Overview
Micro-electro-mechanicalsystem(MicroElectro-MechanicalSystem,MEMS),referredtoasmicro-machine,isbasedonmicro-electronicsAnewtechnologybasedontechnologyandmicromachiningtechnology.Asearlyasthe1960s,withtheemergenceanddevelopmentofmicroelectronicstechnology,somecreativescientistsbegantoexploretheuseofsiliconmicromachiningmethodstomakesensors,actuatorsandcontrollers,andimaginedintegratingtheminatinygeometricspace.Inordertoformahighlyautomated,intelligent,mass-produced,low-costmicroelectronicmechanicalsystem.Butatthisstage,thereisnomatureprocessingtechnologyformakingmicromechanicalstructuresanddevices.Micromachineryisjustaconceptordesignidea.Inthe1980s,large-scaleintegratedcircuittechnologyhadmatured.PeopleusedICtechnologytosuccessfullyfabricatemicro-mechanicalpressuresensorsandaseriesofmicro-mechanicalcomponentssuchasmicrohinges,microconnectingrods,andmicrogears.Micromechanicsisanemergingfrontierdisciplinethatemergedinthelate1980s.
Developmentsituation
Semiconductorsensor-photoresistorappearedasearlyas1941,butitwasnotdevelopeduntiltheappearanceofintegratedcircuitsinthe1970s.Theinventionoftransistorsandintegratedcircuitspromotedthecombinationofelectroniccircuitsandstructuralsensorsontheonehand,andontheotherhandenabledpeopletousesolid-statephysicalpropertiestomakesensors,whichledtotheemergenceofphysicalpropertiessensors,ofwhichsemiconductorsensorsarethemostimportantone..Becausesemiconductormaterials(especiallysilicon)aresensitivetovarioussignalssuchasforce,heat,andmagnetism,andcanuseadvancedprocesstechnologytodevelopintegratedcircuits,semiconductorsensorshaveverticalsensitivity,photosensitive,magnetic,gas,andionsensitivity.Varioustypesofproductssuchasbiosensitivity.Sinceplanartechnologycanbeused,semiconductorsensorsalsohavethepotentialforminiaturization.Throughcontinuousefforts,peoplehavedevelopedavarietyofmicro-sensors,someofwhichhaveintegratedsimplesignalprocessingcircuits,whichalsolaidthefoundationfortheemergenceofmicro-machining(MicroMachining)technology.Withthecontinuousexpansionofthecontentandlevelofmicro-machiningtechnology,micro-machiningtechnologyhasbecomethekeytechnologyofforce-sensitivesensorsandhasexpandedthescopeofapplication.
Therapiddevelopmentofmicro-machiningtechnologyhasledtothebirthofmicro-actuators.Peoplehaverealizedinpracticethatsiliconmaterialsnotonlyhaveexcellentelectricalandopticalproperties.Theemergenceofmicro-machiningtechnologyhasmadeitpossibletomakesiliconmicro-mechanicalparts.Intheearly1980s,somevisionaryscientistsproposedtheconceptofmicromechanicalactuators.In1987,FanLongshengoftheUniversityofCaliforniaatBerkeleyandothersusedsurfacemicromachiningtomakepolysilicongears,whichcausedashockintheinternationalacademiccommunity.Subsequently,themicro-machinedmulti-channelabsolutepressuresensorforautomobileswasputintomassproduction,whichindicatedthatMEMStechnologyhasemergedasanimportantinterdisciplinarysubject.
In1988,theUniversityofCaliforniaatBerkeleyfirstsuccessfullydevelopeda60umelectrostaticmicromotorusingICtechnology.Thisachievementcausedasensationintheworld,anditmarkedthatmicromechanicaltechnologyhasdevelopedintoanindependentemergingdiscipline.Man’sabilitytounderstandandtransformthemicrocosmhasalsoenteredanewstage.Asthehigh-techandpotentiallyhugehigh-techindustryofthe21stcentury,micro-machineryhasattractedtheattentionofallcountriesintheworld.NumerousuniversitiesandscientificresearchesathomeandabroadAndtheindustrysectorisconductingextensiveandin-depthresearch.Micro-machinesarenottraditionalmachinesthataresimplyminiaturizedinscale.Whenthefeaturesizereachesthemicronlevel,themechanicalsystemcharacteristicsofmicro-machines,thephysicalpropertiesofmaterialsandtheirresponsetoenvironmentalchangesareverydifferentfromtraditionalmachines.Usuallyreferstoamicro-electromechanicalsystemthatintegratesmicro-mechanisms,micro-drives,micro-energysources,micro-sensors,controlcircuits,andsignalprocessingdevicesthatcanbeproducedinbatches.Therefore,itisfarbeyondtheconceptandscopeoftraditionalmachinery.Micromechanicsistheanalysisanddesignofmicromachinesbasedonthestudyofmicroscalemechanicalpropertiesandmechanicalpropertiesofmicrocomponents,andthedevelopmentofmechanicaldeviceswithstructures,materials,functionsandprinciplesdifferentfromtraditionalmachines.
