mems accelerometers conquer high-end applications

MEMS accelerometers conquer high-end applications traditionally served by electrochemical devices

Philippe KrebsBusiness Development Manager, Colibrys (Switzerland) Ltd.

www.colibrys.com

Rosemont (IL), June 7, 2011Sensors Expo 20112

Smart Sensing SolutionsThe accelerometer market

After more than 20 years of existence, MEMS accelerometers are still progressing and market is growing!

Accelerometer in Automotive and Consumer market is tremendously growing– More than 22% growth for motion sensors in 2010– Motion sensors expected to surpass current leading MEMS products by 2014

MEMS accelerometers are more and more adopted by a wide variety of markets and applications

The evolution of the MEMS accelerometers performances opens new opportunities– Enabler of new applications (lower cost, lower power, smaller size…)– Replacement of traditional electromechanical solutions

High-end MEMS are getting ready to replace traditional electromechanical devices– MEMS to replace Vibrating quartz accelerometers, FBA or Geophones


Smart Sensing SolutionsMEMS Vs Electrochemical accelerometers types

Conventional coil based geophone

GS10031.7 x 35 mm124.7 grams

GS14 (Smallest)Ø 16.6 X 17.3 mm

19 grams

Q-Flex quartz

QA-2000Φ 25.5 x 24.6 mm

71 grams

High end MEMS

MS90108.9 x 8.9 mm x 3.2 mm

1,5 grams


Smart Sensing SolutionsHigh-end accelerometer market

Different categories of products are required for various markets and applications

Annual volume1 K 10 K 100 K 1 M 100 M

Low10 M

High

Perf

orm

ance

/ R

elia

bilit

y

High-end MEMS start to meet or even exceed performance and reliability requirementsHigh-end MEMS are enabler of new applications– Gun hard guided munitions (> 20’000g shocks)– High temperature and high reliability “Measurement While Drilling” (MWD up to 200°C)


Smart Sensing SolutionsHigh-end applications

Railway

Structure monitoring

Oil & Gaz - Drilling

Testing

Energy seismic imagingEarthquake monitoring

North findingPlatform stabilization

Guidance

Navigation

Aeronautics navigationAHRS

Tilt MEMS and open loop electronics

MEMS and close loop electronics

MEMS and close loop electronics


Smart Sensing SolutionsColibrys target high-end applications

Seismic

Inertial

Vibration

Tilt

Prod

ucts

Industrial EnergyMil / Aero

Markets

• Homeland security (13) • Geoseismic monitoring (8)• SHM (9) • Geotechnical (Mining) (10)

• Oil & gas exploration (6)• Structure monitoring (12)

• Drilling & survey (7)• High T MWD (1)

• Railway technology (3)• Testing (auto, aero) (15)• Process control (14)

• Platform stabilization (4)

• Navigation, guidance (5)• AHRS (2)• Flight recorder (11)• Gun hard guidance (7)


Smart Sensing SolutionsBenefits of MEMS technology

High end MEMS provide various benefits compared to electromechanical devices

Improvement of reliability– Through larger resistance to shocks and vibration

Improvement of some critical specifications– Shock survivability and post shock stability– Vibration Rectification Error– Temperature range– Noise level

Reduction of size and weight

Reduction of power consumption

Lower cost


Smart Sensing SolutionsLandscape of high-end accelerometer solutions

Bias StabilitySignal To Noise

1’000 ppm80 dB

100 ppm100 dB

10ppm120 dB

10

1’000

100

1ppm140 dB

10’000

Consumer / automotive grade MEMS

Electromechanical or vibrating quartz

Performance

Price [US $]

Hybrid MEMS close loopSF1500

Seismic imaging

New close loop MEMS

Hybrid MEMS open loop

RS9000

MS9000


Smart Sensing SolutionsEvolution of high-end MEMS accelerometers

Hybrid MEMS open loop products are bridging the gap and approaching electromechanical solutions– RS9000 is the latest evolution of open loop hybrid MEMS– Opportunity to provide lower cost solutions– Enabler for new applications

Hybrid MEMS close loop products will offer a new alternative and replace electromechanical devices– Some products already exist for seismic applications (Si-Flex products)– New sigma-delta servo will offer solutions to a wide range of applications– Real and qualified alternative enabling new applications

Two main axis for the evolution of Colibrys products


Smart Sensing SolutionsWhat is the adequate MEMS technology?

