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Magnetic Sensors and Magnetic Magnetic Sensors and Magnetic ActuatorsActuators

Digital Compass SolutionCombines a two axis MR Magnetic Sensors in order to detect the magnetic field.Use in wireless phone, vehicle compassing and antenna Positioning.

February 2005

GMR head Structure

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Different types of Magnetic Different types of Magnetic Sensors and Magnetic ActuatorsSensors and Magnetic Actuators

Magnetic Actuators• Microinductance• Actuators

Magnetic Sensors• Inductive sensor • Hall sensor• Magnetoresistance (MR)• Giant Magnetoresistance (GMR)• FluxGate

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UnitsUnitsMagnetic Induction: Tesla: T Magnetic Induction: Gauss = 10-4 TMagnetic field: A.m-1. Magnetic Field Oersted: 1 A.m-1 = 4. pi.10-3 OeMagnetic flux: 1T.m2 = 1 wb Permeability: 4.pi.10-7

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Characteristics of Magnetic Characteristics of Magnetic SensorsSensors

Measurement Magnetic Field

Range (mT)

Sensitivity(nT)

FrequencyRange (Hz)

Applications

Inductive Effect 10-10 à 106 Depend of applications

0.1 to 107 Detection of variable

Magnetic Field

Hall effect 0.1 à 3.104 100 0 to 100 M Ratiometric linear sensor

(Current sensor)

MRAnd GMR

 10-3 à 5

 10

 0 to 10 M

More sensitive than Hall Effect but less linear(Compasses)

« Fluxgate » 10-4 à 0.5 0.1 0 to 10 k VectorialMagnetometer (compasses)

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Inductive SensorsInductive SensorsInductance to generate or to measure a magnetic field

Applications:• NMR (Nuclear Magnetic Resonance)• NDE, Isolator

ADuM1100

Electroplating

NDE (Non Destructive Evaluation)Model of the inductor

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Hall Sensors: PrincipleHall Sensors: PrincipleMagnetic effect in a long sample l>>w

eEpdpv

.

p mobility

Current density

eEpeE

qp=.=p

J

pF

Bdpve

Magnetic Force

Drift velocity

The magnetic force push carriers toward the upper edge of the strips. Electricity behaves somewhat like an incompressible fluid. It reacts bydeveloping an electric field, the Hall field that counterbalances exactly the magnetic pressure exactly.

p carriers density

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Hall SensorsHall SensorsThe Hall electric field is:

BdvB

dve

-=

HE0=

HE e+

wBeEp

wdz ..HEHV

The Hall voltage is:

yBp

eEHE

HP tan

J

Hp

E

E H

E e

B

Hall angle: Hall coefficient:

RqpHp 1

BItpqH

V ...

1

The Hall voltage depend of:

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Hall Sensors: Optimization 1Hall Sensors: Optimization 1

BItpq

wBeEp .

..

1.HV

  InAs InSb AsGa

n (cm2/Vs) 33000 78000 8500

p (cm2/Vs) 460 750 400

In order to increase the sensitivity, these materials are use:

Different sorts of errors for Hall sensors:• Scattering of the sensitivity of the Hall voltage• Dependence of the Hall voltage with the temperature• Inductive effect• Offset, linearity

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Hall Sensors: Optimization 2Hall Sensors: Optimization 2

V

Is

p

BBm

Linearity Offset Inductive effect

e SdB

dt .

Magnetic sensor placed near the electronicin order to correct the errors of the HallSensor.

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Hall Sensors: ApplicationsHall Sensors: Applications

Voff dS

dB

  

Reference

 Magnetic

Field Range (T)

 offset Voff

  

Sensitivity S mV.mT-1

 For 1 degree

 For 1 degree

   frequency

cut-off

  Price

(euros)1 piece

KSY14Siemens

 non defined

 15 mV

 1.05 à 1.6

 0.03%

 0.3%

 0.7%

 Above 1

MHz

  6

UGN3503Allegro

With electronic

  

non defined

  

2.5 V

  

7.5 à 17.2

 0.05% pour

0.05 mT

  

stable 

  

2%

  

23 KHz

  7

SS495A1Honeywel

lWith

electronic

 

-0.06 to 0.06

  

2.5V

  

31.25 3%

  

0.03%

  

0.04%

 

1%

 

50 KHz

  7

SS94A2Honeywel

lWith

electronic

 

-0.05 to 0.05

  

4V

 

5 2%

  

0.02%

  

0.02%

  

0.8%

 

100 KHz

  30

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Magnetoresistance: PrincipleMagnetoresistance: PrincipleMagnetic effect in a short sample l<<w

Current density

As, Jp(B) are present on the two sidesof this equation, we can simplified:

Lorentz Force

E e

BvqEqEq

BvqEqF

nen

nen

BBJJBJ pppp 0

J B

J J B B J B

Bp

p p p p p p

p

0 0 0

12

J BB

E E Bp

p

e p e

12

Jp(0) and B are perpendicular

The path of the current in the sample depend of the external magnetic field. So the resistance depend of the magnetic field.

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MagnetoresistanceMagnetoresistance

Dependence of R/R0 function of B

12

B p

The term show that the resistivity depend of B.

InSb :Antimoine d’IndiumNiSb : Antimoine de Nickel

This type of sensor are not largely use becauseThe characteristics of the magnetoresistance anisotropic are better.

