current r&d challenges of the mobile mems market · | 4 •mostly based on si-based mems with...

MEMS Engineer Forum 2017 | April 26, 2017Dr Julien Arcamone, CEA-Leti’s MEMS Business Development Manager ([email protected])

Current R&D challenges of the mobile MEMS market

and how CEA-Leti is facing them

mailto:[email protected]

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• Mobile devices, in particular smartphones, are a pillar of IoT

• MEMS-related innovations & trends in smartphones:4 focuses in this presentation

Current MEMS innovations for IoT and mobile devices

MEMS Engineer Forum 2017 J. Arcamone CEA-Leti

Towards smaller, cheaper, and higher performance“traditional” MEMSAccel. – Gyros – Pressure

Towards high-SNR

Microphones

More and more BAW resonators/filters

Towards new user-interfaces (haptics)

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Outline

Pushing the limits of Si-based MEMS with M&NEMS technology

Piezoelectric MEMS for enhanced performance and new functions


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• Mostly based on Si-based MEMS with capacitive detection

• (Technical) challenges: reducing cost and size while maintaining or enhancing performance

• Extreme miniaturization is incompatible with capacitive detection because of SNR degradation (unfavorable scaling laws)

Challenges of “Traditional” MEMS (Accel. – Gyros – Pressure)

for usage in smartphones


MEMS

NEMS

CEA-Leti proposes of a new detection paradigm to overcome this limitation: M&NEMS (double thickness) piezoresistive technology

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• Si nanobeams-based Piezoresistive Detection

• Generic process, transduction and readout electronics

• Miniaturization, cost-effective and low-power

• First industrial transfer to Tronics (9-axis)

A disruptive Si-based generic platform for sensor fusion(protected by more than 20 Leti patents)

3-axis Accelerometer 3-axis Magnetometer3-axis Gyroscope Pressure sensor(Absolute & differential)

Microphone

Under development

6-axis A+MMech. footprint 1.1mm²

Pressure sensorMech. footprint 0.12mm²


Leti’s M&NEMS multi-sensor technology

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How does it work?Example of Y accelerometer in top view


FMEMS thickness

(10-20µm)

NEMS thickness (250-500nm)

R

R

Gauge 1

Gauge 2 Inertial mass

| 7MEMS Engineer Forum 2017 J. Arcamone CEA-Leti

How does it work?Example of Y accelerometer in top view

MEMS thickness (10-20µm)

NEMS thickness (250-500nm)

R-R

R+R

Tensile stress(Fg/A)

Compressive stress(-Fg/A)

• Major benefits of piezoresistive detection with Si nanobeams• Mechanical amplification (lever effect): Fg 30 F• Stress amplification by leveraging scaling laws

(force applied on ultra-small cross-section A of nanobeams)• High sensitivity and linearity

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• Reliability: are Si nanobeams fragile?• Gauges withstand more than 1GPa (Si value) use of mechanical stops

limiting the motion to equivalent maximum stress of 300MPa• Demonstrated shock resistance up to 10 000g

• Core process with SOI wafer and epitaxy• Ongoing developments to lower the cost by getting rid of SOI and/or epitaxy

• Stability considerations: TCO and TCS comply with automotive and consumer specs (experimentally demonstrated)

Maturation of M&NEMS technology


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• Bias instability= 1.4°/hr

• Device area: 0.36 mm²

• Open-loop detection

• Q-factor: 3 000 (4 mbar WLP)

Last progress on M&NEMS gyroscope


Bias ARW = 0.06°/hr(for I=550µA)

Bias instability = 1.4°/hr(no temp. control)

Device area: 800μm x 450μm

Root Allan Variance vs. bridge current

• Possible further improvements by

• Lowering package pressure (4 <1mBar)• Increasing MEMS thickness (20 60µm)

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Outline

Pushing the limits of Si-based MEMS with M&NEMS technology

Piezoelectric MEMS for enhanced performance and new functions


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Piezoelectric (PZE) MEMS provide enhanced performance and/or open new functions


Towards high-SNRMicrophones

More and more BAW resonators/filters

Towards new user-interfaces (haptics)

• Leti has a more than 10 years background on PZT and AlN-based devices, and their process integration on 200mm wafers

• Leti’s pioneering activity on emerging materials such as LNO or electro-active polymers

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• Haptics: interacting with the environment by the sense of touch

• Many applications can be enabled by novel interfaces based on haptics feedback

Piezoelectric MEMS actuators for haptics devices


New way to purchase online Smartphones & tablets: new ways to interact

PZE Actu

ators

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• Existing haptic solutions:

• Eccentric rotating mass (ERM), “bulk” piezo-ceramic, electrostatics… Limited feedback effect and high power consumption

• Squeeze-film effect on a plate

• Based on Lamb waves in a plate resonator produced by thin-film actuators (Displacement amplitude > ±1µm) creation of a thin air layer between plate and finger Overpressure that tries to lift the finger

Haptics feedback based on squeeze-film effect


Plate resonator

Thin air layer

The friction coefficient is therefore modulated depending

on the finger position: kind of “air lubrication”

PZE Actu

ators

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• Leveraging bimorph effect

• Structural PZE material, PZT for instance

• DC bias• PZT contraction (d31, e31)• Membrane or plate bending

depending on mechanical conditions


PZE Actu

ators

Structural material

Bottom electrode

Piezoelectric material

Top electrode

Clamp

Clamp

V

V

How to actuate the plate?