Bulk micromachining combined with hybrid assembly offer the best opportunity for high-end performances!

Manufacturing

Capacitor

Mass

Gap control

Sensor design

- Larger in size- Only one axis- Hybrid assembly- Longer etching timedue to mass thickness (>350µm).

- More expensive and larger but better performances (no compromises)

- Smaller in size- Up to three axispossible with one single die

- Monolithic- MEMS above IC- Rapid etching due to small thickness of the mass (thickness ~5 to 10µm).

- Lower manufacturing cost

- 2 x 15 to 50pF- Much larger capacitances: required for

low noise and high stability

- 2 x 2 to 5pF- Larger noise and lower stability

- 5 to 15 milligrams- Much lower Brownian noise and better stability due to larger mass

- 0.03 to 0.3 milligrams-Larger noise and lower stability

- Thick proof mass- Gap control by oxide growth (precision 1.5%) -Gap of ~2µm ±300Å

- Thin proof mass- Gap control by photolithography and DRIE etching (precision 17%)

- Gap of ~4 to 6µm ±10’000Å

- Out of plan displacement

- In plandisplacement

Bulk micro-machiningSurface micro-machining


Smart Sensing SolutionsOut of plane MEMS Silicon sensor

Design featuresOut of plane mass movementLarge mass– 5 to 15 mgLarge capacitive signal – 15 to 50 pF/µmStoppers to limit mass movementNew design for immunity against assembly stressSqueeze film damping control

Basic sensor technologyBulk silicon micromachining chip– Wet and DRIE etching

Assembly of 3 wafers:– High temp. Fusion Bonding (SFB)– Sealing at low and controlled

pressure Full functional test at wafer level, including capacitive response

Silicon die packaged in ceramics housing


Smart Sensing SolutionsKey performances of MEMS Silicon sensor

Low Brownian noise of the sensor– Inertial design: 0.5 µg/√Hz– Seismic design: 20 ng/√Hz

Shock resistant– >25’000g on real products– Up to 40’000g demonstrated by centrifuge

Stress reduction through die attach process– shift of proof mass after one year lifing* process < 0.03 nm

(* lifing including ageing, temperature storage, temperature cycles and shocks)

Control of the damping– damped to Q > 120

Small size

This new MEMS element is capable to meet high end requirements


Smart Sensing Solutions

High performance open-loop sensors(RS9000)


Smart Sensing SolutionsOpen loop architecture

Multichip module– MEMS, ASIC and auxiliary electronic

Principle– Acceleration deflects proof mass– Proof mass deflection is a capacitive

measurement

Capacitor bridge– Linear and ratiometric output

MassSpring


Smart Sensing SolutionsStandard vs. improved open-loop performance

Comparison of Colibrys open-loop capabilities (valid for a 10g product)– MS9010– RS9010



Sigma-delta closed loop sensors


Smart Sensing SolutionsClose-loop sensor - Systems architecture

Capacitive bulk micromachined MEMS sensor

Analog low noise amplifier with ADC

Digital loop filter

Electrostatic force feed-back– pulses of constant amplitude and duration applied to either side of the proof mass

MEMS FPGA

ADC

DAC (1 bit)

Digital Filter Decimation

Analog Front -end ASIC

Servo loop electronic

Mass

TOP

CTR

BOT


Smart Sensing SolutionsOpen-loop / Close-loop performance overview

Further improvement are expected from the close loop electronic

Comparison of Colibrys open-loop capabilities vs close loop– RS9010– Colibrys close-loop


Smart Sensing SolutionsNoise modeling and measurement 10 g FS

Modeling: – Matlab model – Sensor and electronics– All known noise sources

Measurement– 1 g position– Low noise lab

Good agreement between modeling and measurement

Typical sigma delta noise shaping


Smart Sensing SolutionsExpected performance for low noise applications

Modeling of 1.8 g sensor– MEMS seismic design with low

Brownian noise: 20ng/√Hz and high gain (large capacitors)

– Optimized system loop

Modeling results– Noise floor: 30 ng/√Hz– Dynamic range: 155dB 1 Hz BW

Reference: Class A acc.– Noise: 100 ng/√Hz– 130 dB 50 Hz BW

– Opportunity to replace FBA acc.Model: Seismic ± 1.8 g sensor

0.8 g vibration @100 Hz + 1 g static

The same technology can fulfill low noise seismic requirements


Smart Sensing SolutionsMEMS Close-loop vs Electromechanical

Comparison of MEMS close-loop with electromechanical device– Colibrys close-loop– QA2000-30 / 60g


