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High Sensitivity Magnetic Field Sensor Technology overview. David P. Pappas National Institute of Standards & Technology Boulder, CO. Outline. High sensitivity applications & signal measurements Description of various types of sensors used New technologies

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High Sensitivity Magnetic Field Sensor Technology overview

David P. Pappas

National Institute of Standards & Technology

Boulder, CO


Outline

  • High sensitivity applications & signal measurements

  • Description of various types of sensors used

  • New technologies

  • Comparison of sensor metrics


Market analysis - magnetic sensors

  • 2005 Revenue Worldwide - $947M

  • Growth rate 9.4%

Application

Type

“World Magnetic Sensor Components and Modules/Sub-systems Markets”

Frost & Sullivan, (2005)


Mars Global Surveyor

Magnetic anomalies

Blackbeard’s last stand

2003 Halloween magnetic storm

Magneto-encephalography

Magneto-

Cardiography

  • 120 observatories world-wide

  • Fluxgates

  • Proton magnetometers

  • Earth interior dynamics

  • Mineral exploration

  • GPS stability

  • Satellite electronics

  • Increased radiation

Mars Global Explorer (1998)

North Caroline Department of Cultural Resources

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

“Magnetic Monitoring of Earth and Space

Jeff Love, USGS

Physics Today Feb. 2008

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

Applications

  • Geophysical

  • Astronomical

  • Archeology

  • Health Care

  • Data storage

SI units


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

A

B-field tesla (T)

kg/(As2)

e.g. 1 A @ 1 m:

F = BA

SI - Le Système International d’Unitès

  • What do we measure?

B = flux density

= “Magnetic induction” field

= mH includes medium

r (m)

I (A)

Use m0 = permeability of free space

= 4p x 10-6 Wb/Am

B = 210-7 T

Frequency


B-field Ranges & Frequencies

1 mT (10-3)

1 gauss  10-4 T ~ Earth’s B-field

Industrial

1 mT (10-6)

1 A @ 1 m

Industrial

1 nT

Geophysical

Geophysical

Magneto-

cardiography

Non-destructive

evaluation

& hdd’s

1 nT (10-9)

Magnetic field Range

B-field

Magnetic

Anomaly

Magneto-cardiography

1 pT

Magnetic

Anomaly

1 pT (10-12)

Magneto-

encephalography

Magneto-

encephalography

1 fT (10-15)

1 fT

1 aT (10-18)

1

1

100

100

10,000

10,000

0.0001

0.01

0.01

0.0001

Frequency (Hz)

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

Technologies


B

B-field effects

  • Induction (Faraday’s Law)

    • Search Coil

    • Fluxgate

    • Giant magneto-impedance ( + skin effect)

  • Torque -

    • Magnetic resonance (optical pumping)

      • Proton – f ~ 4 kHz/gauss

      • Electron – f ~ 3 MHz/gauss

    • Magneto-striction

  • Scattering

    • Magneto-resistance (AMR)

    • Spintronics

      • Giant MR, Tunneling MR, Spin Xtor…

    • Hall Effect (Lorentz force)

    • Magneto-optical

  • Wave function interference

    • Superconducting Quantum Interference Device (SQUID)

*

*

FM

*

NM

FM

State


Bext

Bf

State measurement

V

  • Low noise excitation source -

    • Voltage, current, light, …

  • Detector volume -  = Ah

  • Sense state

    • e.g. sensitivity = V/T

  • Flux feedback is typical

    • Linearize

    • Dynamic Range

    • Complicated

    • Limits slew rate & bandwidth

A

h

S

B

Noise


Units

1/f

White

State

Measurement

Noise metrology

  • Low noise preamplifiers

  • Magnetically shielded container

    (or room)

  • Spectrum analyzer

    • Noise power vs. frequency = V2/Hz

    • field noise = power / sensitivity

100

SQUID

magnetometer

(w/gradiometer)

10

1

pT/Hz

0.1

.01

0.001

0.01 0.1 1 10 100

Hz

Preamp


extra noise

100

10

1pT/Hz

1

pT/Hz

~60 pT

0.1

.01

0.001

=> Use noise at lowest frequency in bandwidth as benchmark

e.g. Magneto-cardiography

Magnetometer 2

Magnetometer 1

.01 0.1 1 10 100

1 10 100 1000

frequency


Benchmark properties:

SQUID


Superconducting Quantum Interference Devices

Signal (V)

I

Superconductor

B

IR

IL

B(T)

Tunnel

Junctions

Left-Right phase shifted by B

PU loop


Pickup loops for SQUIDS

  • One loop: measure BZ

  • Two opposing loops:

    • dBZ/dz (1st order gradiometer)

    • Good noise rejection

  • Opposing gradiometers:

    • dBZ2/dz2 (2nd order gradiometer)