SinceSchockley,Bardeen,andBrattaininventedthetransistorin1947,microelectronicstechnologyhasdevelopedbyleapsandbounds.In1953,CharlesS.Smithstudiedthepiezoresistiveeffectofsemiconductors.KuliteCompanyintroducedisotropicandanisotropiccorrosiontechnologiesin1970and1976,respectively.NationalSemiconductorintroducedmass-producedpressuresensorstothemarketin1974.In1982,theterm"micromachine"cameintobeing.Atthistime,bulksiliconmicromachiningtechnologyhasbecomeaneffectivemeansofmakingmicromechanicaldevices.In1985,thesacrificiallayertechnologywasintroducedintomicro-machining,andtheconceptof"surface"micro-machiningwasborn.In1987,U.C.Berkeleyusedmicro-machiningtechnologytoproducetheworld'sfirstmicro-electrostaticmotor,whichopenedanewpageinthedevelopmentofmicro-machines.During1987-1988,aseriesofacademicconferencesonmicromechanicsandmicrodynamicswereheld.ThetermMEMSwaswidelyadoptedintheseconferencesandgraduallybecameaworldwideacademicterm.In1993,ADIsuccessfullycommercializedminiatureaccelerometersandappliedthemtoautomotiveanti-collisionairbagsinlargequantities,markingthebeginningofcommercializationofMEMStechnology.
Becauseoftheepoch-makingsignificanceofMEMS,countriesallovertheworldarepayinggreatattentiontoitsdevelopmentandhavegivenstrongsupportinbothhumanandmaterialresources.Accordingtostatisticsfromrelevantagencies,thecountriesandregionswiththemostactiveMEMSR&DactivitiesaretheUnitedStates,Germany,Japan,Scandinavia,France,China,SouthKorea,theUnitedKingdom,Sweden,andTaiwan.
StructureandSignificance
Micro-machineryhasbroadapplicationprospects,anditsappearancewillundoubtedlyhaveaprofoundimpactonthefuturedevelopmentofvarioussectorsofthenationaleconomyanddefenseindustry.Micromotorisanindependentmicrominiaturizedelectromechanicalsystem,whichismainlycomposedofseveralelementssuchasmicrodrive,microsensor,microactuator,microcontroller,andenergy.Micro-drivesrepresentedbymicro-motorshavealwaysbeenoneofthekeytechnologiesandresearchhotspotsofmicro-mechanicalsystems.Thetechnicallevelofmicro-motorsreflectstoacertainextenttheaspectsofmicro-mechanicaldevelopmentinacountry.Electromagneticmicro-motorshavesomeadvantagesthatothertypesofmotorscan’tmatch,andtheyareoneofthemostpromisingmicro-drives.Formorethantenyears,peoplehavedesignedandmanufacturedelectromagneticmicromotorsofvariousformsandstructures,butthedesigntheoryandexperimentalresearchofelectromagneticmicromotorsarestillinthestageofexplorationandperfection,andthereisnounifiedstandardforthestructureandsizeofmicromachines.Accordingtoacustomaryclassification,thosewithastructuresizeof1mmto10mmarecalledMinimechanism;thosewithastructuresizeof1micronto1mmarecalledSubmicromechanisms,whicharecollectivelyreferredtoas"micromechanics."0.1nanometersto0.1micrometersarecallednanomachines.
Thewaveofcommercializationtriggeredbymicro-machines
ThefirstwaveofcommercializationofMEMSbeganinthelate1970sandearly1980s,whenlarge-scaleetchedsiliconwaferstructuresandback-etchedfilmswereused.Sheetmakingpressuresensor.Becausethethinsilicondiaphragmisdeformedunderpressure,itwillaffectthewiringofthevaristoronitssurface.Thischangecanconvertthepressureintoanelectricalsignal.Latercircuitsincludedcapacitivesensingmovingmassaccelerometers,usedtotriggercarairbagsandpositioninggyroscopes.
