[PPT] - MEMS : an overview - What ? why ? how ? - Magnetic MEMS PowerPoint Presentation

SLIDE 1

MEMS : an overview

What ? – why ? – how ?
Magnetic MEMS

Nora M. Dempsey Institut Néel, CNRS/UJF, Grenoble, France

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Micro-magnets for MEMS

Candidate Hard Magnetic Materials
Preparation routes
Micro-fabrication
Beyond magnets

1/28

SLIDE 2

What are MEMS ?

MEMS : “Micro-Electro-Mechanical Systems” “Microsystems Technology” (MST) “Mecatronics”

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

machines which range in size from µm to mm e.g. actuators, motors, generators, switches, sensors….

Common examples

inkjet printer heads (ink ejection)
accelerometers ( airbag deployment…)
gyroscopes ( trigger dynamic stability control…)
pressure sensors (car tires, blood…)
displays (DLP video projectors…)
optical switching technology (telecommunications)

electrostatic, thermal, piezoelectric, piezoresistive, capacitive, magnetic…

2/28

SLIDE 3

Domains of application

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Bio-technologies less-invasive surgery, µ-injections, lab-on-chip, ophtalmology… Data storage µ-positionner for HDD heads motorisation for HDD Telecommunications µ-switch for mobile phones commutators for optic fibre networks Automotive Aeronautics (Glass-cockpit…) Space (1 kg = 20 k$!) Consumer electronics media players, gaming devices, footpods..

3/28

SLIDE 4

Why are MEMS of interest ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

INTELLIGENT SYSTEMS: MEMS (eyes + arms + legs) + ELECTRONICS (brain) SIZE : small and light ! portable applications - mobile phones, aerospace devices … limited space applications - implantable devices, micro-surgery….. COST : batch processing ⇒ cheap ENERGY EFFICIENCY : they use little power themselves, + they can be used to improve efficiency in bigger systems (cars, houses..). MEMS sensor MEMS actuator Energy Electronics Signal processing Communication

4/28

SLIDE 5

effects not exploitable at the macro-scale can become of interest at the micron-scale

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Why size matters…..

Surfaces effects dominate at small scales

5/28

SLIDE 6

Scaling laws

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Gravitational force (weight) Electrostatic force ∝ L3 ∝ L2

W

6/28

SLIDE 7

Scaling laws for different forces

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Weight Capillary force Van der Waals force Length

∝ L3 ∝ L2

For MEMS, weight is negligible, surface forces may cause movement or deformation: electrostatic force can be used for actuation (controlable) capillary force can lead to MEMS failure (during fabrication or use) Van der Waals force can lead to stiction

Electrostatic force 7/28

SLIDE 8

Scaling laws

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

size reduction increases decreases

resonance frequency

∝ 1/L

response time

(e.g. thermal exchange)

stiffness
power consumption

8/28

SLIDE 9

How are MEMS made ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Building block for MEMS fabrication : I – Deposition II - Lithography III – Etching

MEMS are made with techniques originally developed for the microelectronics industry

9/28

SLIDE 10

How are MEMS made ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Building block for MEMS fabrication : I – Deposition II - Lithography III – Etching

MEMS are made with techniques originally developed for the microelectronics industry

SLIDE 11

Deposition

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

chemical reaction:

Chemical Vapor Deposition

(CVD)

Electrodeposition
Thermal oxidation

physical reaction:

Physical Vapor Deposition

(PVD)

Casting

10/28

SLIDE 12

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Chemical Vapor Deposition

Low Pressure CVD (LPCVD)

deposition on both sides of wafer

Plasma Enhanced CVD (PECVD)

deposition on one side of wafer

hot-wall LPCVD reactor

Chemical deposition

Electrodeposition

restricted to electrically conductive materials Well suited to Cu, Au, Ni 1µm to >100µm !!! hazardous byproducts !!!

