rf-mems technology: progress status and commercial outlook · high m etal s tre ss a nd hi gh...

F. COCCETTI CNRS-LAAS / Fialab - [email protected] 1Microwave & RF 2013

RF-MEMS Technology: Progress Status

and Commercial Outlook

Technologie MEMSRF: état d'avancement et

commercialisation

Fabio COCCETTIFialab / LAAS-CNRS

Toulouse

10 & 11 avril 2013

Paris Expo - Porte de Versailles

Le salon des radiofréquences, des hyperfréquences,

du wireless et de la fibre optique


LAAS at Glance:

µ/N Systems TechnologyRF-MEMS @ LAAS (2000 – present)

15 PhD Thesis

7 Post-Docs

Funding Agencies:

ANR, EC (FP6), DGA, Region MP

Main Partnerships:

Fialab - ThalesAleniaSpace – CNES -

LETI – IHP - …


Fialab at Glance:REBRANDING

NOVA MEMS became FIALAB starting from January 1st 2013

��

Tests and analyses laboratory.

Our first excellence field is

MEMS/Microsystems

��Enlarging business BEHOND

MEMS

to major industrial markets:

Embedded systems and

Mechanical Parts.


Outline

• RF-MEMS technology progress status at glance

• R&D Methodologies and Achievements

• Conclusions and Perspectives


Technology Maturity and Adoption

Gartner Hype cycle

Source: Gartner Research (1995)


20111st commercial

consumer

electronics RF-

MEMS1995-98RF-MEMS goes

viral in R&D

environment

Source: Based upon WTC’s (2008) (now IHS – iSuppli )


Gartner Hype cycle for « RF-MEMS Technology »


20111st commercial

consumer

electronics RF-

MEMS1995-8RF-MEMS goes

viral in R&D

environment

Source: Based upon WTC’s (2008) (now IHS – iSuppli )


Gartner Hype cycle for « RF-MEMS Technology »

Bulck Micromachining

(K. Granier et al. 2000)IN

OUT

IN

OUT

High Power RF MEMES

(D. Dubuc et al.2003)Mm-wave MEMS

(V. Puyal et al. 2009)Switch Ohmic (RS)

(P. Pons et al 2010)


Source: Slocum, M.S., ‘Technology Maturity Using S-curve Descriptors', TRIZ Journal, April 1999


S-Curve

> 1 Billion USD

> 1 Million USD


Commercial RF -MEMS Components

Source: Radant MEMS switch

Source: Wispry MEMS tunable digital capacitor


Timeline of MEMS devices

Source: R. Grace Associates (2012)

Year

19

54

19

55

19

56

19

57

19

58

19

59

19

60

19

61

19

62

19

63

19

64

19

65

19

66

19

67

19

68

19

69

19

70

19

71

19

72

19

73

19

74

19

75

19

76

19

77

19

78

19

79

19

80

19

81

19

82

19

83

19

84

19

85

19

86

19

87

19

88

19

89

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00

20

01

20

02

20

03

20

04

20

05

20

06

20

07

20

08

20

09

20

10

20

11

20

12

20

13

Product

Pressure Sensors 36

Accelerometers 20

Nozzles 24

Photonics/Displays 25

Bio/Chemical Sensors 25

Radio Frequency (R.F.) 12

Gyros/Rate Sensors 22

Micro Relays 27 34

Legend: Discovery Product Evolution Cost Reduction Full Commercialization Elapsed Time in Years


Timeline for MEMS devices Commercialization

Product DiscoveryProduct

EvolutionCost

ReductionFull

CommercializationDiscovery to Commercialization

Pressure Sensors 1954-1960 1960-1975 1975-1990 1990 36

Accelerometers 1974-1985 1985-1990 1990-1998 1998 20

Nozzles 1972-1984 1984-1990 1990-1996 1996 24

Photonics/Displays 1980-1986 1986-1998 1998-2005 2005 25

Bio/Chemical Sensors 1980-1994 1994-2000 2000-2005 2005 25

Radio Frequency (R.F.) 1994-1998 1998-2002 2002-2006 2006 12

Gyros/Rate Sensors 1982-1990 1990-1996 1996-2004 2004 22

Micro Relays 1977-1982 1993-1998 1998-2004 2004-2011 27-34

Source: R. Grace Associates (2012)