    • High noise rejection

  • Universal magnetometer configurations

N

S

Z

SQUID specs


SQUID Magnetometer

Integrated

Systems

Discrete

components

Commercial: 10 – 100’s k$

“The SQUID Handbook,”

Clarke & Braginski, Wiley-VCH 2004

MRI


SQUID detected Magnetic Resonance Image

B

  • Low polarizing B-field

    • 60 mT

  • Low precession field

    • 132 mT

  • Low resonance f

    • ~ 6 kHz

  • Don’t need superconducting magnets

Image of human forearm

Clarke, et. al, ANRV 317-BE09-02 (2007)


Resonance magnetometers

f  Bext

  • Proton Nuclear spin resonance

    • f = 43 MHz/T

      • Water, methanol, kerosene

      • Overhauser effect

        • Transfer e- spin to protons

        • He3, Tempone

Bext

Proton


Proton magnetometer

  • Kerosene cell

  • Toroidal excitation

  • & pickup

Commercial: 5 k$

Olsen, et. al (1976)

From Ripka, (2001)

e- spin


Bext

Resonance magnetometers (2)

f  Bext

  • Electron spin resonance

    • f = 28 GHz/T

    • He4: 23S1 - optical pumping

    • Alkali metals (Na, K, Rb)

Photodetector

Vapor cell

RF

Coils

l/4 Filter

Laser

Proton


He4 e--spin magnetometer

Smith, et al (1991)

from Ripka (2001)

JPL - SAC-C mission

Nov. (2000)

CSAM


e--spin magnetometer Spin-exchange relaxation free

  • K metal vapor

  • Low field, high density of atoms

  • Line narrowing effect

  • All-optical excitation & pickup

  • =>Optimized for high sensitivity

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

Solid state


Solid state magnetometers

  • Semi-conductors

    • Hall effect

  • Ferromagnetic based:

    • Magneto-resistive

    • AMR – Anisotropic MR

    • Spintronic

      • GMR – Giant MR, TMR – Tunneling M

    • Fluxgate

    • Giant magneto-impedance

  • Disruptive technologies

    • Hybrid superconductor/solid state

    • Colossal magneto-resistance

    • Magneto-electric

    • Spin Transistors

Hall


B

Hall Effect

V

I

  • In-line with CMOS

  • Applications

    • Keyboard switches

    • Brushless DC motors

    • Tachometers

    • Flowmeters

    • etc.

Commercial: ~$ 0.1  1

Fruounchi, Demiere, Radjelovic, Popovic, ISSC (2001)

noise


Spectral noise measurements

1 m

Hall

)

1/2

1 n

GMI

GMR

AMR

Noise floor (T/Hz

TMR

1 p

Fluxgate

-13

-1

0

1

2

3

4

10

10

10

10

10

10

Frequency (Hz)

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

Yuan, Halloran, da Silva, Pappas, J. Appl. Phys. submitted (2007)

MR


*

*

*

*

“Thin Film Magneto-resistive Sensors

S. Tumanski, IOP (2001).

Magneto-resistive (MR) sensors

I

  • AMR - Anisotropic MR

    • Single ferromagnetic film NiFe

    • 2% change in resistance

  • Spintronic:

    • GMR trilayer w/NM spacer

      • 60% DR/Rmin Co/Cu/Co

      • “Spin Valve”

    • TMR – Insulator spacer

      • 500% DR/Rmin at R.T.

      • CoFeB/MgO/CoFeB

      • Hayakawa, APL (2006)

M

FM

NM

FM

Low field


Flux

concentrators

MR as low field sensors

AMR

Large area films

2 Unshielded sensors

GMR

Small

sensors

2 shielded

TMR

Commercial: ~ 1$

“Low frequency picotesla field detection…”

Chavez, et. al, APL 91, 102504 (2007).

F.C.


Application of flux concentrators

Bext

a

  • Need:

  • Soft ferromagnet

  • High M = cH

  • No hysterisis

  • Gain up to ~50

  • No increase in noise

  • Increase in volume

TMR with F.C.

2 cm

Noise


with external

flux concentrator

Spectral noise measurements

1 m

without flux

concentrator

1 n

1 p

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

Yuan, Halloran, da Silva, Pappas, J. Appl. Phys. submitted (2007)

fluxgate


Bext

Fluxgate

Drive(f)

Pickup(2f)

Bext

M

M

H

Hmod(f)

Commercial: ~1 k$

“Magnetic Sensors and

Magnetometers” P. Ripka, Artech, 2001

GMI


Magnetic amorphous wire

Enhanced skin effect in magnetic wire

frequency

external field

Giant Magneto-impedance (GMI)

Iac

CoFeSiB

M

“Giant magneto-impedance and its applications”

Tannous C., Gieraltowski, Jour Mat. Sci: Mater. in

Electronics, V15(3) pp 125-133 (2004)

GMI spec.