11/28

SLIDE 13

Physical Vapor Deposition (PVD)

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

far more common than CVD for metals (lower process risk, cheaper material costs)

Evaporation

heating : e-beam or resistive - material specific

Sputtering

ion bombardment (Ar+) of target material released at much lower T than evaporation Well suited to alloys

12/28

SLIDE 14

Casting

material dissolved in a solvent and applied to the substrate by spraying or spinning
used for polymers, photoresist, glass
thicknesses: from a single monolayer of molecules to tens of µm

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

13/28

SLIDE 15

How are MEMS made ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Building block for MEMS fabrication : I – Deposition II - Lithography III – Etching

MEMS are made with techniques originally developed for the microelectronics industry

SLIDE 16

Lithography

Resolution: Optical UV ≈ 0.5 µm Deep UV ≈ 0.3 µm E-beam < 100 nm

14/28

SLIDE 17

Pattern transfer

lift-off approach less common because resist is incompatible with most MEMS deposition processes (high temperatures + contamination)

15/28

SLIDE 18

How are MEMS made ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Building block for MEMS fabrication : I – Deposition II - Lithography III – Etching

MEMS are made with techniques originally developed for the microelectronics industry

SLIDE 19

Dry etching

3) Vapor phase etching

material is dissolved at the surface in a chemical reaction with gas molecules e.g. HF for etching Si02 XeF2 for etching Si

1) Sputter etching - similar to sputtering deposition 2) Reactive ion etching (RIE)

accelerated ions react at surface – have both chemical and physical etching deep-RIE → hundreds of microns + almost vertical sidewalls, aspect ratios ≤ 50 : 1

"Bosch process"

alternates repeatedly between two gases: gas # 1: deposition of a chemically inert passivation layer (polymer) gas # 2: etches, polymer on horizontal surfaces is immediately physically sputtered while sidewalls not sputtered 16/28

SLIDE 20

Etching

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

Wet etching

material is dissolved in a chemical solution dry etching expensive much higher resolution High aspect ratio (≤ 50 : 1) wet etching simple and cheap vs

17/28

SLIDE 21

MEMS technologies

Bulk micromachining

defines structures by selectively etching inside a substrate,

typically Si is used and wet etched with KOH or TMAH

relatively simple and inexpensive

Surface micromachining

deposition / etching of different layers on a substrate
many fabrication steps (expensive)
can produce complicated devices

LIGA : x-ray Lithographie-Galvanoformung-Abformung (x-ray Lithography-Electrodeposition-Moulding) x-ray litho. of PMMA to produce template for electro-dep. (e.g. Ni) the electrodeposited structure may be used as a mould for replication from another material ( plastic, ceramic)

small, but relatively high aspect ratio devices

18/28

SLIDE 22

Why is magnetism of interest for MEMS ?

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

SLIDE 23

Remarkable features of magnetic interactions

1/ µ0 = 8.105 => 400 000 J/m3 @ 1 T ε0 = 9.10-12

=> 40 J/m3 @ 3 MV/m

Contactless actuation Remote / Wireless actuation Medical implantable Action through sealed membranes / vaccuum / skin Suspension / Levitation Large forces Magnetic pressure = 4 bar / Tesla² = 400 mN/mm2 / T2 Large energy densities (Bi)stability Magnets : permanent forces without power waste Long term forces - Safety Bidirectionality Repulsion / Attraction Long range Several 10 to 100 µm or more

Magnetic: ½B²/µ0 => 400 000 J/m3 @ 1 T Electrostatic : ½ε0E² => 40 J/m3 @ 3 MV/m

(elect. breakdown in air) 19/28

SLIDE 24

0.9 T 0.6 T 0.3 T 0 T

∆ : 0.3 T

1 mm

∆ : 0.3 T

10 mm ZOOM

Gradient x Moment = Force

/10 =

x10 x10

=

∆(Field) / Distance = Gradient topology of field preserved:

Homothetical scale reduction :

1 cm3 J = 1 T 1 mm3 J = 1 T H1 M ( ) →  v1 4 π ⋅ µo ⋅ r3 ⋅ 3 J1 r ⋅ ( ) →  r2 ⋅ r → ⋅ J1 −

       

→  ⋅ :=

P

r P Magnitude and

H

0.9 T 0.6 T 0.3 T 0 T

Gradient x L Force x L Field gradients & forces between magnets = increased Torque preserved

20/28

SLIDE 25

Laplace/Lorentz forces by a magnet onto a current

F B i

F= i. ℓ ∧

∧ ∧ ∧B

same current density x same field = same force density

21/28

SLIDE 26

Effects of a scale reduction 1 / L on conductor / conductor interactions (volumic, massic)

(at constant current density)