Failure mechanism Failure defect Failure mode Failu re cause

1 Dielectric charging of the insulator

Non-permanent stiction -Drift in C-V, Vpi, Vpo -Dead device

2. Electric field charge 3. Radiation 4. Air-gap breakdown 5. Electron emission

2 T-induced elastic deformation of the bridge

Non-permanent deformation of the bridge (restored when T-source is removed), possibly stiction

-Drift in C-V, Vpi, Vpo -Dead device

1. Environment T 2. Different CTE 3. Power RF signal induced T 4. Non uniform T

3 Plastic deformation of the bridge Permanent deformation, possibly stiction -Drift in C-V, Vpi, Vpo -Dead device

1. Creep 2. Thermal induced charges in

material properties (for T > Tc)

4 Structural Short (electrical and non-electrical connections)

Particles, shorted metals, contamination, remains of sacrificial layer, stuck bridge

Anomalous or dead device

- Contamination, particles, remaining sacrificial layer

- Wear particles - Fracture - Lorenz forces - Shock

5 Capillary Forces Stiction Dead device Humidity (Package leaks)

6 Fusing Opens, roughness increase Dead device High RF power pulses, ESD

7 Fracture Broken bridges or hinges Dead device • Fatigue • Brittle materials and shock • High local stresses and shock

8 Dielectric breakdown Dead device, possibly stiction Short between the bridge and the actuation electrodes

• ESD • Excessive charging of the

insulator

9 Corrosion Dendrites formation, oxidation, changes in color

-Drift in Rc C-V, Vpi, Vpo -Dead device

• Humidity, enhanced by bias • Corrosive gases induced

chemical reaction (ex. oxidation)

10 Wear, Friction, Fretting corrosion

Surface modifications, debris, stiction -Drift in Rc C-V, Vpi, Vpo -Dead device

Rough Surfaces in sliding contact

11 Creep Deformation of the bridge in time -Drift in C-V, Vpi, Vpo -Dead device

High metal stress and high temperature, creep sensitive

12 Equivalent DC voltage Self biasing stiction -Drift in C-V, Vpi, Vpo -Dead device

High RF power including spontaneous collapsing or stiction of mobile part

13 Lorenz forces Self biasing stiction Anomalous switching behavior

• High RF power in two adjacent lines

• External magnetic field

14 Whisker formation Bumps in metal, holes in insulator on top of metal layers, etc

Anomalous down capacitance

High compressive stress in metal resulting in grains extrusions, might be enhanced

15 Fatigue Broken bridges and hinges, cracks, microcracks

Shifts in electrical and mechanical properties

• Large local stress variations due to motion of parts

• Enhanced probability of cracks

16 Electromigration Cracks, opens, thickness changes in metal lines

Increase of resistance, opens, shorts

High current density

17 Van der Waals forces Stiction Dead device Smooth and flat surfaces in close contact

18 Electric field-induced meniscus Stiction Anomalous or dead device

Residual layer of water (due to residual RH)

Failure Mode Effect Analysis (FMEA) Application Based

- Movable Thin membranes

- Metal-to-Metal Contact

- Dielectric-to-Metal Contact


Major Failures in MEMS Switches

Charging effect

Contact degradationMaterial transfers

Radant MEMS sealing ring

Packaging hermeticity

Decohesion of grain boundaries

Fatigue & creep of movable parts

cantilever

packaging

Source: A. Broue PhD (LAAS-Fialab - 2012)


Major Challenges / Limitations

� Dielectric charging in electrostatic actuated devices

� Metal contact degradation (welding, wearing,

contamination,…): in resistive switches

� Thermal induced elasto-plastic phenomena (creep-

fatigue): in membrane under high workload


Metal-to -Dielectric contact physics

Build up Surface potential

Source: U. Zaghloul PhD (CNRS-LAAS – 2011) - Grant from: RTRA – EDA –Région MP


C-V Time zeroC-V after 19 hours

Actuation signal builds up charge in the dielctric resulting in a

SHIFT of the C-V Characteristic

Good Source: EC FP6 (AMICOM 2004-2007)