GMI specifications

Commercial: ~100 $

Disruptive


Disruptive technologies?Superconducting flux concentrator

Hybrid S.C./GMR

Field Gain

Nb ~ 500

YBCO ~2000

Sensor

“…An Alternative to SQUIDs”

Pannetier, et. al, IEEE Trans SuperCond 15(2), 892 (2005)

Colossal


Colossal Magneto-resistance

  • Manganite materials

    • La1-xMxMnO3

    • Phase transition – Jahn-Teller distortion

      • Low T – Ferromagnetic

      • High T – Paramagnetic semiconductor

  • ~ 500% change of resistance

  • Barriers to commercialization

    • Optimal DR/R at ~260 K

    • High fields

    • Single crystal materials

    • High growth temperatures

  • Can integrate with superconducting flux concentrators

Haghiri-Gosnet, Renard, J. Phys. D: Appl. Phys. 36 (2003) R127–R150

ME


Magneto-electric

Magnetostrictive

+

piezo-electric

multilayer

H

PMN-PT

VME

Terfenol-D

Disruptive

No power required

Two terminal device

High impedance output

Zhai, Li, Viehland, Bichuin, JAP (2007)

Dong, et. al APL V86, 102901 (2005).

EMR


Extraordinary MR (EMR)

B

Semiconductor

  • Hall effect with metal impurity

    • Based on 106 MR in van der Pauw disks

  • Non-magnetic materials

  • Mesoscopic devices

  • DR/R ~ 35% in field

  • Replacement for GMR in hdds?

    • Can’t compete with TMR in MgO

    • May scale better at small sizes

  • Au impurity

    Au

    V

    I

    InSb

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

    Compilation


    Compilation

    Trend: Noise increases as Volume decreases

    Bn vs. V


    Bnoise vs. Volume

    Hall

    1.0E+04

    GMI

    ME

    MR

    1.0E+02

    Proton

    CSAM

    F.G

    He4

    MO

    1.0E+00

    Noise (pT/rtHz)

    Hybrid

    1.0E-02

    SQUID

    SERF

    1.0E-04

    1.0E-06

    1.0E-07

    1.0E-05

    1.0E-03

    1.0E-01

    1.0E+01

    Volume (cm^3)

    Volumetric energy


    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, …

    Pick the right tool for the job!

    Acknowledgement.


    Acknowledgements

    • Steve Russek

    • Bill Egelhoff

    • John Unguris

    • Mike Donahue

    • John Kitching

    • Fabio da Silva

    • Sean Halloran

    • Lu Yuan

    • Jeff Kline


    Noise vs. volume in magnetic sensors

    • Fluxgate magnetometers

      • Increase volume () & decrease loss ()

    • AMR – make up for low DR/R by:

      • Large arrays of elements (volume)

      • good magnetic properties (reduce )

    • Flux concentrators

      • Increase volume

      • Softer, low hysterisis to reduce 

    “Fundamental limits of fluxgate magnetometers…”

    Koch et al, APL V75, 3862 (1999)

    E resolution


    I+

    I-

    I-

    V+

    V-

    16 mm x 256

    Current flow in

    VLSI RAM w/short

    4 mm

    +Ix

    Cassette Tape – forensic analysis

    write head

    stop event

    erase head

    stop event

    +Iy

    2 cm

    -Iy

    -Ix

    45 mm

    MR Sensors – spatial resolution

    • 256 element AMR linear array

    • Thermally balanced bridges

    • High speed magnetic tape imaging – forensics, archival

    • NDE imaging

    4 mm

    BARC.

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


    Innovations in Fluxgate technology

    Micro-fluxgates

    Circumferential Magnetization

    • Planar fabrication

    • 80 pT/Hz @ 1 Hz

    • Apply current in core

    • Single domain rotation

    • 1 pT/Hz @ 1 Hz

    I

    M

    Koch, Rosen, APL 78(13) 1897 (2001)

    Kawahito S., IEEE J. Solid State

    Circuits 34(12), 1843 (1999)

    GMI


    e--spin magnetometer Chip scale atomic magnetometer

    • Rb metal vapor

    • Optimized for low power

    • Very small form factor

    4.5 mm

    P. D. D. Schwindt, et al.

    APL 90, 081102 (2007).

    SERF


    Magneto-optic

    Magnetometer head

    Mirror-coated iron garnet

    B

    Fiber-

    optic

    Ferrite Flux Concentrators

    • Light polarization changes in garnet

    • Rotation  B-field (Faraday effect)

    • Sensed with interferometer

    • Disruptive

    • Light not affected by B

      • Remote sensors

    • High speed

    • Imaging capability (light)

      • NDE

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

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

    Spintronic


    Spin transistors

    • Tunnel junction based devices

      Spin dependent hot e- transmission

      • CuTunnel BarrierSpin ValveSchottky barrier

    • 3400% magneto-conductance at 77 K

    • Relatively low currents (10 mA)

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

    Compilation


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