High Sensitivity Magnetic Field Sensor Technology overview David

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

Market analysis - magnetic sensors n 2005 Revenue Worldwide - $947 M n Growth rate 9. 4% Application 2 Type “World Magnetic Sensor Components and Modules/Sub-systems Markets” Frost & Sullivan, (2005)

Outline 3 n High sensitivity applications n Noise & signal measurement n Description of various types of sensors n Addition of flux concentrators n Summary

Applications Bio-magnetic tag detection Magneto. Cardiography n Health Care n Geophysical n Astronomical n Archeology n Non-destructive evaluation (NDE) n 4 SI units Magneto-encephalography Magnetic RAM Data storage Mars Global Explorer (1998) North Caroline Department of Cultural Resources “Queen Anne’s Revenge” shipwreck site Beufort, NC Frietas, ferreira, JPL -Cardoso, SAC-C Cardoso mission “Biomagnetism using SQUIDs: Status and Perspectives” J. Phys. : Condens. Mater 19, 165221 (2007) Nov. (2000) Sternickel, Braginski, Supercond. Sci. Technol. 19 S 160–S 171 (2006).

SI - Le Système International d’Unitès “Magnetic field intensity”: H-field A/m • What do we measure? r (m) I (A) B = flux density = “Magnetic induction” field Use m 0 = permeability of free space A B = m 0 H B-field tesla (T) F = B A 5 Frequency e. g. 1 A @ 1 m kg/(As 2) H = ~0. 1 A/m B = 2 10 -7 T

B-field Ranges & Frequencies B-field Magnetic field Range 1 m. T 1 n. T� 1 gauss 10 -4 T ~ Earth’s B-field 1 A@1 m Geophysical 1 n. T 1 p. T Industrial/NDE Magnetocardiography Magneto-cardiography Magnetic Anomaly Magnetoencephalography 11 f. T 0. 0001 6 effects Industrial 0. 01 11 100 Frequency(Hz) 10, 000 F. L. Fagaly Magnetics Business & Technology Summer 2002 Adapted from “Magnetic Sensors and Magnetometers”, P. Ripka, Artech, (2001)

B-fields… n Induce voltages n Affect scattering of electrons in matter n Change phase of currents flowing in superconductors n Create energy level splittings in atoms => Use these effects to build a toolbox for field detection in important applications 7 Technologies

Magnetometer technologies n Induction q q q n Scattering q q n SQUIDS Spin Resonance q 8 State Anisotropic magneto-resistive (AMR) Spintronic – Giant MR, Tunneling MR, Spin transistor Hall Effect Magneto-optical Superconducting q n Search Coil Fluxgate Giant magneto-impedance Proton, electron

State measurement n Low noise excitation source q Voltage, current, light, … n Sense state with detector n Flux feedback is typical þ Linearize þ Dynamic Range ýComplicated ýLimits slew rate & bandwidth 9 Noise Bext S Bf S B

Noise metrology n Magnetically shielded container (or room) n Low noise preamplifiers n Spectrum analyzer – P = V 2/Hz q field noise = power / sensitivity Units: 1/f 10, 000 f T/ Hz 1, 000 State Measurement 100 White 10 1 0. 01 10 Benchmarks Low TCSQUID magnetometer (w/gradiometer) 100, 000 Preamp 0. 1 1 Hz 10 100

Benchmark properties: State variable B-field measurement Noise @ 1 Hz Operating T V, f, etc Vector/scalar T/ Hz Cryogenic/RT Volume of sense element Power – form factor 11 SQUID Line/Battery

Superconducting Quantum Interference Devices I IL B IR Tunnel Junctions Left-Right phase shifted by B 12 PU loop Signal B

Pickup loops for SQUIDS n One loop: measure BZ n Two opposing loops: N Z 13 SQUID specs n S q d. BZ/dz (1 st order gradiometer) q Good noise rejection Opposing gradiometers: q d. BZ 2/dz 2 (2 nd order gradiometer) q High noise rejection

SQUID Magnetometer State variable Voltage (10’s m. V) B-field Vector, gradients Noise @ 1 Hz ~10 f. T/ Hz Low TC Operating T Volume Power Integrated Systems Discrete components cryogenic ~ 1 cm 3 coil Line Commercial: 10 – 100’s k$ 14 Resonance “The SQUID Handbook, ” Clarke & Braginski, Wiley-VCH 2004

Real time magneto-cardiography with SQUID magnetometer Oh, et. al JKPS (2007) ~60 p. T 15 Benchmark

Resonance magnetometers f Bext n Nuclear spin resonance q Protons n water, methanol, kerosene n Overhauser effect: q n Electron spin resonance q 16 Proton He 3, Tempone He 4, Alkali metals (Na, K, Rb) Bext

Proton magnetometer State variable Frequency ~ k. Hz B-field Scalar Noise @ 1 Hz ~10 p. T/ Hz sources depolarization Operating T Volume Power -20 => 50 o. C • Kerosene cell • Toroidal excitation & pickup 1 cm 3 cell Battery Commercial: 5 k$ 17 e spin Olsen, et. al (1976) From Ripka, (2001)