Dielectric Charging in Capacitive Switches:

Shift of the Vpi/Vpo

Failed


Charge injection (through asperities)AFM based investigation techniques

Actuated MEMS

MEMS Bridge

Gold coplanar strips (underpath)

Dielectric layer

Substrate

The AFM is the most suitable tool to simulate

the “local” charge injection process in

electrostatically actuated MEMS

Roughness of electroplated Au

AFM equipment

V



Surface potential Decay Surface potential distribution

tpUp

V

Charge injection

KPFM Methodology in TWO steps

FIRST step: Charge injection

AFM based techniques: Kelving Probe Force Microscopy Charge/discharge kinetic

3

2LSH

Surface potential scanning

1

SECOND step: Surface potential scanning

Space

Tim

e

Su

rface

Po

ten

tial

( )

−⋅∆=∆β

τt

CtC exp0

Array of single point

charge injection



AFM based techniques:Material Evaluation: Silicon Nitride

−=β

τt

UtU s exp)( 0

M. Lamhamdi, et al. J.

Microelectron. Reliab. 46,

(2006)

Surface (Built-in) potential

KPFM

Discharging time-constant

SiNx (HF Type) vs SiNx (LF Type)

U. Zaghloul et al., Nanotechnology 22, 205708, 2011


AFM based techniques: Force Distance CurveCharge discharge kinetics PLUS adhesive force

Source: V. Shahin et al. JCS 2005

U. Zaghloul et al., J. Colloid Interface Sci. 358, 2011


AFM based techniques: Force Distance CurveEffect of RH and applied bias on Adhesive force

RH combined with applied bias yield higher adhesion forces due

to electrostatic induce meniscus phenomena.



FDC on MEMS


SO

UR

CE

: M

EM

S f

rom

AM

ICO

M N

OE

20

07


Environmental (PACKAGING) conditions:Contaminants on Charge accumulation : surface potential and

relaxation time

Contaminants as C and/or O yields higher surface potential

(charge accumulation) and slower discharging (larger decay time

constants)

U. Zaghloul et al., Nanotechnology 22, 035705, 2011


Metal-to -Metal contact physics

Source: A. Broue PhD (LAAS-Fialab - 2012) Grant from: ANR – EDA/DGA – Region MP.


Micro-contact reliabilityFailure mechanisms

Commonly reported failure mechanisms are:

• Mechanical (cold welding, strain hardening, wear, fretting…)

• Electro-thermal (hot welding, annealing, arcing, creep, softening…)

• Chemical (contaminations, frictional polymers, corrosion, oxidation or sulfidation: formation of insulating films at the extreme surface)

These Mechanisms yield topological, mechanical and/or electricalproperties modifications at the contact



Micro-contact physics

• The contact resistance Rc is linked to the constriction of current lines

between both contacts � local increase of the current density +

ballistic transport of electrons

Relationship between contact resistance Rc and the load applied Fc on the contact

The highest contact spot temperature Tc expressed as a function of the contact voltage Vc

RC = AFC−x

04

2

TL

VT c

c +=

Electrical contact area

RContact = Γ(K )RHolm + RSharvin +RFilm ?( ) RSharvin = 4ρK3π a

RHolm = ρ2a

where and

The effective contact

area is much smaller

than the apparent one

� due to the small force

available in micro

actuators (50 – 250 μN)

Diffusive

conduction

mode

Ballistic

conduction

mode

Source: A. Broue PhD (LAAS-Fialab – 2012)

Grant from: ANR – EDA/DGA – Region MP.


