High Sensitivity Magnetic Field Sensor Technology

David P. Pappas

National Institute of Standards & Technology

Boulder, CO

Market Analysis - Worldwide

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

NDT $0.1M

Applications

Health Care

Geophysical

Astronomical

Archeology

Non-destructive

testing

Data storage

North Caroline Department of Cultural Resources“Queen Anne’s Revenge” shipwreck site Beufort, NC

Mars Global Explorer (1998)

Magnetic RAM

Field Ranges & Frequencies

F.L. FagalyMagnetics Business & TechnologySummer 2002

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

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

1 fT

1 100 10,0000.010.0001Frequency (Hz)

Mag

netic

fiel

d R

ange

1 pT

Geophysical Industrial/NDE

MagneticAnomaly

Magneto-cardiography

Magneto-encephalography

1 nT

Magnetic fields… Induce currents in conductors

Change magnetic properties matter

Affect electronic properties of materials

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

Magnetometer technologies Induction

Search Coil

Ferromagnetic Fluxgate Magneto-Resistive, Impedance, Optical, Electric…

Semiconducting Hall Effect, spintronics

Superconducting SQUIDS – DC,RF / Low TC, High TC

Spin Resonance Proton, electron

Important properties State variable

B Measurement – Vector or scalar?

Noise (@ 1 Hz)

Operating Temp.

Power

Form Factor

Commercially available?

State measurement Low noise excitation source -

Voltage, current, light, …

Sense state with detector

Flux feedback is typical Linearize

Dynamic Range ~ 22 bits

Limits bandwidth & slew rate

Complicated

Bext

Bf

B

M

Noise metrology Shielded container/room Low noise preamplifiers Spectrum analyzer

A-B Cross-correlation reducesamplifier noise

StateMeasurement

A B

Stutzke, Russek, Pappas, and Tondra, J. Appl. Phys. 97, 10Q107 (2005)

Billingsley (2007)

SQUID Magnetometer

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

State variable Voltage (100’s

V)

B-field Vector

Noise @ 1 Hz

sources

5 fT/HzJohnson

Flux trapping

Operating T cryogenic

Power Line

Form Factor m3

2nd DerivativePickup coil

Commercial: 10 – 100’s k$

Noise Spectral distribution Normalized for 1 Hz bandwidth Noise integrates for wider bandwidth

fT/Hz

Hz

SyntheticGradiometer

Unprocessed

10 fT/Hz

Low TC SQUID array

Penne, et al., PHILOSOPHICAL MAGAZINE B, 2000, VOL. 80, NO. 5, 937± 948

1 pT/Hz

1 10 100 1000

1pT/Hz

e.g. magneto-cardiography

Oh, et. al JKPS (2007)

Low TC SQUID – 10 fT/Hz @ 1 Hz High TC SQUID – 1pT/Hz @ 1 Hz

.01 0.1 1 10 100

Harold Weinstock

“Don’t use a SQUID when a

simpler technology is available”

Resonance magnetometers Nuclear spin resonance

Protons water, methanol, kerosene

He3

Molecules - Tempone

Electron spin resonance He4

Alkali metals – Na, K, Rb

Bext

Proton magnetometerState variable Frequency

B-field Scalar

Noise @ 1 Hz

sources

~10 PT/Hz

depolarization

Operating T -20 => 50 oC

Power Battery

Form Factor cm3

Commercial: 5 k$

mT 0.05 ~ B

MHz/T 42~

kHz 2

2/B f

Earth

otonPr

EarthotonPr

Electron spin magnetometerState variable Frequency

Vapor cell

Photodetector

B

RFCoils

/4 Filter

Laser

• Noble gas – He4

• e = 28 GHz/T => f ~ 1 MHz

• Spin-exchange relaxation free (SERF)

• K metal vapor

• Low field, high density gas

• Optimized for high sensitivity

• Chip scale atomic magnetometer (CSAM)

• Rb metal vapor

• Optimized for low power

• Very small form factor

• Can also implement SERF

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

e--spin magnetometer - He4

Scalar B-field 1 pT/Hz Cell not heated Low power

~ 10’s cm3

JPL SAC-C missionNov. (2000)

e--spin magnetometer Spin-exchange relaxation free

Vector B-field <1 f T/Hz cell ~ 180 oC Line power

~ m3

e--spin magnetometer Chip Scale Atomic magnetometer

Scalar B-field 5 pT/Hz Cell 110 oC Very low power

~20 mm3

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

Ferromagnetic magnetometers

Fluxgate

Magneto-resistive AMR – Anisotropic MR

GMR – Giant MR

TMR – Tunneling MR

Giant Magneto-impedance

Magneto-striction

Fluxgate

M

H

Bext

Bext

Hmod(f)

