Presentation on theme: "MEMS Applications in Seismology"— Presentation transcript:
1 MEMS Applications in Seismology Nov 11, 2009Seismic Instrumentation Technology SymposiumB. John MerchantTechnical StaffSandia National LaboratoriesSandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
2 Outline Overview of MEMS Technology MEMS Accelerometers Seismic RequirementsCommercial AvailabilityNoise & Detection TheoryCurrent R & D EffortsOutlook
3 What are MEMS?Micro-Electro-Mechanical Systems (MEMS) Features range from 1 to 100 microns. Similar fabrication techniques as Integrated Circuits (IC). However, MEMS fabrication is a trickier process due to the incorporation of mechanical features Distinguished from traditional mechanical systems more by their materials and methods of fabrication than by feature size.Courtesy of Sandia National Laboratories, SUMMiTTM Technologies,
4 What are MEMS? Materials Fabrication Applications Silicon Polymers Single-crystal silicon makes a nearly perfect spring with very stable material properties.PolymersMetalsgold, nickel, chromium, titanium, tungsten, platinum, silver.DepositionElectroplatingEvaporationSputteringLithographyPhoto, Electronic, Ion, X-rayEtchingWet Etching: Bathed in a chemical solventDry Etching: Vapor/PlasmaAutomotive air bagsInkjet printersDLP projectorsConsumer Electronics (Cell phone, Game Controllers, etc)Sensors (pressure, motion, RF, magnetic, etc)
5 Microfabrication Technologies Three Dominant MEMSMicrofabrication TechnologiesStructures formed by wet and/or dry etching of silicon substrateBulk MicromachiningSurface MicromachiningStructures formed by deposition and etching of sacrificial and structural thin filmsLIGAWet Etch PatternsDry Etch PatternsSiliconSubstrateGrooveNozzlep++ (B)MembraneChannelsHolesSilicon SubstratePoly SiMetal MoldStructures formed by mold fabrication, followed by injection moldingCourtesy of SNL MEMS Technology short course
6 Increasing Commercialization MEMS History1989 – Lateral Comb drive at Sandia National Laboratories197019751980198519901995200020052009Decreasing CostsIncreasing Commercialization1970’s - IBM develops a micro-machined pressure sensor used in blood pressure cuffs1986 – LIGA process for X-ray lithography enable more refined structures1991 – Analog Devices develops the first commercial MEMS accelerometer for air bag deployment (ADXL50)DecreasingCostsIncreasing Commercialization1994 – Deep Reactive-Ion Etching (DRIE) process developed by Bosch.HP develops inkjet cartridges using micro-machined nozzles1988 – first rotary electro-static drive motors developed at UC Berkley1993 – Texas Instruments begins selling DLP Projectors with Digital Mirrors.
7 MEMS Commercial Applications Ink Jet CartridgeHewlett PackardDigital Mirror DeviceTexas InstrumentsAccelerometerAnalog DevicesMicromirror switchLucent TechnologiesThese are examples of MEMS Technologies which have transformed their market. Every new automobile will have multiple accelerometer, pressure sensors, etc. which can be manufactured cheaply in high volume by MEMS.Pressure SensorBosch MEMSCourtesy of SNL MEMS Technology short course
8 MEMS Accelerometer History 2002 – Applied MEMS (now Colibrys) releases low-noise Si-Flex Accelerometer:+/- 3 g Peak300 ng/√Hz Noise19911993199519971999200120032005200720091991 – Air Bag Sensor Analog Devices (ADXL50)+/- 50 g Peak6.6 mg/√Hz Noise2006 – Nintendo Wii Controller (Analog Devices ADXL330).+/- 3 g Peak350 ug/√Hz NoiseImprovements in performance2004 – Colibrys VectorSeis Digital 3 Channel Accelerometer2 – 1000 Hz+/ g Peak~50 ng/√Hz Noise2005 – Sercel 428XL-DSU32 – 800 Hz+/- 0.5 g Peak~40 ng/√Hz Noise
9 What makes a MEMS Seismometer A MEMS Accelerometer with:Low noise floor (ng’s/√Hz)~1 g upper rangeHigh sensitivityModeled as a spring-mass systemProof mass measured in milli-gramsBandwidth below the springs resonant mode (noise and response flat to acceleration)
10 Seismology Requirements Noise floor(relative to the LNM)Peak acceleration(Strong vs weak motion)SensitivityLinear dynamic rangeBandwidth(short-period, long-period, broadband)HighNoiseModelLowNoiseModelCurrent Best MEMSSP Target RegionGS13KS54000Requirements are ultimately application dependent
11 Strong Motion Requirements Many of the strong motion requirements may be met by today’s MEMS Acclerometers:Noise< 1 ug/√HzBandwidth> 1-2 HzPeak Acceleration1-2 g’sDynamic Range~100 dB
12 Weak Motion Requirements Weak motion requirements are more demanding:Noise< 1 ng/√HzBandwidthSP: 0.1 Hz to 10’s HzLP: < 0.01 Hz to 1’s HzBB: 0.01 Hz to 10’s HzPeak Acceleration< 0.25 gDynamic Range>120 dBThere are no MEMS accelerometers available today that meet the weak motion requirements.