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Magnetoresistance Magnetoresistance AnisotropicAnisotropic

The anisotropy is obtained during the fabrication of the material. It is applied a magnetic that caused a preferred path for the magnetic field.During the step of sputtering on a thin film like Permalloy (FeNi 20% 80%, a magnetic field is applied and this introduce a easy path. This magnetic field introduce a easy axe and a magnetization of the thinFilm.

M: MagnetizationI: CurrentH: External magnetic field

We will show that the resistance depend of the angle and

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AMRAMR

In order to simplify, we suppose that H is applied in the direction of Hy.

• The resistance decrease with the magnetic field.• The magnetic sensor is not linear.• It is also impossible to determine the sign of the magnetic field.

0sin

H

yH

2max cos.)( RRHR and

If I is align with the easy axis:

= -. So, 0yHpour

2

01cos H

H

yH

2

0max 1.)(

H

HRHR y

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AMR with Barber polesAMR with Barber poles

If I is align at 45 degrees: 45 = +

2sin1cosasincos2

245cos nd

2

00

12

2cos

H

H

H

H yy

2

00

max 1212

)(H

H

H

HRRHR yy

2

00max 1

2

1)(

H

H

H

HRHR yy

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AMR: RealizationAMR: Realization

V b

V 0

H y

H z2

01

000

H

yH

H

yH

R

RV

bV

S

KMZ10A  Reference

 Magnetic

field range(T)

Sensitivity S:mV.mT-1

Supplied with 5 V

for 1 degree  Bridge

Resistance

 KMZ10A

Philips

 -0.625 mT to +0.625 mT

 64

 -0.15 %.°C-1

 1.3 K

 KMZ10C

Philips

 -3.75 mT to +3.75 mT

 6

 -0.15 %.°C-1

 1.7 K

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GMR: PrincipleGMR: Principle

Sandwich with one ferromagnetic layer and one non magnetic layer.

FeCr, FeNiAg, FeNiCu with thickness Fe = 30 A et Cr = 9 A

With BWithout B

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GMR: PrincipleGMR: Principle

With BWithout B

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GMRGMR

Realization (NVE)

 Reference Range (T)

 Offset Voff

Sensitivity mV.mT-1

supplied with 1V

 Linearity

 Resistance

k

 NVS5B15

 1,5m

 0 4mV

 30 à 44

 2%

 5 20%

 NVS5B50

 5m

 0 4mV

 9 à 13

 2%

 5 20%

 NVS5B100

 10m

 0 4mV

 4,5 à 6,5

 2%

 5 20%

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Applications of AMR and GMRApplications of AMR and GMR

Measurement of current Detection of the speed

Anisotropic Magnetoresistance (AMR)

0.5%/Oe 1-100 µm 0.1 Oe

SensitivitySensitivity SizeSize ResolutionResolution

Giant Magnetoresistance (GMR) 1%/Oe 1-100 µm 0.01 Oe

Wire FeCoNi electroplated (GMI) 500%/Oe 1-2 mm 0.000001 Oe

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FluxGate: PrincipleFluxGate: PrincipleThe first winding is used to saturate the magneticMaterial. When the magnetic material is saturate,there is no voltage across the second winding.

Measurement of delay introduce on the voltage across the second winding will be help to determine the value of the magnetic filed. When there is no magnetic field, the gap between the pulse is constant. When a magnetic field is applied, the gap between the two pulses are different.

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FluxGate: RealizationFluxGate: RealizationConfiguration of the windings

The fluxgate is very sensitive. The realization is complex but magnetic sensors with low sensitivity have good perspective.

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Magneto Impedance: MIMagneto Impedance: MIPrinciple: Use the skin effect

A current in a wire cause that the current density is concentrate at the periphery of the wire. So the impedance of the wire increase with the frequency. A external magnetic field cause also a dependence of the impedance with the magnetic field.The purpose is to polarize the wire at a frequency and the external magnetic field cause a variation of the impedance.

f 1

CharacteristicsPolarization at 10 MHz. Range of B from nT to µT.Sandwich of Layers: FeCoSiB: 40 µm thickness.Wire: CoFe: 30 µm diameter.

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Magnetic ActuatorMagnetic Actuator

Magnetic materialPermalloy FeNi electroplated.MagnetThe magnet is placed under the micro inductance. It is glued or electroplated.

Micro InductanceConductor (Al, Cu) deposed on a substrateglass or Si. The size, the number of turnsgive a inductance value. The thickness of the conductor must be important. The conductorneed to be deposed by electroplating in a molding.Current density increase with the reduction of the size of the conductor (1000 A.mm-2

for a wire with a µm dimension).

A micro Inductance is used to generate a magnetic field. This magnetic field act on a magnetic layer in order to develop a force.

MAGMAS: Magnetic micro actuator and system

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2D Optical Switch Array for Optical 2D Optical Switch Array for Optical RoutingRouting

A mirror move when a current is applied on the micro inductance. It reflect the lighttransmit with the optics fiber. Under the membrane, the permalloy is electroplated.

Under the coil, a magnet is placed. A pulse in the coil shift the mirror. When the signalis interrupted, the mirror stay in position. When another pulse is applied on the coil, themirror move.

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BibliographieBibliographie

About Hall Sensors: Hall Effect Devices RS POPOVICS (Library).About GMR: Magnetic Multilayers and Giant Magneto-resistance, Springer, Surface Sciences (Library).