MState variable Inductive 2f

B-field Vector

Noise @ 1 Hz

sources

~5 pT/Hz

MagneticJohnsonPerming

Operating T RT, 30

ppm/oC

Power Battery

Form Factor ~20 mm core

“Magnetic Sensors and Magnetometers” P. Ripka, Artech, 2001Commercial: ~1 k$

Pickup(2f)Drive(f)

Advances in Fluxgate technology

Apply current in core

Single domain rotation

100 f T/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)

Magneto-resistive (MR) sensors

AMR - Anisotropic MR Single ferromagnetic film

2% change in resistance

GMR – Cu spacer Up to 60% change

TMR – Insulator spacer Insulator => 400% change

IMFM

FM

NM

FM

**

*

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

Specs: MR sensors State variable Resistance

B-field Vector

Noise @ 1 Hz

sources

~100 pT/Hz1/f mag noiseTemp fluct. MJohnson/Shot

Perming

Operating T RT, 60 ppm/oC

Power Low

Form Factor m2

AMRHoneywell

Philips

GMRNVE

Commercial: ~ $

Fluxguides

2 Unshielded sensors

2 shielded

TMR

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

The joy of flux guides:

Bext

M

For small gap:Bg ~ 10 Bext

Bext

Bint~10Bext Bg~Bint

Bound Current

“soft” ferromagnet

Advanced flux guidesBext

a

b

Bext

M Need:

Soft ferromagnet

High M = No hysterisis

=> Gain up to ~50

“a” concentrated“b” shielded

Disruptive technologies?Hybrid superconductor/GMR

State variable GMR

B-field Vector

Noise @ <1 Hz 32 fT/Hz

Operating T cryogenic

Power low

Form Factor Loop ~ 3x3 mmField GainYBCO ~ 100Nb ~ 500

Superconductingflux concentrator

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

MR sensors - high spatial resolutionHigh Frequency Data storage

HDD read head 100 Gb/in2

0.2 m wide, 1 GHz BW

~ 100 pT/Hz from SNRMgO MTJ

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

10 pT/Hz

MR Sensors – scalability & imaging 256 element AMR linear array

Thermally balanced bridges

Image magnetic tapes real

time – forensics, archival

NDE imaging I+

Cassette Tape – forensic analysisFerrofluid image

V+V-

I-I-

16 m

MR biomolecular recognition MR arrays with probe DNA

Magnetic labels that attach to target DNA

Labels => Probes, read out MR

Device Applications Using Spin Dependent Tunneling and Nanostructured Materials M. Tondra, D. Wang, Z. Qian, Springer Lecture Notes in Physics, V593, 278-289 (2002)

“BARC”BeadArray Counter

Magneto-electric

Disruptive technology?No power required

Two terminal deviceHigh impedance output

State variable Piezo voltage

B-field Vector

Noise @ <1 Hz

sources

1 nT/Hzpyro/static

Operating T -40 to 150C

Power 0

Form Factor 10’s mm3

Dong, Zhai, Xin, Li, ViehlandAPL V86, 102901 (2005)

Magnetostrictive+

piezo-electricmultilayer

Terfenol-D

H

Giant Magneto-impedance

“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 H

MState variable Z @ ~ 1 MHz

B-field Vector

Noise @ 1 Hz

sources

~100 pT/Hz1/f mag noiseTemp fluct. M

JohnsonPerming

Operating T RT

Power Very low

Form Factor mm2

frequencyfrequency

external fieldexternal field

%400~R

Z

DC

Commercial: ~100 $

CoFeSiB

Tried and True - Hall EffectState variable Voltage

B-field Vector

Noise @ 1 Hz

sources

~100 pT/Hze- mobility

Offsets1/f noise

Operating T RT

Power Very low

Form Factor 0.1 mm2 - Si

Commercial: ~0.1 $

Spin Transistors

Magneto-optic

Search Coils

Acknowledgements

Steve Russek

Bill Egelhoff

John Unguris

Mike Donahue

John Kitching

Fabio da Silva

Sean Halloran

Lu Yuan

Comparison of MR & Fluxgates

10-1 100 101 102 103 10410-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

NVE AAH002NIST MTJ

Aichi GMI

Allegro Si Hall

coil 2.5 cm x 5 cm

Fluxgate

HW AMR

NVE SDT

NVE GMR

HW AMR

NVE GMR

Min

mum

Det

ecta

ble

Fiel

d (T

/Hz

1/2 )

Frequency (Hz)

G111J