⇒ F/volume ∝ J².s.s. ℓ /R .d3

∝ 1/L

reduced

s

F = B. i. ℓ F = 2.10-7.i1.i2. ℓ /R

ℓ

i = J.s (infinite wire) H = i / 2πR B = µ0H = 4π10-7 . J.s / 2πR

∝ J.d²/d ∝ 1/L

reduced

H i

2

F

R

22/28

SLIDE 27

/ L² × frequency / L / L

current

/ L × frequency × L × L

magnet induction

e = -dΦ /dt

iron current magnet

Scale reduction 1 / L

Effects of a scale reduction 1 / L

n magnetic interactions (volumic, massic)

(at constant current density)

23/28

SLIDE 28

Surface thermal flow Φ/s = λ.∆T/e

Cylindrical wire = S/V min Heat generation RI² = volume = d3 Conductor = metallic thin film Distance between thermal sources = d

Classical electrotechnics : 5 A/mm² DC… Integrated µ-coils : up to 1 Million A/mm² in pulses!

Short time constants = current pulses = µs => S/V ratio = d²/d3 = 1/d : improves with scale reduction factor L Heat dissipation = surface = d² ⇒ Thermal gradient = x L ⇒ heat flow through surface = x L => S/V ratio increases also Planar conductor = S/V max Si substrate = excellent heat conductor/absorber

µ-coils can withstand gigantic current densities

thanks to better cooling

24/28

SLIDE 29

× L²i / L² × frequency × L²i / L × L²i / L × Li

current

/ L × frequency × L × Li × L

magnet induction

e = -dΦ /dt

iron current magnet

Scale reduction 1 / L

Effects of a scale reduction 1 / L

n magnetic interactions (volumic, massic)

with increased current density x Li

25/28

SLIDE 30

10 100 1000 10,000 100,000

Current density (A/mm²)

10 µm 100 µm 1 mm 10 mm

size

???

coil

magnet 1 Tesla Everyday life high-tech electrotechnics Superconductors, µ-coils Well cooled Silicon

??? < µs

A µ-magnet is much more interesting than a µ-coil/µ-electromagnet of same size

The importance of µ-magnets

coil

H H = N.i / ℓ (A/m) i = J.s = J.π R² H = N.J.π R² / ℓ 2R ℓ

coil Coil + Fe core

26/28

SLIDE 31

Some examples of magnetic MEMS…..

SLIDE 32

Deformable mirror for adaptive optics

(astronomy, ophtalmology…)

Si wafer Array of planar micro-coils Silicon waffer membrane coils magnets

LEG - LAOG - LPMO - IEMN

Silicon ring Magnets Flexible membrane Reflective coating Image from star distorted by atmosphere Image corrected by adaptive optics SmCo Ø 0.85 x 0.25 mm (COMADUR) 27/28

SLIDE 33

Energy harvesting (vibrations) : µ-generator (Univ. Hong Kong) Membrane pump for µ-fluidics (Suwon, Korea)

SLIDE 34

Bistable ultra-fast levitating µ-switch

1st fully integrated prototype Commutation 5 µm/30 µs/30 µJ/pulse

200 µm

fixed magnet fixed magnet moving magnet planar coil

Planar µ-turbo-generator

Voltages measured at 80,000 rpm Output ~ 1 W @ 100,000 rpm

Planar µ-motor

2 x 3 phases brushless 275,000 rpm on magnet / air bearings

MAGNETIC MICRO-ACTUATOR prototypes

Need for high quality integrated thick film magnets for MEMS !

Electrodep. Co85Pt15

µ-machined bulk NdFeB

Collab. G2ELab + CEA/LETI (Grenoble, France)

28/28

8 & 15 pole pairs

Ø 8 mm

SLIDE 35

Micro-magnets for MEMS

Candidate materials
Integration issues
Preparation of high performance materials

in thick film form by sputtering

Film patterning
Beyond magnets

Nora M. Dempsey Institut Néel, CNRS/UJF, Grenoble, France

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

1/28

SLIDE 36

High performance permanent magnet materials

840 200 4.9 1.00 CoPt 750 407 11.6 1.43 FePt L10 1173 333 6.4 1.30 Sm2Co17 1000 220 40 1.05 SmCo5 585 514 7.6 1.61 Nd2Fe14B RE-TM TC (K) (BH)max,th kJ/m3 µ HA (T) µ0MS (T) Material