Electron spin magnetometers Photodetector RF Coils Vapor cell Bext l/4 Filter Laser 18 He 4 Budker, Romalis, Nature Physics, 3(4), 227 -234 (2007)

He 4 e--spin magnetometer State variable Frequency ~ MHz B-field vector/scalar Noise @ 1 Hz 1 p. T/ Hz Operating T ambient Volume Power 19 CSAM ~10 cm 3 cell battery JPL - SAC-C mission Nov. (2000) Smith, et al (1991) from Ripka (2001)

e--spin magnetometer Chip scale atomic magnetometer State variable B-field Scalar Noise @ 1 Hz 5 p. T/ Hz Operating T Volume Power 20 SERF Rb metal vapor Optimized for low power Very small form factor Frequency 110 o. C 20 mm 3 4. 5 mm Small battery P. D. D. Schwindt, et al. APL 90, 081102 (2007).

e--spin magnetometer Spin-exchange relaxation free State variable Frequency B-field Vector < 100 n. T Noise @ 1 Hz < 1 f. T/ Hz Operating T 180 o. C Volume ~ 3 cm 3 Power 21 Solid state K metal vapor Low field, high density of atoms Line narrowing effect All-optical excitation & pickup =>Optimized for high sensitivity line Kominis, et. al, Nature 422, 596 (2003)

Solid state magnetometers n n Inductive q Fluxgate q Giant magneto-impedance Magneto-resistive q n n 22 AMR – Anisotropic MR Spintronic q GMR – Giant MR q TMR – Tunneling MR Disruptive technologies q Hybrid superconductor/solid state q Magneto-striction

Fluxgate State variable Drive(f) Bext Inductive 2 f B-field Vector Noise @ 1 Hz <10 p. T/ Hz sources Magnetic Johnson Perming Operating T Volume Power Pickup(2 f) M M H Bext Hmod(f) RT 1 cm 3 battery Commercial: ~1 k$ 23 FG innov. “Magnetic Sensors and Magnetometers” P. Ripka, Artech, 2001

Innovations in Fluxgate technology Micro-fluxgates Circumferential Magnetization n Apply current in core M I n Single domain rotation n 100 f. T/ Hz @ 1 Hz 24 GMI Koch, Rosen, APL 78(13) 1897 (2001) n Planar fabrication n 80 p. T/ Hz @ 1 Hz Kawahito S. , IEEE J. Solid State Circuits 34(12), 1843 (1999)

Giant Magneto-impedance (GMI) Iac Magnetic amorphous wire Co. Fe. Si. B M Enhanced skin effect in magnetic wire frequency 25 GMI spec. external field “Giant magneto-impedance and its applications” Tannous C. , Gieraltowski, Jour Mat. Sci: Mater. in Electronics, V 15(3) pp 125 -133 (2004)

GMI specifications State variable B-field Vector Noise @ 1 Hz ~3 n. T/ Hz 1/f mag noise Temp fluct. M Johnson Perming sources Operating T 26 MR Z @ MHz RT Volume 0. 01 mm 3 wire Power Batter Commercial: ~100 $

Magneto-resistive (MR) sensors n n AMR - Anisotropic MR q Single ferromagnetic film - Ni. Fe q 2% change in resistance M Spintronic: q q 27 hdd FM GMR – Metal spacer FM n 60% DR/Rmin Co/Cu/Co NM n Parkin, APL (1991) FM TMR – Insulator spacer n 472% DR/Rmin at R. T. n Co. Fe. B/Mg. O/Co. Fe. B n Hayakawa, APL (2006) “Thin Film Magneto-resistive Sensors S. Tumanski, IOP (2001). * * I

MR sensors - high spatial resolution High Frequency n Data storage q HDD read head 100 Gb/in 2 q 1 GHz BW q < 100 p. T/ Hz from SNR Mg. O MTJ 100 p. T/ Hz ~100 nm ~150 28 MR NDE nm Frietas, Ferreira, Cardoso J. Phys. : Condens Mater 19 165221 (2007)

MR Sensors – non-destructive evaluation n 256 element AMR linear array n Thermally balanced bridges n High speed magnetic tape imaging – forensics, archival n NDE imaging 4 mm write head stop event Current flow in VLSI RAM w/short I+ I- V+ V 16 mm x 256 4 mm Cassette Tape – forensic analysis 2 cm 45 mm I- erase head +Ix event stop +Iy -Ix 29 da Silva, et al. , subm. RSI (2007)

MR biomolecular recognition 1. 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 “BARC” Bead Array Counter 30 MR sens. Device Applications Using SDT, Tondra et. al Springer Lecture Notes in Physics, V 593, 278 -289 (2002)

MR as low field sensors State variable B-field Noise @ 1 Hz sources Operating T Resistance Vector ~200 p. T/ Hz 1/f mag noise Temp fluct. M Johnson/Shot Perming RT Volume 0. 001 mm 2 film Power battery 31 F. C. Commercial: ~ $ AMR Honeywell Philips 2 Unshielded sensors GMR NVE 2 shielded Flux concentrators TMR “Low frequency picotesla field detection…” Chavez, et. al, APL 91, 102504 (2007).

