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High Sensitivity Magnetic Field Sensor Technology

Explore cutting-edge magnetic sensor advancements with high sensitivity applications, noise and signal measurement techniques, various sensor types, and flux concentrator usage. Discover applications in healthcare, geophysics, astronomy, archaeology, and data storage. Delve into magnetometer technologies, state measurement methods, and noise metrology tools for real-time magneto-cardiography and more. Learn about benchmark properties of Superconducting Quantum Interference Devices (SQUIDs) and commercial resonance magnetometers. Witness innovations in fluxgate technology with micro-fluxgates and circumferential magnetization techniques.

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High Sensitivity Magnetic Field Sensor Technology

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  1. High Sensitivity Magnetic Field Sensor Technology 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 • Noise & signal measurement • Description of various types of sensors • Addition of flux concentrators • Summary

  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 Applications • Health Care • Geophysical • Astronomical • Archeology • Non-destructive evaluation (NDE) • Data storage

  5. B-Field Ranges & Frequencies Industrial 1 nT 1 nT Geophysical Geophysical Industrial/NDE Magneto- cardiography Magneto- cardiography Magnetic field Range 1 pT 1 pT B-field Range Magnetic Anomaly Magnetic Anomaly 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) F.L. Fagaly Magnetics Business & Technology Summer 2002 Adapted from “Magnetic Sensors and Magnetometers”, P. Ripka, Artech, (2001)

  6. Magnetic field strength: H-field in A/m What is actually measured? Magnetic induction field, B (flux density) What are we measuring?Systèm International d’Unitès r (m) I (A) B = m0 H B-field in tesla (T)

  7. B-fields… • Induce currents in conductors • 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

  8. Magnetometer technologies • Induction • Search Coil • Fluxgate • Scattering • Magneto-resistive, Impedance, Optical, Electric… • Spintronic – Giant MR, Tunnelling MR • Hall Effect • Superconducting • SQUIDS • Spin Resonance • Proton, electron

  9. Bext  Bf State measurement • Low noise excitation source - • Voltage, current, light, … • Sense state with detector • Flux feedback is typical • Linearize • Dynamic Range • Complicated • Limits slew rate & bandwidth S B

  10. 100,000 10,000 1,000 100 10 1 Noise metrology • Magnetically shielded container • Low noise preamplifiers • Spectrum analyzer – P = V2/Hz • power / sensitivity = field noise SQUID Magnetometer State Measurement f T/Hz 0.01 0.1 1 10 100 Hz

  11. ~20 pT 1pT/Hz 1 10 100 1000 .01 0.1 1 10 100 Real time magneto-cardiography High TC SQUID – 1pT/Hz @ 1 Hz Low TC SQUID – 10 fT/Hz @ 1 Hz Oh, et. al JKPS (2007) 1 pT/Hz

  12. Benchmark properties:

  13. Superconducting Quantum Interference Devices I Signal B IR IL B Tunnel Junctions Left-Right phase shifted by B

  14. Pickup loops for SQUIDS • One loop – measure BZ • Two opposing • dBZ/dz (1st order gradiometer) • Good noise rejection • Three – alternating • dBZ2/dz2 (2nd order gradiometer) • High noise rejection N S

  15. SQUID Magnetometer “The SQUID Handbook,” Clarke & Braginski, Wiley-VCH 2004 Commercial: 10 – 100’s k$

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

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

  18. B Electron spin magnetometers Photodetector • Standard cell • Chip scale atomic magnetometer (CSAM) • Rb metal vapor • Spin-exchange relaxation free (SERF) • K metal vapor Vapor cell RF Coils l/4 Filter Laser Budker, Romalis, Nature Physics, 3(4), 227-234 (2007)

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

  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).

