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
Rosemont (IL), June 7, 2011Sensors Expo 20113
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
Rosemont (IL), June 7, 2011Sensors Expo 20114
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)
Rosemont (IL), June 7, 2011Sensors Expo 20115
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
Rosemont (IL), June 7, 2011Sensors Expo 20116
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)
Rosemont (IL), June 7, 2011Sensors Expo 20117
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
Rosemont (IL), June 7, 2011Sensors Expo 20118
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
Rosemont (IL), June 7, 2011Sensors Expo 20119
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
Rosemont (IL), June 7, 2011Sensors Expo 201110
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
Rosemont (IL), June 7, 2011Sensors Expo 201111
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
Rosemont (IL), June 7, 2011Sensors Expo 201112
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
Rosemont (IL), June 7, 2011Sensors Expo 201113
Smart Sensing Solutions
High performance open-loop sensors(RS9000)
Rosemont (IL), June 7, 2011Sensors Expo 201114
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
Rosemont (IL), June 7, 2011Sensors Expo 201115
Smart Sensing SolutionsStandard vs. improved open-loop performance
Comparison of Colibrys open-loop capabilities (valid for a 10g product)– MS9010– RS9010
Rosemont (IL), June 7, 2011Sensors Expo 201116
Smart Sensing Solutions
Sigma-delta closed loop sensors
Rosemont (IL), June 7, 2011Sensors Expo 201117
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
Rosemont (IL), June 7, 2011Sensors Expo 201118
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
Rosemont (IL), June 7, 2011Sensors Expo 201119
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
Rosemont (IL), June 7, 2011Sensors Expo 201120
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
Rosemont (IL), June 7, 2011Sensors Expo 201121
Smart Sensing SolutionsMEMS Close-loop vs Electromechanical
Comparison of MEMS close-loop with electromechanical device– Colibrys close-loop– QA2000-30 / 60g
Rosemont (IL), June 7, 2011Sensors Expo 201123
Smart Sensing Solutions
Examples of high-end applications
Rosemont (IL), June 7, 2011Sensors Expo 201124
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
Rosemont (IL), June 7, 2011Sensors Expo 201125
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)
Rosemont (IL), June 7, 2011Sensors Expo 201126
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
Rosemont (IL), June 7, 2011Sensors Expo 201127
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
Rosemont (IL), June 7, 2011Sensors Expo 201128
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
Rosemont (IL), June 7, 2011Sensors Expo 201129
Smart Sensing SolutionsColibrys accelerometer for train applications
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
Rosemont (IL), June 7, 2011Sensors Expo 201130
Smart Sensing SolutionsColibrys accelerometer for train applications
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
Rosemont (IL), June 7, 2011Sensors Expo 201131
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
Rosemont (IL), June 7, 2011Sensors Expo 201132
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!