Test vehicle description

Au-to-Au Ru-to-Ru Au-to-Ru

++ High bulk conductivity

++ High oxidation resistance

- - Soft material (large modification of

the contact surface, susceptible to

contact wear and stiction)

Au ++ Higher hardness

++ Higher melting temperature

- - Lower bulk conductivity

Ru

Monometallic contacts

Contact materials Au Ru Rh Ni

Electrical conductivity (mΩ-1.mm-2) 45.7 14.9 21,1 14,3

Softening temperature (°C) ~100°C ~430°C x ~520°C

Melting temperature (°C) 1063°C 2450°C 1964°C 1453°C

Boiling temperature (°C) 2966°C 4900°C 3695°C 2837°C

Estimated hardness (GPa) ~1.6 ~10.1 ~25 ~13,7

Rh

Ni

Rh-to-Rh Au-to-Ni

Bimetallic contacts


Source: A. Broue PhD (LAAS-Fialab – 2012)



Description of the experimental set-up

• Specific contact investigation:Source Modes Switching Modes

•Current source or voltage source

Hot switching

Cold switching

Mechanical switching

Input Parameters Range

•Current level (Ic) 10-5 to 1A

•Maximum load applied (Lmax) 1µN to 6mN

•Contact voltage(Uc) 10-5 to 40V

•Holding plateau at load max thold 0 to several min

Environment Dry nitrogen (< 5% RH)

Outputs

•Voltage Drop (Vc) or current drop

(Ic) [depending on the source

mode]

•Contact stiffness (K)

•Tip Displacement (d) •Contact resistance (Rc)

*Contact force resolution = 1µN

displacement resolution = 1nm

*test structures are reported and micro

bonded on a PCB (Printed Circuit Board).


Test Vehicle (4 point)



Contact Characterization

Contact resistance versus contact force at different values of current

A. Broue, et al. IEEE Holm Conference on Electrical Contacts, Charleston (USA), 2010

Au/Au

Rc

R2

F1 Force de contact F2

R1

Couple de matériaux



Metal Contact Characterization

Contact resistance versus contact force at different values of current

A. Broue, Iet al. MEMS 2010, Hong Kong (Chine), 24-28 Janvier 2010



Metal Contact Characterization

Major failure modes for different metal type vs cycling

Source: F. Ke, et al. Microelectromechanical Systems, Journal of, 2008






� Thermaly induced elasto-plastic phenomena (creep-

fatigue, …): in membrane under high workload


Free Standing Membrane Physics

Source: Innovation For High Performance

Microelectronics (IHP 2012)


Thin Membrane Physics

– Co-integration CMOS-MEMS Based on

commercial BiCMOS process

– RF behaviour strongly dependent from

membrane shape in the contact area

Contact Region

UP

stat

eD

OW

Nst

ate

MIM

MIM

Resistive contact (TiN-TiN)

Source: Innovation For High Performance Microelectronics (IHP 2012)


High TRL environments• Low dispersion

– 6 different versions of the switch are compared

0 10 20 30 40 50 60 70 80 90 100 110 120-25

-20

-15

-10

-5

0

Isol

atio

n (

dB)

Frequency (GHz)

V2 V3 V4 V5 V6

0 10 20 30 40 50 60 70 80 90 100 110 120-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0R

L (d

B)

Frequency (GHz)

V2 V3 V4 V5 V6

0 10 20 30 40 50 60 70 80 90 100 110 120-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

IL (

dB)

Frequency (GHz)

V2 V3 V4 V5 V6

Design and characterization done in IHP

All the switches have the same contact area and inductors are added on the anchors for

frequency tuning

Grant from: ESA – IHP – ThalesAleniaSpace

Source: N. Torres Matabosch PhD 2013 (CNRS-LAAS –ThalesAleniaSpace)


Effect of Process Dispersion • Fabrication process dispersion

� UP and DOWN capacitance dispersion due to different stress level over the wafer

CMIM

ZMEMS

CM1-M3

Lelectrode

Relectrode

Ranchor

Lanchor

Lbeam

Cox2

Cox1

IN OUTSubstrate

coupling model

16 18 20 22 24 115120125130135140145150

0

2

4

6

8

10

Nu

mb

er

of

de

vic

es

CMEMS(fF)

UP state σUP=1.2fF

DOWN state σDOWN=6.3fF

Precision Impedance

Analyzer 4294A

(@1MHz)

CDOWNCUP


Source: N. Torres Matabosch PhD 2013 (CNRS-LAAS – TAS)