Smart Sensing SolutionsSummary table

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Examples of high-end applications


Smart Sensing SolutionsColibrys accelerometer for seismic imaging applications

Land and Oceanic oil & gas seismic exploration

Displacement of 1D analog geophones by 3D digital MEMS geo-sensors

Benefits:– Increased predictability– Depth of discovery (5’000m)– More accuracy

Conventional coil-based geophones

VectorSeis® multi-component digital sensor


Smart Sensing SolutionsColibrys accelerometer for mining applications

Seismic exploration by reflection seismology

– Mineral exploration– Mine planning and engineering– Detect gas and water pockets– Detect special geological fractures– Mining Safety

Benefits:– Highly sensitive detection of low

frequency signals produced from human-induced movements (e.g. explosions, construction, movements)


Smart Sensing SolutionsColibrys accelerometer for building & SHM applications

Structural monitoring of :– Buildings– Bridges– Towers– Tunnels– Dams– Pipeline

Benefits:– To monitor the state-of-health of a structure

over time to study effects ageing or deterioration due to overstraining, earthquake movement

Oil or gas reservoir

Amplified signal from floor to roof


Smart Sensing SolutionsColibrys accelerometer for directional drilling applications

Measurement while drilling (MWD)

Benefits:– Measure on line and guide the drilling head to

the targeted location.

Function of accelerometer:– Inclination provided by accelerometer and

Azimuth by a magnetometer.– Need rugged, high precision and high

temperature sensors (harsh environment). Directional drilling

Oil or gas reservoir


Smart Sensing SolutionsColibrys accelerometer for train applications

Magnetic levitation control system for Maglev System Transrapid

Function of accelerometer:– Measure distance between the rails and the

electromagnets about 10mm !

Custom product: MS8020TBD qualified– 128 sensors per section (2 up to 10 sections)

± 20g, 1.6 kHz @±20%

Shangai city – International airport (40 km)

Several projects on going in China, US, Brazil, UK

Transrapid: Flying on the ground (430 km/h)

Vehicle guides by an electronic gap control system

10 mm

10 mm



High-speed train tilt control system

Benefits:– Improve the running speed on curved tracks

20-30% (shortening the travel time)– Enhance the ride comfort

Function of accelerometer in tilting mechanism:– Measure lateral acceleration at bogie level in a

curve and then compensate for lateral movement by applying a tilting force. Tilting train



High-speed train vibration monitoring system for early fault detection and prevention:– Bogie instability– Derailment detection– Rail track conditions– Wheel flat and shape

Benefits:– Increased safety and reliability– Reduced maintenance cost– Root cause analysis– Improved maintenance planning capabilities

Function of acc:– Measure vertical and/or lateral vibration

High tech bogies incorporating Colibrys MEMS accelerometers


Smart Sensing SolutionsColibrys accelerometer for AHRS applications

Attitude Heading and Reference System (AHRS) are 3-axis sensors that provide: – Heading, – Attitude, – Yaw information for aircraft or a subject moving

in free space (land, see and wafter)

Benefits– Cheaper system (5k – 100k USD)– Smaller system– Superior reliability and accuracy

Function of accelerometer in an AHRS:– Determine initial attitude of AHRS reference

(leveling) – Provide attitude corrections during the flight by

correcting the gyro drift in tilt (pitch, roll) – AHRS accelerometers require an overall error

not exceeding 2 mg AHRS

Acc Gyro

MagnetometersGPS


Smart Sensing SolutionsConclusion

High stability MEMS dies, combined with improved open-loop electronics or sigma delta servo system demonstrate very high performance– Bias stability– Noise – Linearity / vibration rectification

The same technology is well adapted for wide range of applications:– Inertial: Navigation, AHRS, Platform stabilization, Down-borehole drilling– Seismic: Seismic imaging, Earthquake monitoring, Structural Health Monitoring

MEMS offers similar performances compared to well established electromechanical accelerometers with some advantages such as:– Lower cost, smaller size, low power consumption, higher robustness and improved

reliabilityMEMS accelerometers are on their way to become the leading technology

for high-end inertial, seismic, vibration or tilt applications,

replacing various classical technologies such as Electromechanical, FBA or geophones!



Thank you for your attention

Visit us at booth 403

mems accelerometers conquer high-end applications

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