LCD

Briefintroduction

Liquidcrystaldisplay(LCD)isatypeofdisplayusedindigitalwatchesandmanyportablecomputers.TheLCDdisplayusestwopiecesofpolarizedmaterial,betweenwhichisaliquidcrystalsolution.Whencurrentpassesthroughtheliquid,thecrystalsarerearrangedsothatlightcannotpassthroughthem.Therefore,eachcrystalislikeashutter,allowinglighttopassthroughandblockingit.Liquidcrystaldisplay(LCD)technologyinformationproductsarecurrentlydevelopingtowardsthegoalofbeinglight,thin,shortandsmall,anddisplayproductswithalonghistoryincomputerperipheralsareofcoursenoexception.Witheaseofcarryingandhandlingastheprerequisite,traditionaldisplaymethodssuchasCRTvideotubedisplaysandLEDdisplaypanelsaresubjecttofactorssuchasexcessivesizeorhugepowerconsumption,andcannotmeettheactualneedsofusers.Thedevelopmentofliquidcrystaldisplaytechnologyisinlinewiththecurrenttrendofinformationproducts.Whetheritisaright-angledisplay,lowpowerconsumption,smallsize,orzeroradiation,itcanallowuserstoenjoythebestvisualenvironment.

Thebirthofliquidcrystal

Totracetheoriginofliquidcrystaldisplays,wemustfirststartwiththebirthof"liquidcrystal".In1888AD,anAustrianbotanist,Friedrich.FriedrichReinitzerdiscoveredaspecialsubstance.Heextractedacompoundcalledhelicaltoluatefromplants.Duringheatingexperimentsonthiscompound,heunexpectedlydiscoveredthatthiscompoundhastwomeltingpointsatdifferenttemperatures.AnditsstateisbetweentheliquidandsolidsubstancesthatwegenerallyknowState,laternamedit"LiquidCrystal",whichmeansliquidcrystallinesubstance.However,althoughliquidcrystalswerediscoveredasearlyas1888,itwasonly80yearslaterwhentheywereactuallyusedindailynecessities.

In1968,attheSanovR&DCenterofRCA(theinventioncompanyofradioandtelevision),engineersfoundthatliquidcrystalmoleculeswouldbeaffectedbyvoltage,changingthearrangementoftheirmolecules,andcanThephenomenonofdeflectingtheincidentlight.Usingthisprinciple,RCAinventedtheworld'sfirstscreenusingliquidcrystaldisplay.Sincethen,liquidcrystaldisplaytechnologyhasbeenwidelyusedingeneralelectronicproducts,suchascalculators,electronicwatches,mobilephonescreens,instrumentsusedinhospitals(becauseofradiationmeasurementconsiderations)orscreensondigitalcameras,andsoon.Interestingly,thediscoveryofliquidcrystalswasearlierthanthatofvacuumtubesorcathoderaytubes,buttheworlddidn’tknowmuchaboutthisphenomenon.Itwasnotuntil1962thatthefirstbookwaspublishedbythechemistJoeoftheRCAresearchteam.ItisdescribedinabookpublishedbyMr.JoeCastellano.Similartotheimagetube,althoughthesetwotechnologieswereinventedbyRCAintheUnitedStates,theywerecarriedforwardbySonyandSharpinJapan.

Mainclassification

Accordingtothedrivingmode,liquidcrystaldisplayscanbeclassifiedintostaticdriving(Static),simplematrixdriving(SimpleMatrix)andactivematrixdriving(ActiveMatrix)..Amongthem,thepassivematrixtypecanbedividedintotwistednematic(TwistedNematic;TN),supertwistednematic(SuperTwistedNematic;STN)andotherpassivematrix-drivenliquidcrystaldisplays;andtheactivematrixtypecanberoughlydividedintoTherearetwomethods:ThinFilmTransistor(TFT)andTwo-terminaldiode(Metal/Insulator/Metal;MIM).

TN,STNandTFTtypeliquidcrystaldisplaysaredifferentinviewingangle,color,contrastandanimationdisplayqualitybecauseofthedifferenceintheprincipleoftwistingliquidcrystalmolecules,whichmakesthemintheproductapplicationrangeTheclassificationisalsoclearlyseparated.Intermsofthecurrentscopeandlevelofapplicationofliquidcrystaldisplaytechnology,theactivematrixdrivingtechnologyisbasedonthinfilmtransistortype(TFT)asthemainstream,andismostlyusedinnotebookcomputersandanimationandimageprocessingproducts.Thepurematrixdrivetechnologyiscurrentlybasedontwistednematic(TN)andsupertwistednematic(STN),andthecurrentapplicationsaremostlywordprocessorsandconsumerproducts.Amongthem,thecapitalinvestmentandtechnicalrequirementsrequiredforTFTliquidcrystaldisplaysarerelativelyhigh,whilethetechnicalandcapitalrequirementsrequiredforTNandSTNarerelativelylow.