• Failure anlaysis– S-Parameters before and after stress

• The resonance is due to the mechanical fatigue of the membrane– UP state: CMEMS and CM1-M3 increase– DOWN state: resistive contact membrane-electrode � not possible to

model

25 30 35 40 45 50 55 60 65 70-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

IL (

dB

)

Frequency (GHz)

16h 1h Initial

20 25 30 35 40 45 50 55 60 65 70-7

-6

-5

-4

-3

-2

-1

0

IL (

dB)

Frequency (GHz)

Model Initial After stress

Working device Failed device

d(M1-M3) d(M2-M3)

Effect of Process Dispersion

Grant from: ESA – IHP – ThalesAleniaSpaceSource: N. Torres Matabosch PhD 2013 (CNRS-LAAS –TAS)


• Failure analysis– Test plan: 1h constant DC stress

• Industrial requirements (TAS): ∆∆∆∆Vp<10% and ∆∆∆∆IL<1dB

Vpout >36V and |Vpin -Vpout |<1V

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%

100%

21 23 25 27 29 31 33 35 37 39

Dev

iatio

n in

VP

OU

T

VPOUT (V)

Devices that succeeded the tests

Define a failure criteria for wafer screening

Tests done in ThalesAleniaSpace facilities - Toulouse

The diameter of the circles represents the |Vpin -Vpout |

Effect of Process DispersionFailure criteria and identification

T = 22°CRH = 45% (rel. humidity)


Source: N. Torres Matabosch PhD 2013 (CNRS-LAAS –TAS)


• Early detection of failed devices– Profilometer-based Measurements � Real time and Non Intrusive– Allow rapid wafer level monitoring (screening)

5 6 7

13

14

15

16

X

Y

Effect of Process Dispersion

180 190 200 210 220 230 240 250 260 2700,0

0,5

1,0

1,5

2,0

2,5

3,0

d(M

2-M

3)

Y (um)

Failed Succeeded

4.7µm

2.8µm

0 50 100 150 200 250 3000123456789

10111213

d(M

1-M

3)

X (um)

Failed Succeeded

Grant from: ESA – IHP – ThalesAleniaSpaceSource: N. Torres Matabosch PhD 2013 (CNRS-LAAS – TAS)


Conclusions & Perspectives

MEMS switches failure mechanisms are a difficult multiphysics / multidisplinar challenge. Their study by means of “ad-hoc” experimental methodologies such to target phenomena separately, has allowed to advance in the fundamental understanding of the underlying phenomena.

In commercial devices solutions to prevent major FM include:

� Metal-to-Dielectric Charging*: � No contact actuators (dielectricless); � Small CON/COFF ratio

� Material engineering (enhance discharging mechanisms) � Higher Process complexity

� Metal-to-Metal Contact Degradation*:� Hard metals � Lower contact resistance, Higher Process complexity

� Strong forces � Higher actuation bias

� Movable Membrane/Beams Creep and Fatigue:� Thermal stress engineering/compensation � Higher process complexity

� Thicker membranes � Higher actuation bias

* Working environment (e.g. packaging) is essential: inert gasses with low RH contents and low contaminants (hermetic)



Maturity and Adoption

� CMOS platform are the most suitable solution for consumer mobile electronics

(co-integration of analog and digital electronics/fuctionalities)

� MEMS foundries well suited for pick-and-replace solution (Yet for

niche/smaller market)

� R&D MEMS foundries essential for supporting both (proof of concept and

failure analysis)

R&D OUTLOOK

� New materials and processes (Carbon based) for faster and smaller

MST (NEMS, i.e. mass sensors or SW)

� Advanced physics (e.g. tribology): electric and thermal transport

across atomic scale multiasperity contact;



R&D OUTLOOK

� New materials (Carbon based) for faster and smaller MST (NEMS, i.e.

mass sensors or SW)

� surface physics tribology: electric and thermal transport across

atomic scale multiasperity contact;

Source: IBM Reserach Zurich (2013)


Fostering Education on RF-MSThttp://educ.laas.fr/ISS_RFMEMS2013

rf-mems technology: progress status and commercial outlook · high m etal s tre ss a nd hi gh...

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