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High Sensitivity Magnetic Field Sensor Technology

David P. Pappas

National Institute of Standards & Technology

Boulder, CO

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Applications

Health Care

Geophysical

Astronomical

Archeology

Non-destructive

evaluation (NDE)

Data storageNorth 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

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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

IMFM

FM

NM

FM

**

*

*“Thin Film Magneto-resistive SensorsS. Tumanski, IOP (2001).hdd

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MR biomolecular recognition1. 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. alSpringer Lecture Notes in Physics, V593, 278-289 (2002)

“BARC”BeadArray Counter

MR sens.

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MR as low field sensors State variable Resistance

B-field Vector

Noise @ 1 Hz

sources

~200 pT/Hz1/f mag noiseTemp fluct. MJohnson/Shot

Perming

Operating T RT

Power Low

Form Factor m2

AMRHoneywell

Philips

GMRNVE

Commercial: ~ $

2 Unshielded sensors

2 shielded

Fluxconcentrators

TMR

“Low frequency picotesla field detection…”Chavez, et. al, APL 91, 102504 (2007).F.C.

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The joy of flux concentrators

Bext a

Need:

Soft ferromagnet

High M = No hysterisis Gain up to ~50 Will it help other sensors?

2 cm

Noise

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Spectral noise measurements

10-1 100 101 102 103 10410-13

10-12

10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

GMRNIST MTJ

GMI

Si Hall Sensor

coil 2.5 cm x 5 cm

Fluxgate

MTJ 1HW AMR

Fie

ld N

oise

Flo

or (

T/H

z1/2 )

Frequency (Hz)

GMR

Si Hall Sensors

Fluxgates

AMR

Hall FC