µ0M B=µ0(H+M) H µ0Mr

MHc

(BH)max

↑(BH)max → ↓ magnet volume Mr ≤ MS Hc ≤ HA

Mr, Hc determined by microstructure 2/28

SLIDE 37

Routes to prepare thick film magnets

LEG / MISA

10 mm

5 x 5 µ m

Micro-machining

f bulk magnets

Screen printing Deformation (e.g. rolling) Sputtering Pulsed Laser Deposition (PLD) Electro-deposition Top-down routes Bottom-up routes

l L = 10xl 5 cm

CMSM Cincinnati LLN LETI

t = 5 µm l = 200 µm

Plasma spraying

3/28

SLIDE 38

Plasma spraying

LEG / MISA

10 mm

5 x 5 µ m

Micro-machining

f bulk magnets

Screen printing Deformation (e.g. rolling) Sputtering Pulsed Laser Deposition (PLD) Electro-deposition Top-down routes Bottom-up routes

l L = 10xl 5 cm

CMSM Cincinnati LLN LETI

t = 5 µm l = 200 µm

rolling : L10 alloys electro-deposition: L10 alloys

Material specific ! Routes to prepare thick film magnets

3/28

SLIDE 39

Micro-magnets for MEMS

Candidate materials
Integration issues
Preparation of high performance materials

in thick film form by sputtering

Film patterning

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

SLIDE 40

Influence of processing on magnetic properties

Sample degradation

e.g. drop in coercivity: µ-machining, screen printing

Dilution of magnetic phase → reduction of remanent magnetisation:

screen printing (vol. fraction of binder) plasma spray (porosity); NdFeB

T

Bulk 500 µm

k

µ-machined

Magnet texture : choice of process + process parameters

will determine ability to produce a textured magnet For now Isotropic : screen printing, plasma spraying, rolling…..

4/28

SLIDE 41

thickness lateral dimensions 1 µm 1 m 1 nm 1 µm 1 mm 1 mm

Magnet Dimensions

5/28

SLIDE 42

thickness lateral dimensions 1 µm 1 m 1 nm 1 µm 1 mm 1 mm

Individual magnet φ=8 mm; t = 500 µm

individual magnet

200 µm

Magnet Dimensions

5/28

SLIDE 43

thickness lateral dimensions 1 µm 1 m 1 nm 1 µm 1 mm 1 mm

Individual magnet φ=8 mm; t = 500 µm Magnet array 1x1 mm2; t = 100 µm

individual magnet / magnet array (batch fab.)

200 µm

Magnet Dimensions

Bi-stable µ-switch

LEG/LETI

Planar µ-motor

6/28

SLIDE 53

Integration issues for film magnets

Choice of substrate / buffer / capping layers:

will determine magnetic and mechanical properties, could influence cost of system must consider compatibility with - other µ-system components

microfabrication techniques
Film patterning

pre-patterned substrates deposition through masks post-deposition patterning

Thermal compatibility

for high anisotropy phases*, need elevated processing temperatures (Nd2Fe14B > 580°C, SmCo5 > 350°C, FePt > 450°C)

Wafer bonding allows full processing of magnet before integration of other

system components e.g. Si vs MgO *non-L10 Co80Pt20 may be produced by electro-deposition at low processing temp.

7/28

SLIDE 54

Integration issues for film magnets

Mechanical compatibility

will have a build up of stress in thick films mechanical stress ∝ difference in thermal expansion coefficients of susbstrate /buffer layer /magnetic layer Minimise strain : choice of substrate / buffer reduced surface area of magnet

NdFeB (50 µm) / Si

Chemical compatibility

pollution of - other system components

microtechnology equipment (clean room environment !!)

