1 high sensitivity magnetic field sensor technology overview david p. pappas national institute of...
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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
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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