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High Sensitivity Magnetic Field Sensor Technology overview

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

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

  2. Outline • High sensitivity applications & signal measurements • Description of various types of sensors used • New technologies • Comparison of sensor metrics

  3. 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)

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. Benchmark properties: SQUID

  12. Superconducting Quantum Interference Devices Signal (V) I Superconductor B IR IL B(T) Tunnel Junctions Left-Right phase shifted by B PU loop

  13. 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

  14. SQUID Magnetometer Integrated Systems Discrete components Commercial: 10 – 100’s k$ “The SQUID Handbook,” Clarke & Braginski, Wiley-VCH 2004 MRI

  15. 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)

  16. 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

  17. Proton magnetometer • Kerosene cell • Toroidal excitation • & pickup Commercial: 5 k$ Olsen, et. al (1976) From Ripka, (2001) e- spin

  18. 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

  19. He4 e--spin magnetometer Smith, et al (1991) from Ripka (2001) JPL - SAC-C mission Nov. (2000) CSAM

  20. 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

  21. 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

  22. 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

  23. 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

  24. * * * * “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

  25. 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.

  26. 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

  27. 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

  28. Bext Fluxgate Drive(f) Pickup(2f) Bext M M H Hmod(f) Commercial: ~1 k$ “Magnetic Sensors and Magnetometers” P. Ripka, Artech, 2001 GMI

  29. 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.

  30. GMI specifications Commercial: ~100 $ Disruptive

  31. 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

  32. 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

  33. 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

  34. 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

  35. Compilation Trend: Noise increases as Volume decreases Bn vs. V

  36. 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

  37. 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.

  38. Acknowledgements • Steve Russek • Bill Egelhoff • John Unguris • Mike Donahue • John Kitching • Fabio da Silva • Sean Halloran • Lu Yuan • Jeff Kline

  39. 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

  40. 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)

  41. 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

  42. 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

  43. 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

  44. 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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