13 Commercially Availability There are many manufacturer’s of MEMS Accelerometers. Most are targeted towards consumer, automotive, and industrial applications. Only a few approach the noise levels necessary for strong-motion seismic applicationsManufacturersAnalog DevicesBosch-Sensortec*Colibrys*EndevcoFreescale*GeoSIG*KinemetricsKionixMEMSIC*PCB*ReftekSilicon DesignsSTMicroelectronicsSummit Instruments*Sercel*Wilcoxon*Noise Floor < 1 ug/√Hz
14 Capacitive Force Feedback ColibrysFormerly Applied MEMS, I/O.Oil & Gas ExplorationProduces VectorSeis which is sold through ION (www.iongeo.com)ManufacturerColibrysModelSF 1500SF 2005SF3000Digital-3*TechnologyCapacitiveCapacitive Force FeedbackOutputAnalogDigitalFormatChipModuleAxis13Power100 mW140 mW200 mW780 mWAcceleration Range+/- 3 g+/- 4 g+/- 0.2 gFrequency Response0 – 1500 Hz0 – 1000 Hz0 – HzSensitivity1.2 V/g500 mV/g58 ng/bitSelf Noise300 – 500 ng/√Hz800 ng/√Hzng/√Hz100 ng/√HzWeightNot SpecifiedSize24.4 x 24.4 x 16.6 mm24.4 x 24.4 x 15 mm80 x 80 x 57 mm40 x 40 x 127 mmShock Range1500 g1000 gTemperature-40 to 125 ◦C-40 to 85 ◦C*discontinued
15 39 ng/√Hz @ 2 Hz 11 ng/√Hz @ 10 Hz 4 ng/√Hz @ 100 Hz Endevco, PCB, WilcoxonManufacturerEndevcoModelModel 86Model 87TechnologyPiezoelectricOutputAnalogFormatModuleAxis1Power200 mWAcceleration Range+/- 0.5 gFrequency Response0.003 – 200 Hz0.05 – 380 HzSensitivity10 V/gSelf Noise39 2 Hz Hz Hz90 2 Hz HzHzWeight771 grams170 gramsSize62 x 62 x 53 mm29.8 x 29.8 x 56.4 mmShock Range250 g400 gTemperature-10 to 100 ◦C-20 to 100 ◦CNot strictly MEMS, but they are small and relatively low-noise.All three companies make fairly similar Piezoelectric accelerometersIndustrial and Structural applications
16 Kinemetrics Strong motion, seismic measurement ManufacturerKinemetricsModelEpiSensor ES-TEpiSensor ES-U2TechnologyCapacitive MEMSOutputAnalogFormatModuleAxis31Power144 mW100 mWAcceleration Range+/ gFrequency Response0 – 200 HzSensitivity10 V/gSelf Noise60 ng/√HzWeightNot Specified350 gramsSize133 x 133 x 62 mm55 x 65 x 97mmShock RangeTemperature-20 to 70 ◦CStrong motion, seismic measurementForce Balance AccelerometerAvailable in single and three axis configurations
17 ReftekStrong motion measurement for seismic, structural, industrial monitoringAvailable in single, three axis, and borehole configurationsManufacturerReftekModel131A*TechnologyCapacitive MEMSOutputAnalogFormatModuleAxis3Power600 mWAcceleration Range+/- 3.5 gFrequency Response0 – 400 HzSensitivity2 V/gSelf Noise200 ng/√HzWeight1000 gramsSize104 x 101 x 101 mmShock Tolerance500 gTemperature-20 to 60 ◦C* uses Colibrys Accelerometers
18 Sercel Used in tomography studies for Oil & Gas Exploration ManufacturerSercelModelDSU3-428TechnologyCapacitive MEMSOutputDigitalFormatModuleAxis3Power265 mWAcceleration Range+/- 0.5 gFrequency Response0 – 800 HzSensitivityNot SpecifiedSelf Noise40 ng/√HzWeight430 gramsSize159.2 x 70 x 194 mmShock RangeTemperature-40 to 70 ◦CUsed in tomography studies for Oil & Gas ExplorationSold as complete turn-key systems and not available for individual sales
19 MEMS accelerometers Advantages Disadvantages Small Can be low power, for less sensitive sensors.High frequency bandwidth (~ 1 kHz)DisadvantagesActive device, requires powerPoor noise and response at low frequencies (< 1 Hz), largely due to small mass, 1/f noise, or feedback control corner.Noise floor flat to acceleration, exacerbates noise issues at low frequency (< 1 Hz)
20 Thermo-mechanical noise for a cantilevered spring Theoretical NoiseThermo-mechanical noise for a cantilevered springTwo main sources of noise:Thermo-mechanicalBrownian motionSpring imperfectionsElectronicElectronicsDetection of mass positionNoise characteristics unique to detection techniquean = 2.3 x 10^-9 m / s2 / √Hz= 0.2 ng / √HzBoltzman’s Constant kB=1.38x10-23 J/KTemperature T = 300 KResonant Frequency wo= rad/s (50Hz)Quality Factor Q = 1000Proof Mass m = 1 gram (10-3 kg)Traditional SeismometerMEMS AccelerometerLarge mass (100’s of grams)Small mass (milligrams)Thermo-mechanical noise is smallThermo-mechanical noise dominatesElectronic noise dominatesSame electronic noise issue as traditional