  21. e--spin magnetometer Spin-exchange relaxation free • K metal vapor • Low field, high density gas • Line narrowing effect • =>Optimized for high sensitivity • All –optical pump/probe Kominis, et. al, Nature 422, 596 (2003)

  22. Ferromagnetic magnetometers • Fluxgate • Magneto-resistive • AMR – Anisotropic MR • GMR – Giant MR • TMR – Tunneling MR • Giant Magneto-impedance • Magneto-striction

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

  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 Kawahito S., IEEE J. Solid State Circuits 34(12), 1843 (1999) Koch, Rosen, APL 78(13) 1897 (2001)

  25. * * * * Magneto-resistive (MR) sensors I FM • AMR - Anisotropic MR • Single ferromagnetic film • 2% change in resistance • GMR – Cu spacer • Up to 60% change • TMR – Insulator spacer • Insulator => 400% change M FM NM FM “Thin Film Magneto-resistive Sensors S. Tumanski, IOP (2001).

  26. MR sensors - high spatial resolutionHigh Frequency • Data storage • HDD read head 100 Gb/in2 • 1 GHz BW • < 100 pT/Hz from SNR MgO MTJ 100 pT/Hz ~150 nm Frietas, Ferreira, Cardoso, Cardoso J. Phys.: Condens Mater 19 165221 (2007)

  27. I+ I- I- V+ V- 16 mm Ferrofluid image MR Sensors – scalability & imaging • 256 element AMR linear array • Thermally balanced bridges • Image magnetic tapes real time – forensics, archival • NDE imaging Cassette Tape – forensic analysis

  28. MR biomolecular recognition • Nano-scale magnetic labels that attach to target DNA • GMR arrays with probe DNA • Labels are sensed when probes attach to targets => Goal: high sensitivity chemical assays “BARC” Bead Array Counter Device Applications Using Spin Dependent Tunneling and Nanostructured Materials M. Tondra, D. Wang, Z. Qian, Springer Lecture Notes in Physics, V593, 278-289 (2002)

  29. Flux concentrators MR as low field sensors AMR Honeywell Philips 2 Unshielded sensors GMR NVE 2 shielded TMR “Low frequency picotesla field detection…” Chavez, et. al, APL 91, 102504 (2007). Commercial: ~ $

  30. 2 cm The joy of flux concentrators Bext a • Need: • Soft ferromagnet • High M = cH • No hysterisis • Gain up to ~50 • Will it help other sensors?

  31. Spectral noise measurements Si Hall Sensors AMR Fluxgates

  32. +external x10 Internal F.C. x10 Hall, no F.C. Integrated Hall sensors with flux concentrators X 100 improvement with flux concentrators 10-9 10-6 10-3 Magnetic field Popovic, et. al, PROC. 23rd MIEL,, VOL 1, NIŠ, YUGOSLAVIA, 12-15 MAY, 2002

  33. Hall Effect specifications V I InAs thin film Applications Keyboard switches Brushless DC motors Tachometers Flowmeters    Commercial: ~0.1 (sensors) - 1 (integrated) $

  34. 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)

  35. Magneto-electric Magnetostrictive + piezo-electric multilayer H PMN-PT VME Terfenol-D Disruptive No power required Two terminal device High impedance output Dong, Zhai, Xin, Li, Viehland APL V86, 102901 (2005)

  36. Iac Magnetic amorphous wire M Enhanced skin effect in magnetic wire frequency  external field  H Giant Magneto-impedance (GMI) CoFeSiB “Giant magneto-impedance and its applications” Tannous C., Gieraltowski, Jour Mat. Sci: Mater. in Electronics, V15(3) pp 125-133 (2004)

  37. GMI specifications Commercial: ~100 $

  38. Other disruptive technologies • Magneto-strictive delay lines • Magneto-optic sensors • Other spintronic devices

  39. Conclusions • High sensitivity magnetometers research very active • Many advances to be made in conventional devices • Potentially disruptive technologies pursued • Move to smaller, lower power, nano-fabrication

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

  41. Spin Transistors

  42. Magneto-optic

  43. Search Coils

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

  45. Bound Current Bint~10Bext Bext Bg~Bint M Bext The joy of flux guides: For small gap: Bg ~ 10 Bext “soft” ferromagnet

  46. SQUID devices Nb AlOX ~ 1.5 nm Al • Microfabrication • Nb/Al-AlO/Nb Nb JJ’s Superconducting shielded can

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