Q107 (2005)Yuan, Halloran, da Silva, Pappas, J. Appl. Phys. submitted (2007)

1 p

1 n

1

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Integrated Hall sensors with flux concentrators

“Bridging the gap between AMR, GMR and Hall Magnetic sensorsPopovic, et. al, PROC. 23rd MIEL, V1, NIŠ, YUGOSLAVIA, 12-15 MAY, 2002Hall spec.

Noise @ 1Hz

(nT/Hz)

White noise (> 100 Hz)

(nT/Hz)

BICMOS Hall no flux concentrator 300 200

CMOS - internal flux concentrators 300 30

CMOS - both internal and

external flux concentrators

30 3

Internal fluxconcentrators

Hall element

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V

I

Hall Effect specificationsState variable Voltage

B-field Vector

Bnoise @ 1 Hz 300 nT/Hz

30 nT/Hz w/FC’s

- Volume 0.001 mm3

Operating T RT

Power battery

Commercial: ~$ 0.1 1

Applications

Keyboard switches

Brushless DC motors

Tachometers

Flowmeters

InAs thin film

Disruptive - hybrid

B

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Disruptive technologies?Superconducting flux concentrator

State variable GMR voltage

B-field Vector

Bnoise @ 1 Hz 32 fT/Hz

- Volume 0.1 cm3

Operating T cryogenic

Power line

Field GainYBCO ~ 100Nb ~ 500

Hybrid S.C./GMR

“…An Alternative to SQUIDs”Pannetier, et. al, IEEE Trans SuperCond 15(2), 892 (2005)ME

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Magneto-electric

DisruptiveNo power required

Two terminal deviceHigh impedance output

State variable Piezo voltage

B-field Vector

Bnoise @ 1 Hz

sources

1 nT/Hz

pyro/static

- Volume 1 mm3

Operating T -40 to 150C

Power 0

Dong, et. al APL V86, 102901 (2005).Hristoforou, Sensors and Actuators A132 (2006) .

Magnetostrictive+

piezo-electricmultilayer

Terfenol-D

H

PMN-PT

VME

MO

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Magneto-optic

State variable Light intensity

B-field Vector

Bnoise @ 1 Hz 1.4 pT/Hz

- Volume 1 cm3

Operating T ambient

Power line

Mirror-coated iron garnet

Magnetometer head

Ferrite Flux Concentrators

• Light polarization changes in garnet

• Rotation B-field (Faraday effect)

• Sensed with interferometer

Fiber-optic

Deeter, et. al Electronics Letters, V29(11), p 993 (1993).

Youber, Pinassaud, Sensors and Actuators A129, 126 (2006).

Disruptive• Light not affected by B

• Remote sensors• High speed• Imaging capability (light)

• NDE

Spintronic

B

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More spintronic sensors… Extraordinary MR (EMR)

Hall effect with metal impurity Based on 106 MR in van der Pauw disks

Non-magnetic materials Mesoscopic devices R/R ~ 35% in field

Replacement for GMR in hdds? 220% TMR in 2004 …

Au

InSb

BSemiconductor

Au impurity

“Magnetic Field Nanosensors, Solin, Scientific American V291, 71 (2004)

VI

CMR

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Colossal Magneto-resistance Manganite materials

La1-xMxMnO3

Phase transition – Jahn-Teller distortion Low T – Ferromagnetic High T – Paramagnetic semiconductor

Large B-dependent resistance change at critical temperature (~260 K)

Uses at room temperature: Contact-less potentiometers Bolometers

Barriers to commercialization High fields Single crystal materials High growth temperatures

Haghiri-Gosnet, Renard, J. Phys. D: Appl. Phys. 36 (2003) R127–R150Transistors

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Spin transistors Tunnel junction based devices

van Dijken, et. al, APL V83(5) 951 (2003)

Spin dependent hot e- transmission CuTunnel BarrierSpin ValveSchottky barrier

3400% magneto-conductance at 77 K

Relatively low currents (10 A), a lot of noise sources

Spin-FET Quantum wire channel between

2 half metal contacts

Many devices in parallel (1011)

can give ~fT/Hz noise level

Wan, Cahay, Bandyopadhyay, JAP 102, 034301 (2007) Compilation

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Sensor B Bn (pT/Hz @ 1 Hz) Volume Power

SQUID v .01 1 cm3 Line

Proton s 1 1 cm3 battery

e- He4/CSAM/SERF s/s/v 1 / 5 / .001 mm3 – cm3 Battery-line

Fluxgate v 10 1 cm3 battery

GMI v 3000 0.01 mm3 battery

MR v 200 0.001 mm3 battery

Hybrid GMR/SC

v .032 .1 cm3 line

Hall v 30,000 0.001 mm3 battery

ME v 1000 1 mm3 0

Magneto-optic v 1 cm3 line

Compilation

Trend: Noise decreases as Volume increases

Bn vs. V

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1.0E-06

1.0E-04

1.0E-02

1.0E+00

1.0E+02

1.0E+04

1.0E-07 1.0E-05 1.0E-03 1.0E-01 1.0E+01

Volume (cm^3)

No

ise

(pT

/rtH

z)Bnoise vs. Volume

SERF

He4

SQUID

ProtonF.GMO

Hybrid

CSAM

MEGMIHall

MR

Magn. Sensors

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Noise vs. volume in magnetic sensors Fluxgate magnetometers

Increase volume () & decrease loss ()

AMR – make up for low R/R by: Large arrays of elements (volume)

good magnetic properties (reduce

Flux concentrators Increase volume

Softer, low hysterisis to reduce

''TB mag,n

E resolution

“Fundamental limits of fluxgate magnetometers…” Koch et al, APL V75, 3862 (1999)

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Compare sensors based on volumetric energy resolution

Energy resolution Noise Power Volume

D. Robbes / Sensors and Actuators A 129 (2006) 86–93

0

2n

2

Be

Conclusions

S.C. F.M

DeviceEnergy Resolution

e(J/Hz)

SQUID w/pickup 1 x 10-30

SERF 3 x 10-29

Hybrid GMR/SC 4 x 10-29

GMI 6 x 10-28

AMR 7 x 10-26

CSAM 2 x 10-25

He4 4 x 10-24

Fluxgate 3 x 10-23

GMR w/feedback 4 x 10-23

Hall 5 x 10-23

Magnetoelectric 5 x 10-23

TMR w/FC 1 x 10-19

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Conclusions High sensitivity magnetometers research very active Many advances to be made in conventional devices

Potentially disruptive technologies Move to smaller, lower power, nano-fabrication

Noise floor decreases with volume Can look at intrinsic energy resolution of sensor Also need to evaluate high sensitivity against many

other parameters: Spatial resolution bandwidth dynamic range cost, …

Acknowledgement.

Pick the right tool for the job!

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Acknowledgements

Steve Russek

Bill Egelhoff

John Unguris

Mike Donahue

John Kitching

Fabio da Silva

Sean Halloran

Lu Yuan

Jeff Kline