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• Modal analysis (FEM simulations with Coventor):

• Unclamped 60×40 mm² silicon plate (725µm thick)• Piezoelectric material parameters: d31=150pm/V• Identifying maximum substrate displacement amplitude areas• Matching thin-film PZT actuators position with max substrate

displacement amplitude areas


PZE Actu

ators

Proof-of-concept on a Si plateModal analysis for actuator design

Actuatorcolumns


Proof-of-concept fabrication

• Based on Leti’s 200mm PZT MEMS technology (transferred to two major foundries including STMicro)

• Substrate sawing to transfer individual plate onto a carrier

PZE Actu

ators

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Characterization and post-simulation

• Laser vibrometer measurements versus simulations

• Actuation with VDC=12V +VAC – peak to peak

• Frequency 35kHz• Measured substrate displacement amplitude in good agreement with

simulation: 1.1µm @8V

PZE Actu

ators

• Haptic feedback effect was felt with the finger


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Conclusion and perspectiveson haptics devices

• Thin-film PZT actuators enable µm-range substrate displacement amplitude (with Lamb waves) required for haptics applications

• Predictive FEM model fits well with measurements

• Haptic feedback effect felt with the finger: proof-of-concept on Si substrate and PZT actuators

• Ongoing works:

PZE Actu

ators

• AlN actuators for integration on glass

• Actuators based on printed electro-active polymers


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• A key element for RF front-end modules for telecom band selection (band-pass filter)

• More than 20 BAW filters dies in iPhone 6S

• Even higher number (>100) in future 5G devices

RF piezoelectric MEMS: BAW resonators / filters


PZE RF d

evices

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• BAW band-pass filters are based on ladder filters comprising several resonators

• One ladder filter cell contains two BAW resonators whose coupling coefficient kt²

(defined as 𝑓0−𝑓𝑎𝑛𝑡𝑖𝑟𝑒𝑠𝑜𝑛𝑎𝑛𝑐𝑒𝑓0

) is critical in terms

of filter bandwidth and insertion loss

• All BAW resonators are based on AlNwhose kt² is 6.5%

BAW resonators / filters


PZE RF d

evices

A. Reinhardt et al., «BAW technology for advanced RF architectures» Workshop WSE – 2009 International Microwave Symposium

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BAW resonators / filters trend: “Improving” AlN or replacing it


PZE RF d

evices

• RF front-end modules would benefit much from increased frequency agility:

• Tunability of center frequency and bandwidth• Higher bandwidth

• This “agility” is directly linked to the kt² coefficient of AlN

• Increasing the kt² is possible by

• Doping AlN, for example with scandium – but possible cost issues

kt² may reach around 10%

• Replacing AlN by another material approach followed by Leti which is focusing on Lithium Niobate(LiNbO3 abbreviated as LNO) devices

kt² may reach 45% Leti’s thrust

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BAW resonators / filters with LNO


PZE RF d

evices

Targeted device performance• Tunability of center frequency and bandwidth

• Higher bandwidth

• Keeping high Q (>1000) to maintain low insertion loss and high rejection

Manufacturability• Oriented LNO films can’t be

sputtered layer transfer technology needed

• Possible use of Smart CutTM Processfor thin layers (< 1µm)Unique know-how at Leti on layer transfer

J.S. Moulet et al., “High piezoelectric properties in LiNbO3 transferred layer by the Smart CutTM technology for ultra wide band BAW filter applications”, IEEE IEDM 2008

Inspired from A. Reinhardt et al., «Acoustic filters based on thin single crystal LiNbO3 films: status and prospects», IEEE IUS 2014


MEMS microphones

PZE Senso

rs

• Tow trends in this market segment: More and more devices per smartphone and increasingly high SNR


Current MEMS microphones use capacitive detection

PZE Senso

rs

• The electrode is directly in the acoustic pathAcoustic resistance damping noise

• Holes size and density is key

• Small holes mean acoustic noise• Big holes mean less capacitance,

less gain and more electronic noise• Trade-off needed

• Only one way to solve this issue

• increasing holes density and diaphragm size

• To maintain compliance, the back volume must be increased too expensive, cumbersome

Back-plate electrode(with perforation holes)

Diaphragm

Microphone drawing: courtesy from InfineonBreakthrough needed


Towards high-SNR MEMS microphones

with piezoelectric or piezoresistive devices

PZE Senso

rs

Capacitive µphone with lateral electrodes

Capacitive µphone with electrodes in vacuum

No electrode in the acoustic path

Piezoresistive M&NEMS

microphone

• Very high sensitivity, relaxed ASIC

• But Flicker & Johnson noises

Piezoelectricmicrophone

Also developed by

• Low noise

• But low signal, hence sensitivity to parasitics

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CEA-Leti

The leading MEMS R&D lab working for industry

• 330 patents portfolio in the MEMS field

• 35 new patents/year

• More than 20 on-going industrial collaborations with major MEMS companies worldwide

• More than 20 industrial transfers

• 5 spin-offs / start-ups creationsIn sensors, actuators, energy micro-harvester and sensor packaging

• More than 30 years background in MEMS

• 200 people involved in MEMS (sensors, actuators, RF, packaging, process, characterization, IC design)

• 200 (and 300) mm in-house MEMS/NEMS technologies


current r&d challenges of the mobile mems market · | 4 •mostly based on si-based mems with...

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