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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. Market analysis - magnetic sensors. 2005 Revenue Worldwide - $947M Growth rate 9.4%. Application. Type.

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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. 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)

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

  4. Magneto-encephalography Bio-magnetic tag detection Magneto- Cardiography Magnetic RAM Mars Global Explorer (1998) North Caroline Department of Cultural Resources “Queen Anne’s Revenge” shipwreck site Beufort, NC JPL - SAC-C mission Nov. (2000) “Biomagnetism using SQUIDs: Status and Perspectives” Sternickel, Braginski, Supercond. Sci. Technol. 19 S160–S171 (2006). Frietas, ferreira, Cardoso, Cardoso J. Phys.: Condens. Mater 19, 165221 (2007) Applications • Health Care • Geophysical • Astronomical • Archeology • Non-destructive evaluation (NDE) • Data storage SI units

  5. “Magnetic field intensity”: H-field A/m A B-field tesla (T) kg/(As2) H = ~0.1 A/m B = 210-7 T e.g. 1 A @ 1 m Flux - F = BA SI - Le Système International d’Unitès • What do we measure? B = flux density = “Magnetic induction” field r (m) I (A) Use m0 = permeability of free space B = m0 H Frequency

  6. B-field Ranges & Frequencies 1 mT 1 gauss  10-4 T ~ Earth’s B-field 1 mT 1 A @ 1 m Industrial 1 nT Geophysical Geophysical Industrial/NDE Magneto- cardiography 1 nT Magnetic field Range B-field Magnetic Anomaly Magneto-cardiography 1 pT Magnetic Anomaly 1 pT Magneto- encephalography Magneto- encephalography 1 fT 1 fT 1 1 100 100 10,000 10,000 0.0001 0.0001 0.01 0.01 Frequency (Hz) Frequency (Hz) Adapted from “Magnetic Sensors and Magnetometers”, P. Ripka, Artech, (2001) effects

  7. 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

  8. 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

  9. Bext  Bf State measurement S • Low noise excitation source - • Voltage, current, light, … • Detector volume -  = Ah • Sense state • Flux feedback is typical • Linearize • Dynamic Range • Complicated • Limits slew rate & bandwidth A h S B Noise

  10. Units 100,000 1/f 10,000 1,000 White 100 State Measurement 10 1 Noise metrology • Magnetically shielded container (or room) • Low noise preamplifiers • Spectrum analyzer – P = V2/Hz • field noise = power / sensitivity Low TCSQUID magnetometer (w/gradiometer) f T/Hz 0.01 0.1 1 10 100 Hz Preamp Benchmarks

  11. Benchmark properties: SQUID

  12. Superconducting Quantum Interference Devices Signal I Superconductor B B IR IL 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 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 MKG

  15. ~60 pT Real time magneto-cardiographywith SQUID magnetometer Oh, et. al JKPS (2007) Resonance

  16. Resonance magnetometers f  Bext • Nuclear spin resonance • Protons • water, methanol, kerosene • Overhauser effect: • He3, Tempone • Electron spin resonance • He4,Alkali metals (Na, K, Rb) Bext Proton

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

  18. Bext Electron spin magnetometers Photodetector f~ MHz for e- Vapor cell RF Coils l/4 Filter Laser Budker, Romalis, Nature Physics, 3(4), 227-234 (2007) He4

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

  20. 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

  21. 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

  22. 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

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

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

  25. 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.

  26. GMI specifications Commercial: ~100 $ MR

  27. * * * * “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 • 472% DR/Rmin at R.T. • CoFeB/MgO/CoFeB • Hayakawa, APL (2006) M FM NM FM Forensics

  28. 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)

  29. MR biomolecular recognition • Nano-scale magnetic labels that attach to target • GMR arrays with probe • Probes attach to targets Need very sensitive magnetic detector arrays  Goal: high accuracy chemical assays “BARC” Bead Array Counter Device Applications Using SDT, Tondra et. al Springer Lecture Notes in Physics, V593, 278-289 (2002) MR sens.

  30. Flux concentrators MR as low field sensors AMR Large area films 2 Unshielded sensors GMR Small sensors 2 shielded TMR Commercial: ~ $ “Low frequency picotesla field detection…” Chavez, et. al, APL 91, 102504 (2007). F.C.

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

  32. 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) Hall FC

  33. Integrated Hall sensors with flux concentrators Internal flux concentrators Hall element “Bridging the gap between AMR, GMR and Hall Magnetic sensors Popovic, et. al, PROC. 23rd MIEL, V1, NIŠ, YUGOSLAVIA, 12-15 MAY, 2002 Hall spec.

  34. B Hall Effect specifications V I InAs thin film Applications Keyboard switches Brushless DC motors Tachometers Flowmeters    Commercial: ~$ 0.1  1 Disruptive - hybrid

  35. Disruptive technologies?Superconducting flux concentrator Hybrid S.C./GMR Field Gain YBCO ~ 100 Nb ~ 500 “…An Alternative to SQUIDs” Pannetier, et. al, IEEE Trans SuperCond 15(2), 892 (2005) ME

  36. Magneto-electric Magnetostrictive + piezo-electric multilayer H PMN-PT VME Terfenol-D Disruptive No power required Two terminal device High impedance output Dong, et. al APL V86, 102901 (2005). Hristoforou, Sensors and Actuators A132 (2006) . MO

  37. 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

  38. More spintronic sensors… B Semiconductor • Extraordinary MR (EMR) • 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? • 220% TMR in 2004 … Au impurity Au V I InSb “Magnetic Field Nanosensors, Solin, Scientific American V291, 71 (2004) CMR

  39. 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–R150 Transistors

  40.  Spin transistors • Tunnel junction based devices van Dijken, et. al, APL V83(5) 951 (2003) Spin dependent hot e- transmission • CuTunnel BarrierSpin ValveSchottky barrier • 3400% magneto-conductance at 77 K • Relatively low currents (10 mA), 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

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

  42. Bnoise vs. Volume Hall GMI ME MR Proton CSAM Fluxgate He4 MO Hybrid SQUID SERF Magn. Sensors

  43. 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

  44. Compare sensors based on volumetric energy resolution • Energy resolution  Noise Power  Volume  S.C. F.M D. Robbes / Sensors and Actuators A 129 (2006) 86–93 Conclusions

  45. 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.

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

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