Thesecondroundofcommercializationappearedinthe1990s,mainlyaroundtheriseofPCandinformationtechnology.TIhasintroducedaprojectorbasedonanelectrostaticallydrivenobliquemicromirrorarray,butthermalinkjetprintheadsarestillpopular.
Thethirdroundofcommercializationcanbesaidtohaveoccurredattheturnofthecentury.Micro-opticaldeviceshavebecomeasupplementtoopticalfibercommunicationthroughall-opticalswitchesandrelateddevices.Althoughthemarketissluggish,micro-opticaldeviceswillbeastronggrowthareaforMEMSinthelongrun.
OtherapplicationsthataredrivingthefourthroundofcommercializationincludesomeRFpassivecomponents,audio,biologicalandneuronprobesmadeonsiliconchips,andthedevelopmentofso-called"labonachip"biochemicaldrugsStaticandmobilecomponentsofthesystemandmicro-drugdeliverysystem.PartoftherecentincreaseinattentiontoMEMScomesfromsurfacemicromachiningtechnology,whichdissolvesthesacrificiallayer(thematerialthatseparatesotherlayerswhenthestructureismade)inthelaststeptogenerateasuspendedthinmobileresonantstructure.
Futuredevelopmenttrends
(1)Diversifiedresearchdirections.Judgingfromthepapersofpreviouslarge-scaleMEMSinternationalconferences,theresearchonMEMStechnologyhasbecomeincreasinglydiversified.ThefieldsofMEMStechnologymainlyincludeinertialdevices(suchasaccelerometersandgyroscopes),atomicforcemicroscopes,datastorage,three-dimensionalmicrostructureproduction,microvalves,pumpsandmicronozzles,flowdevices,microopticaldevices,variousactuators,microPerformancesimulationofelectromechanicaldevices,variousmanufacturingprocesses,packagingandbonding,medicaldevices,experimentalcharacterizationdevices,pressuresensors,microphones,andacousticdevices,etc.Thecontentinvolvesvariousapplicationfieldssuchasmilitaryandcivilianuse.
(2)Diversifiedprocessingtechnology.Theprocessingtechnologybeingusedandstudiedincludestraditionalbulksiliconprocessingtechnology,surfacesacrificiallayertechnology,siliconmeltingtechnology,deepgrooveetchingandbondingcombinedprocessingtechnology,SCREAMtechnology,LIGAprocessingtechnology,thickglueandelectroplatingcombinationThemetalsacrificiallayerprocess,MAMOSprocess,bulksiliconprocessandsurfacesacrificiallayerprocessarecombined,andthespecificprocessingmethodsaremorediverse.
(3)Systemmonolithicintegration.Theoutputsignal(currentorvoltage)ofthegeneralsensorisveryweak.Ifitisconnectedtoanexternalcircuit,theinfluenceofparasiticcapacitance,resistance,etc.willcompletelycoveruptheusefulsignal.Therefore,itisimpossibletoobtainthequalitybyusingthesensitiveelementtoconnecttotheprocessingcircuit.Forverytallsensors,onlybyintegratingthetwoononechipcantheyhavethebestperformance.
(4)UnifiedconsiderationofMEMSdevicechipmanufacturingandpackaging.ThemaindifferencebetweenMEMSdevicesandintegratedcircuitchipsis:MEMSdevicechipsgenerallyhavemovingparts,whicharerelativelyfragileandarenotconducivetotransportationbeforepackaging.Therefore,MEMSdevicechipmanufacturingandpackagingshouldbeconsideredinaunifiedmanner.PackagingtechnologyisanimportantresearchfieldofMEMS.AlmosteveryMEMSinternationalconferencehasspecialdiscussionsonpackagingtechnology.
(5)Commoncommerciallow-performanceMEMSdevicescoexistwithhigh-performancespecial-purpose(suchasaviation,aerospace,military)MEMSdevices.Forexample,accelerometers,therearealargenumberofaccelerometerswithhigheconomicvaluethatonlyrequireanaccuracyof0.5gormoreandcanbewidelyusedinautomobileairbags,andtherearealsoaccelerometersthatrequireanaccuracyof10-8gandcanbeusedinaerospaceandotherhighAccelerometersinthefieldoftechnology.Forthegyro,therearealsosomecaseswheretheaccuracyisrequiredtobe0.1°/hour,andsomeonlyrequire10000°/hour.