21 Detection of mass position Variety of ways to determine mass-positionPiezoelectric / PiezoresistiveCapacitiveInductiveMagneticFluidicOptical (diffraction, fabry-perot, michelson)
22 Capacitive DetectionThe most common method of mass position detection for current MEMS accelerometers is capacitive. Capacitance is a weak sensing mechanism and force (for feedback contrl) which necessitates small masses (milligrams) and small distances (microns). Feedback control employed for quietest solutions. Differential sampling for noise cancelation.Colibrys bulk-micromachined proof mass sandwiched between differential capacitive platesSilicon Designs capacitive plate with a pedestal and torsion bar.
23 R&D ChallengesLarge proof mass and weak springs required. This makes for a delicate instrument.Capacitance less useful as a detection and feedback mechanism for larger masses.Feedback control required to achieve desired dynamic range and sensitivity.R&D requires access to expensive MEMS fabrication facility1/f electronic noise could limit low-frequency
24 DOE Funded R&D Projects Several posters on displayAdditional details and proceedings available atCharacteristics:Significantly larger proof mass (0.25 – 2 grams)Non-capacitive mass position sensing (inductive, optical, fluidic)Feedback control
25 DOE Funded R&D Projects Kinemetrics / Imperial CollegeInductive coil with force feedbackProof mass of gramsHz bandwidth, resonant mode at 11.5 HzDemonstrated noise performance of 2-3 ng/√Hz over 0.04 – 0.1 Hz, higher noise at frequencies > 0.1 HzSymphony AcousticsFabry-Perot optical cavityProof mass of 1 gramHz bandwidthDemonstrated noise performance of 10 ng/√HzTheoretical noise performance of 0.5 ng/√Hz
26 DOE Funded R&D Projects Photo DiodesReflective SurfaceFolded SpringsSandia National LaboratoriesLarge proof mass (1 gram, tungsten)Meso-scale proof mass with MEMS diffraction grating and springs.Optical diffraction gratingTheoretical thermo-mechanicalnoise 0.2 ng/√Hz over 0.1 to 40 HzOptical GratingProof Mass FrameProof MassFixed FrameSilicon AudioLarge proof mass (2 gram)Meso-scale construction with MEMS diffraction gratingOptical diffraction grating0.1 to 100 Hz target bandwidthTheoretical thermo-mechanical noise 0.5 ng/√Hz over 1 to 100 Hz
27 DOE Funded R&D Projects PMD Scientific, Inc.Electrochemical fluid passing through a membraneTheoretical noise 0.5 ng/√Hz over 0.02 to 16 HzMichigan Aerospace Corp.Whispering Gallery SeismometerOptical coupling between a strained dielectric microsphere and an optical fiberTheoretical noise of 10 ng/√Hz
28 5 year outlookOver the next 5 years, there is a strong potential for at least one of the DOE R&D MEMS Seismometer projects to reach the point of commercialization.This would mean a MEMS Accelerometer with:a noise floor under the < LNM (~ 0.4 ng/√Hz)Bandwidth between 0.1 and 100 Hz,> 120 dB of dynamic rangesmall ( < 1 inch^3).Low power (10’s mW)
29 Enabling Applications Flexible R&D deploymentsWhy simply connect a miniaturized transducer onto a traditional seismic system?Will require highly integrated packages:DigitizerMicrocontrollerGPSFlash storageCommunicationsBatteryPower SourceAntennaBattery BackupRadio / EthernetorientationStorageWaveformsParametersDetection templatesCompassMicroprocessorData RetrievalAlgorithmsCommunicationsGPSlocation, timewaveformtime series3-axisAccelerometer
30 10 year outlookMEMS Accelerometers have only been commercially available for ~18 years.Where were things 10 years ago?Further expansion into long period (~ 0.01 Hz)Small, highly integrated seismic systems