Principleofoperation

Atpresent,mostliquidcrystaldisplaytechnologiesaremainlybasedonTN,STN,andTFT.Therefore,wewilldiscusstheiroperationprinciplesfromthesethreetechnologies.TNtypeliquidcrystaldisplaytechnologycanbesaidtobethemostbasicofliquidcrystaldisplays,andothertypesofliquidcrystaldisplayscanalsobesaidtobeimprovedbasedonTNtypeastheorigin.Similarly,itsoperatingprincipleissimplerthanothertechnologies.Pleaserefertothepicturebelow.ShowninFigure1isasimplestructurediagramofaTN-typeliquidcrystaldisplay,includingverticalandhorizontalpolarizingplates,alignmentfilmswithfinegrooves,liquidcrystalmaterials,andconductiveglasssubstrates.Theimagingprincipleistoplacetheliquidcrystalmaterialbetweentwopiecesoftransparentconductiveglassattachedtotheverticalpolarizingplateoftheopticalaxis.Theliquidcrystalmoleculeswillrotateinorderaccordingtothedirectionofthefinegroovesofthealignmentfilm.Iftheelectricfieldisnotformed,thelightwillbesmooth.Injectfromthepolarizer,rotatethedirectionoftravelaccordingtotheliquidcrystalmolecules,andthenshootoutfromtheotherside.Ifthetwopiecesofconductiveglassareenergized,anelectricfieldwillbecreatedbetweenthetwopiecesofglass,whichwillaffectthearrangementoftheliquidcrystalmoleculesbetweenthem,sothatthemolecularrodswillbetwisted,andthelightwillnotpenetrate,therebyshieldingthelightsource.Thephenomenonoflight-darkcontrastobtainedinthiswayiscalledthetwistednematicfieldeffect,orTNFE(twistednematicfieldeffect)forshort.Almostallliquidcrystaldisplaysusedinelectronicproductsaremadewiththeprincipleoftwistednematicfieldeffect.ThedisplayprincipleoftheSTNtypeissimilar.ThedifferenceisthattheliquidcrystalmoleculesoftheTNtwistednematicfieldeffectrotatetheincidentlightby90degrees,whiletheSTNsupertwistednematicfieldeffectrotatestheincidentlightby180to270degrees.WhatIwanttoexplainhereisthatapureTNliquidcrystaldisplayitselfhasonlytwomodesoflightanddark(orblackandwhite),andthereisnowaytoachievecolorchanges.TheSTNliquidcrystaldisplayinvolvestherelationshipbetweenliquidcrystalmaterialsandtheinterferenceoflight,sothecolortonesdisplayedaremainlylightgreenandorange.However,ifacolorfilterisaddedtothetraditionalmonochromeSTNliquidcrystaldisplay,andanypixel(pixel)ofthemonochromedisplaymatrixis​​dividedintothreesub-pixels(sub-pixel),thecolorfiltersarerespectivelytransmittedThefilmdisplaysthethreeprimarycolorsofred,greenandblue,andthenthroughthereconciliationoftheratiosofthethreeprimarycolors,thecolorsofthefull-colormodecanalsobedisplayed.Inaddition,iftheTNLCDdisplayscreenismadelarger,itsscreencontrastwillappearworse,butwiththeimprovedtechnologyofSTN,itcanmakeupforthelackofcontrast.

Liquidcrystaldisplay(3photos)

TFTtypeliquidcrystaldisplayismorecomplicated,themaincomponentsincludefluorescenttube,lightguideplate,polarizedlightPlates,filterplates,glasssubstrates,alignmentfilms,liquidcrystalmaterials,thinmodetransistors,etc.First,theliquidcrystaldisplaymustfirstuseabacklight,thatis,afluorescenttubetoprojectalightsource.Theselightsourcespassthroughapolarizingplateandthenthroughtheliquidcrystal.Atthistime,thearrangementoftheliquidcrystalmoleculeschangestheangleoflightpenetratingtheliquidcrystal.Thenthelightmustpassthroughthecoloredfilterfilmandanotherpolarizingplateinthefront.Therefore,wecancontrolthefinallightintensityandcolorbychangingthevoltagevaluethatstimulatestheliquidcrystal,andthencanchangethecolorcombinationofdifferentshadesontheliquidcrystalpanel.

Drivingmethod

InTNandSTNtypeliquidcrystaldisplays,themethodofusingsimpledrivingelectrodesisdrivenbythecrossmethodofXandYaxes,asshowninFigure2.Asshown,ifthedisplaypartgetsbiggerandbigger,thereactiontimeoftheelectrodeinthecenterpartmaybelonger.Inordertomakethescreendisplayconsistent,theoverallspeedwillbeslower.Toputitsimply,itseemsthatthescreenupdatefrequencyoftheCRTmonitorisnotfastenough,thatis,theuserwillfeelthescreenflickeringandjumping;orwhenfast3Danimationisrequired,thedisplayspeedofthemonitorcannotkeepup.Thekeyresultsdisplayedmaybedelayed.Therefore,theearlyliquidcrystaldisplayshavecertainlimitationsinsize,andtheyarenotsuitableforwatchingmoviesorplaying3Dgames.

Inordertoimprovethissituation,theliquidcrystaldisplaytechnologywaslaterdrivenbyactive-matrixaddressing,whichiscurrentlytheidealdevicetoachievehigh-data-densityliquidcrystaldisplayeffects,andtheresolutionExtremelyhigh.Themethodistousethesilicontransistorelectrodemadeofthinfilmtechnology,andusethescanningmethodtoselecttheonandoffofanydisplaypoint(pixel).Thisisactuallyusingthenon-linearfunctionofthethinfilmtransistortoreplacethenon-linearfunctionoftheliquidcrystalwhichisdifficulttocontrol.AsshowninFigure2,intheTFTtypeliquidcrystaldisplay,theconductiveglassisdrawnwithsmallnet-likelines,andtheelectrodesarematrixswitchesarrangedbythin-filmtransistors.Attheplacewhereeachlineintersects,thereisacontrolbox.Althoughthedrivingsignalquicklyscansthrougheachdisplaypoint,onlytheselecteddisplaypointinthetransistormatrixontheelectrodegetsenoughvoltagetodrivetheliquidcrystalmolecules,sothattheliquidcrystalmolecularaxisisturnedintoa"bright"contrast.Theselecteddisplaypointisnaturallythe"dark"contrast,thusavoidingthedependenceofthedisplayfunctionontheabilityoftheliquidcrystalelectricfieldeffect.