8/28

SLIDE 55

Micro-magnets for MEMS

Candidate materials
Integration issues
Preparation of high performance materials

in thick film form by sputtering

Film patterning
Beyond magnets

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

SLIDE 56

Triode sputtering machine

Base pressure : 10-6 mbar
Sputtering pressure : 10-3

mbar

Target ≤ 10x10 cm²
Deposition rate ≤ 20 µm/h
Substrate ≤ 100 mm

Tsub ≤ 750° C

Preparation of thick film magnets by sputtering

filament Anode Ar gas Substrate magnetic field Target

adapter for 200 mm substrates

2 10 4 5 5 t (µm) r(cm)

r

9/28

SLIDE 57

Film preparation parameters

Target:

Composition Target potential (kinetic energy of impinging ions)

Substrate:

distance to target (thickness+homogeneity) material (Si, Al2O3..) bias temperature during deposition

Deposition conditions

Ar pressure Film: composition µ-structure crystal structure crystal texture

Post-deposition annealing

10/28

SLIDE 58

{Si / Ta (100 nm) / NdFeB (5µm) / Ta (100 nm) } 2-step process: deposition at Tsub = X ° C + annealed in situ at 750° C for 10 min.

NdFeB thick films

influence of deposition temperature

Tsub=400° C

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5 µ0M (T) µ0Hi (T)

Tsub=500° C

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5 µ0M (T) µ0Hi (T)

Tsub=450° C

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5 µ0M (T) µ0Hi (T)

Tsub=300° C

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5 µ0M (T) µ0Hi (T)

ip Tsub = « Cold»

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5

µ0M (T) µ0Hi (T)

op

ip

op

(0 0 6)

Cross-section

Equiaxed grains Columnar grains

Grain size ↓ as Tsub ↑ => ↑ of the density of nucleation sites during deposition

11/28

SLIDE 59

have mechanical problems with continuous films….

n 100 mm wafer, central area (φ ≈ 3 cm) peels off when

film annealed Attributed to differential thermal expansion (NdFeB vs Si) + volume change during crystallisation

B.A. Kapitanov et al., J. Magn. Magn. Mater. 127, 289 (1993).

Mechanical issues

2

2 4 6 8 10 12 200 400 600 800

T, °C

∆

l / l

1

3

Si

Tcr

NdFeB Si

Tcryst

12/28

SLIDE 60

8
6
4
2

2 4 6 8

1,0
0,8
0,6
0,4
0,2

0,0 0,2 0,4 0,6 0,8 1,0

µ0M (T) µ0Hi (T)

op

ip

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5

µ0M (T) µ0Hi (T)

op
8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5

µ0M (T) µ0Hi (T)

op

ip

5µm 20µm 50µm

43µm

MEB MEB AFM rms=161nm

Mechanically intact thick NdFeB films

(deposit crystallised (Tdep = 550° C) + through mask)

Steel mask, φ = 5 mm

Surface roughness !!!

13/28

SLIDE 61

8
6
4
2

2 4 6 8 T

sub = 350°

C ip

op

M (a.u.) µ

0H (T)

Tsub = 350° C

8
6
4
2

2 4 6 8 T

sub = 400°

C ip

op

M (a.u.) µ

0H (T)

Tsub = 400° C

8
6
4
2

2 4 6 8 T

sub = 500°

C ip

op

M (a.u.) µ0H (T)

Tsub = 500° C

8
6
4
2

2 4 6 8 Tsub = 300° C ip M (a.u.) µ

0H (T)

Tsub = 300° C For Tsub = 350-400° C µ0Mr ≈ 0.8 T

SmCo thick films

infleunce of deposition temperature

40 60 80 3000 6000

2 2 2 1 1 1 2

Th2Zn17

500° C 400° C 350° C Cold dep 300° C

Cr 2 1 1 1 2 1 1 1 4 3 2 1 4 1 1

TbCu7

Si

200 300 400 500 600 0,0 0,5 1,0 1,5

µ0Hc (T) Tdep (° C)

14/28

SLIDE 62

Thick hard magnetic films (5 µm) on Si

8
6
4
2

2 4 6 8 T

sub = 350°

C ip

op

M (a.u.) µ

0H (T)

8
6
4
2

2 4 6 8

1,5
1,0
0,5

0,0 0,5 1,0 1,5 µ0M (T) µ0Hi (T)

op

ip

(BH)max=400 kJ/m3

(006)

Tdep: 450° C + T ann : 750° C

r Tdep = 550°

C Tdep: 350° C Tdep: ≥ 400° C

4
3
2
1

1 2 3 4 "cold" 400° C 500° C 600° C M (a.u.) µ0H(T)

