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

2 Applications Health Care Geophysical Astronomical Archeology Non-destructive evaluation (NDE) Data storage North Caroline Department of Cultural Resources “Queen Anne’s Revenge” shipwreck site Beufort, NC Mars Global Explorer (1998) Magnetic RAM Magneto-encephalography Magneto- Cardiography Bio-magnetic tag detection what

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

4 MR biomolecular recognition 1.Nano-scale magnetic labels that attach to target DNA 2.GMR arrays with probe DNA 3.Labels are sensed when probes attach to targets  Goal: high sensitivity chemical assays  Need high sensitivity magnetic detector arrays Device Applications Using SDT, Tondra et. al Springer Lecture Notes in Physics, V593, (2002) “BARC” Bead Array Counter MR sens.

5 MR as low field sensors State variableResistance B-fieldVector 1 Hz sources ~200 pT/  Hz 1/f mag noise Temp fluct. M Johnson/Shot Perming Operating TRT PowerLow Form Factor m2m2 AMR Honeywell Philips GMR NVE Commercial: ~ $ 2 Unshielded sensors 2 shielded Flux concentrators TMR “Low frequency picotesla field detection…” Chavez, et. al, APL 91, (2007). F.C.

6 The joy of flux concentrators B ext a Need: Soft ferromagnet High M =  No hysterisis  Gain up to ~50  Will it help other sensors? 2 cm Noise

7 Spectral noise measurements Si Hall Sensors Fluxgates AMR Hall FC