The joy of flux concentrators Bext a TMR with F. C. 2 cm 32 Noise Need: Soft ferromagnet High M = c. H No hysterisis Þ Gain up to ~50 Þ No increase in noise L Increase in form factor

Spectral noise measurements 1 m 1 n 1 p 33 Hall FC without flux concentrator with external flux concentrator Stutzke, Russek, Pappas, and Tondra, J. Appl. Phys. 97, 10 Q 107 (2005) Yuan, Halloran, da Silva, Pappas, J. Appl. Phys. submitted (2007)

Integrated Hall sensors with flux concentrators Internal flux concentrators Hall element Noise @ 1 Hz (n. T/ Hz) White noise (f> 100 Hz) (n. T/ Hz) Hall with no flux concentrators* 300 200 Only internal flux concentrators 300 30 With both internal and 30 3 external flux concentrators 34 Hall spec. “Bridging the gap between AMR, GMR and Hall Magnetic sensors Popovic, et. al, PROC. 23 rd MIEL, V 1, NIŠ, YUGOSLAVIA, 12 -15 MAY, 2002

Hall Effect specifications V State variable Voltage B-field Vector Noise @ 1 Hz 300 n. T/ Hz I 30 n. T/ Hz w/FC’s Applications Operating T Power Form Factor RT In. As thin film Keyboard switches Brushless DC motors Very low Tachometers 0. 1 mm 2 - Si Flowmeters Commercial: ~$ 0. 1 1 35 disruptive B

Disruptive technologies? Superconducting flux concentrator State variable B-field Noise @ 1 Hz Operating T Power Form Factor 36 ME GMR voltage Hybrid S. C. /GMR Vector 32 f. T/ Hz cryogenic Line (cryogenics) Loop ~ 3 x 3 mm Field Gain YBCO ~ 100 Nb ~ 500 “…An Alternative to SQUIDs” Pannetier, et. al, IEEE Trans Super. Cond 15(2), 892 (2005)

Magneto-electric State variable B-field Noise @ 1 Hz sources Operating T Power Form Factor 37 MO Piezo voltage Vector 1 n. T/ Hz pyro/static Magnetostrictive + piezo-electric multilayer H PMN-PT -40 to 150 C 0 10’s mm 3 VME Terfenol-D Disruptive No power required Two terminal device High impedance output Dong, Zhai, Xin, Li, Viehland APL V 86, 102901 (2005)

Magneto-optic State variable B-field Noise @ 1 k. Hz Light intensity Vector 1. 4 p. T/ Hz Magnetometer head Fiberoptic Mirror-coated iron garnet B Ferrite Flux Concentrators • Light polarization changes in Garnet • Rotation B-field (Faraday effect) Operating T Power Form Factor ambient low 10’s cm 3 • Sensed with interferometer Disruptive • Light not affected by B • Remote sensors • High speed • Imaging capability • NDE Deeter, et. al Electronics Letters, V 29(11), p 993 (1993). 38 Spintronic Youber, Pinassaud, Sensors and Actuators A 129, 126 (2006).

Other spintronic sensors n Extraordinary MR (EMR) Semiconductor B Au impurity q Hall effect with metal impurity n q n Based on 106 MR in van der Pauw disks Non-magnetic materials q Mesoscopic device q DR/R ~ 35% in field I V In. Sb GMR replacement in hdds? q 39 Au Mg. O TMR in 2004 hit 220% … 300 nm “Magnetic Field Nanosensors, Solin, Scientific American V 291, 71 (2004)

Other disruptive technologies 40 concl n Magneto-strictive delay lines n More spintronics: CMR q Nano-wire q Spin-FET APL (2007)

Compilation Noise @ 1 Hz Sensor B SQUID vector . 01 line m Proton scalar 1 battery cm Electron vector 1 / 5 /. 001 battery/line cm /mm / m Fluxgate Sensor vector 10 battery 10 cm GMI vector 3000 battery 10 cm MR vector 200 small battery mm Hall vector 30, 000 battery 100 mm Magneto-electric vector 1000 0 Magneto-optic vector 41 pt/ Hz Power Length line Scale m

Conclusions 42 Ackn. n High sensitivity magnetometers research very active n Many advances to be made in conventional devices n Potentially disruptive technologies n Move to smaller, lower power, nanofabrication n Magnetic sensor technology is important

Acknowledgements n n n 43 Steve Russek Bill Egelhoff John Unguris n Mike Donahue n John Kitching n Fabio da Silva n Sean Halloran n Lu Yuan

x-y-z Hall sensors with internal flux concentrators 44 Schott, et al, IEEE p 978 (2004)

SQUID devices n Microfabrication n Nb/Al-Al. O/Nb Nb Al. OX ~ 1. 5 nm Al Nb JJ’s Superconducting shielded can 45