NdFeB

ut-of-plane texture

SmCo in-plane texture FePt isotropic

(200)

op

ip

(BH)max=140 kJ/m3 µ0Hc > 1 T Corrosion resistive 15/28

SLIDE 63

Micro-magnets for MEMS

Candidate materials
Integration issues
Preparation of high performance materials

in thick film form by sputtering

Film patterning
Beyond magnets

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

SLIDE 64

Micro-structured Magnets

2002 Budde JMMM242_1146

sacrificial Cu mask SmCo Si substrate SmCo Sputtered SmCo Lift-off of Cu mask by wet etch Electro-deposited

2002 Zana_JAP_91_7320 2 µm Co80Pt20 pillars

PLD of FePt (L10) Local laser annealing → disordering

40 µm 2006 J. Buschbeck_JAP (IFW)

Sputtering of amorphous NdFeB Local laser annealing → crystallisation

2003 Okuda_JJAP_42_6859 2005 Rhen_JAP_97_113908

Electro-deposited Co50Pt50

in nanoporous membranes 450 µm pole pitch µ0Hc= 0.4 T, (BH)max= 34 kJ/m3 µ0Hc= 1.3 T

Film thickness 40 nm 16/28

SLIDE 65

Proposed routes for the structuration of magnetic films

2) Magnetic 1) Topographic

M mask H

Deposition on prepatterned subst.

Heat

Etching of magnetic layer + polishing

Thermomagnetic patterning irreversible reversible

cf: thermomagnetic writing for recording media

17/28

SLIDE 66

cf: thermomagnetic writing for recording media 2) Magnetic 1) Topographic

M mask H

Deposition on prepatterned subst.

Heat

Etching of magnetic layer + polishing

Thermomagnetic patterning irreversible reversible

Proposed routes for the structuration of magnetic films

SLIDE 67

Topographically patterned films

Use of pre-patterned Si/SiO2 substrate with sets of trenches of different lateral dimensions « cold » deposition of Ta(100nm) / NdFeB (5 µm) /Ta (100 nm) + in-situ anneal (750° C/10 min)

Si

SiO2 x y

10 µm in-plane loop of a piece containing 3 sets of trenches (widths 5, 10 and 20 µm)

0.06
0.04
0.02

0.02 0.04 0.06

8
6
4
2

2 4 6 8 M (a.u.) µ

0H(T)

Need local magnetic characterisation !

18/28

SLIDE 68

Trench filling on pre-patterned wafers

10µm 10µm 10µm 10µm NdFeB SmCo 2µm

19/28

SLIDE 69

Local magnetic characterisation for MEMS

Need to measure stray fields produced by µ-magnets :

to characterise inhomogeneities

(process optimisation)

to calculate forces at work in the µ-system

(simulation/design optimisation) Tools : Scanning Hall probes (sensititvity + scan param. adapted to MEMS) Kerr microscope + MOIF

20/28

SLIDE 70

MOIF* imaging of topographically patterned films

Magneto Optic Imaging Film

(e.g. ferrite garnet) uniaxial MOIF Bz distribution reconstructed from halftone planar MOIF images at a distance of 4 µm sample saturated

ut-of-plane

Theoretically calculated Bz/Br at 1, 2, 4 and 8 µm from film surface (tfilm = 3.5 µm, p = 20 µm h = 10 µm l = 100 µm)

multipole unidirectional

MOIF

Tver State University (Russia)

21/28

SLIDE 71

Wet etching/planarisation of RE-TM films

NdFeB SmCo Hystersis loops

f wet etched /planarised

and annealed NdFeB

Films etched in amorphous state

#1: capped with Ta + annealed #2: ion etched + capped with Ta + annealed #3: annealed

Si RE-TM

lateral over-etching ≈ 15 µm

Wet etching

4
2

2 4

1,0
0,5

0,0 0,5 1,0

M/M4T µ0H (T)

covered with Ta ion etching + covered with T not covered

# 1 # 2 # 3 22/28

SLIDE 72

2) Magnetic 1) Topographic

Deposition on prepatterned subst.

M mask H Heat

Etching of magnetic layer + polishing

Thermomagnetic patterning irreversible reversible

Proposed routes for the structuration of films

cf: thermomagnetic writing for recording media

SLIDE 73

Thermo-Magnetic patterning

f NdFeB films

Film surface Uniaxial MOIF

Demonstrates the perspective for optical interference thermomagnetic writing

planar MOIF

Magnetisation modulation due to Fresnel diffraction at mask Pitch (~12 µ µ µ µm) determined by λ λ λ λlaser and distance from mask to sample.

mask Hext Pulsed laser NdFeB Hc > Hext

23/28

SLIDE 74

Applications of µ-magnets

y x z y x z

Collaboration: G2ELab : µ-system designer LETI : µ-fab platform Institut Néel : magnet films Alcatel Space : end user Funding: ANR “Nanomag2“ Contactless containment of 3µm latex microbeads with linear magnetic traps LEG and CEA (Biochips Laboratory, SMOC/LETI)

RF µ-switches Diamagnetic levitation

H. Chetouani et al., Transducers ‘07

58 process steps (including 9 litho.) « clip » C. Pigot

24/28

SLIDE 75

Micro-magnets for MEMS

Candidate materials
Integration issues
Preparation of high performance materials

in thick film form by sputtering

Film patterning
Beyond magnets

ESM2007 - September 9-18th 2007, Cluj-Napoca, Romania

SLIDE 76

Beyond hard magnets: switchable materials

Switchable magnetic materials:

Reversible change of magnetic properties (MS, HA) by an external parameter.

Why go beyond hard magnets?

They are driven by currents in coils ⇒ Joule heating losses ⇒ Complex design

Thermo-switchable

New functionality (e.g. laterally resolved modifications by controlled laser heating) Contactless !

E-field switchable

Novel concept Unexplored potential e.g. FePt, FeRh

Strain switchable

Magnetostrictive Multiferroics magnetic shape memory 25/28

SLIDE 77

Thermo-switchable materials

35 70 105 140 290 300 310 320 330

Fe48Rh52

M (emu/g) T(K)

3
2
1

1 2 3

300 320 340 360 380 M(T) at 2mT M(emu/g) T(K) Tcomp = 335 K GdCo

3Cu2

Antiferro ferro

n / off switching

Ferrimagnetic Compensation up / down switching In-plane out-of-plane 90°switching GdCo3Cu2 e.g. FeRh NdCo5

26/28

SLIDE 78

E-field switchable materials

Surface effect: High surface-to-volume ratio needed Prospect for NEMS

nanoporous

Selective dissolution of sacrificial component

Compaction
Sintering

Nanocrystalline powder nanoporous Alloy film

M E>0 E=0

FeRh

T E=0 E>0 H MS

FePt

1 2 0 0
1 0 0 0
8 0 0
6 0 0
4 0 0
4
2

2 F e P t F e P d 4 n m 2 n m 4 n m 2 n m

δ Coercivity / %

F e P t p o te n tia l v s . P t / m V

reversible modification of magnetic properties in itinerant electron systems

FePd FePt

+

~ 1 nm

+

+
+
+
U

Electrolyte 27/28

SLIDE 79

Other Magnetic Materials for MEMS

Magnetostrictive

bimorph membranes (µ-pump)

Planar micropump

TbFe2 (λ > 0) Si (λ = 0) SmFe2 (λ < 0)

Magnetic Shape Memory Alloy

See K. Dörr (talk) + M. Thomas (poster)

28/28

SLIDE 80

Institut Néel :

A. Walther (PhD), C. N’dao (PhD) and D. Givord

G2Elab :

O. Cugat, J. Delamare, G. Reyne and H. Chetouani (PhD)

LETI/CEA

C. Marcoux, B. Desloges, C. Dieppedale

TVER STATE UNIVERSITY

R. Grechishkin, M. Kustov (PhD)

Acknowledgments

WEB: Bernard Legrand (IEMN) « Ecole Nanosciences et Nanotech. – Autrans 2006 » http://www.mems-exchange.org http://www.memx.com

SLIDE 81

SLIDE 82

SLIDE 83

Applications of THERMO-REVERSIBLE Permanent Magnet

GdCo3Cu2 ( Tcomp is 90 oC)

Grechishkin et al. APL 89, 122505 (2006); D. Mavrudieva et al, SENSOR LETTERS 5, 1 (2007)

thermally controlled Actuator: remotely interrogated temperature sensor : no bias

signal element square loop soft magnetic tape (nc Fe81B13.5Si3.5C2) producing detectable harmonics. Bias with magnet → appearance of even harmonics

fixed magnet suspended TR magnet

indicates direction of TM magnet suspended TR magnet rotates by 180° when heated above Tcomp