TFT-設(shè)計(jì)原理簡(jiǎn)介-0818-(NXPowerLite)

ArrayTFTpixeldesignIntroductionTFToperationandphysicsTFTarraydrivingtheoryandwaveformIssueforPixeldesignExample&SummaryIntroduction

LCDbasictheoryandstructureEquivalentpixelcircuit

我們一般在市面上看到的TFTLCD，若拆開看其橫截面結(jié)構(gòu)，如下圖：Introduction-TFTLCDpanel剖面圖

TFT_LCD面板主要可以拆解成3個(gè)部份，來說明：1.LCD面板:

2.TFT面板

3.背光板模組

至於其他一些DriverIC或是鐵框等，用以固定此3部份的結(jié)構(gòu)則不另敘述。

Introduction-LCDCrossSection

我們?nèi)舨豢幢彻獍迥＝M，而仔細(xì)觀察LCD面板和TFT面板組裝後的橫截面CFTFTIntroduction-ColorFilterR,G,B為一個(gè)pixel單一顏色為一個(gè)sub-pixeldpi=Pixel/inchIntroduction–ColordefinitionTotal#ofcolors#ofcolor=2(R)x2(G)x2(B)=2nnn3nN=#ofdatabitofLDIchip3bit=8-gray/RGB=512colors

4bit=16-gray/RGB=4,096colors

6bit=64-gray/RGB=262,144colors

8bit=256-gray/RGB=16,777,216colorsIntroduction-TFTPixel

控制流到ITOPixel區(qū)域的電荷量就可以決定了電場(chǎng)大小了

液晶會(huì)受到上下兩塊板子之間的電場(chǎng)大小所控制而變動(dòng)不同的垂直角度，電場(chǎng)愈大液晶改變的角度也愈大

TFTArray

ArrayMatrixGateline

SignallineTFTdevice

PixelGateICSourceICActive(Switch)(Scanline)(Dataline)Introduction-液晶顯像原理(TNmodenormallywhite)------PolarizerLiquidCrystalTFT面板LCD面板LightITO電極下偏光片上偏光片1.當(dāng)液晶站立起來時(shí)（和面板方向呈現(xiàn)90度）時(shí)，光線是不受液晶導(dǎo)引的。2.液晶站立的角度越垂直，越多的光不會(huì)被液晶導(dǎo)引，不同角度的液晶，其站立角度會(huì)導(dǎo)引不同數(shù)量的光線。以上面的例子來看，液晶站立角度越大，則可以穿透的光線越弱。（上、下偏光片排列的方向會(huì)決定穿透光的強(qiáng)弱，因此建議：只要了解液晶站立的角度會(huì)導(dǎo)光的強(qiáng)弱即可）不受導(dǎo)引的光線會(huì)被上偏光片所吸收掉。

(Fieldoff)(Fieldon)為何我們需要控制數(shù)百萬個(gè)pixel區(qū)內(nèi)液晶的角度呢？因?yàn)槲覀円靡壕У男庑詠砜刂乒饩€通過TFTLCD面板的強(qiáng)弱。

Introduction–equivalentcircuitofLCDV(data-n)V(Gate)V(P)V(Com)I(ds)C(LC)C(st)V(data-n+1)C(pd-L)C(pd-R)C(gs)*TFToperation

-Gate:activationofchannel

-S/D:currentpath

-Electrode:pixelcharging*Storagecapacitor

-Retainthechargeuntilasecond

signalisrecieved

-CsongateoronCom

-Cssizeandshape*LCcircuit

-asacapacitor

-asaninsulator:highresistivity

-minimizetheamountofimpurities

-responsetimeIntroduction-TFTturn-onM1SiNa-SiM2PVITO↑applypositivevoltage++++++++-------------sourcedraingatesourcedrainIntroduction-TFTturn-offM1SiNa-SiM2PVITO↑applynegativevoltage-----------+++++++++sourcedraingatesourcedrain

TFToperationandphysics

TFToperation

-Linearregion

-Saturationregion

-Kinkregion-SiTFTparameterdefinition

-On/Offstate

-Thresholdvoltage

-Mobility

-Sub-thresholdSwing

-ChannelW/Leffect

-Transfercurve(Id-Vg)

-Outputcurve(Id-Vd)

-DCvoltagestressing

-photo-currenteffect

TFToperationLinearregion

Saturationregion

Whatisthechannelwidthandchannellength?

TFToperation–LinearregionVG>VTHVD(SMALL)SN+N+CHANNELLIDDepletionRegion*InversionlayerformationIDVDTFToperation–SaturationregionVG>VTHVD=

VDsatSN+N+DepletionRegionIDPitch-OffPointIDIDsatVD*Pitch-offregionTFToperation–KinkregionVG>VTHVD>

VDsatSN+N+DepletionRegionIDPitch-OffPointIDVD*Kink-offorChannelmodulationVd>>(Vgs-Vth)-SiTFTparameter–definition

ON-State:IonatVd=5V/Vg=20V

-pixelcharging

Turn-ON:Vth

atIds=10^-9

-Trapstatedensity

&Si/SiNinterfacequality

-Vthshift~1V

Subthreshold:1/Slope

-Dependontrapdensity

Off-State:Ioff

atVd=5V/Vg=-15V

-leakagecurrent(holding)

On/Offratio:>10^6

Mobility:

-Gm=

Cox(W/L)Vds

-~0.3–1.9cm2/V.sec

-interfacescattering-SiTFTparameter–Transfercurve(ID-VG)OffCurrentRegionFittingSub-ThresholdRegionFittingOnCurrentRegionFitting-SiTFTparameter–Outputcurve(ID-VD)-SiTFTparameter–channel(W/L)effectW/L

W/L

-SiTFTparameter–DCstressPositivebiasstressNegativebiasstressChargeTrapping*InduceTrap-statesinInsulatorlayer-SiTFTparameter–photocurrent*A-Siissensitivetovisiblelightelectron-photoneffect:PhotocurrentTFTDrivingtheoryandWaveform

Drivingtheory

-V-TcurveofLCD

-TimingchartofLCD

-DrivingmethodWaveform

-Drivingwaveform

-Feed-thoughvoltage

-3-leveldriving

-CsequivalentcircuitDrivingtheory-

AddressingofTFTLCDDatalinesGate

linesFramerateandframetime

Displayresolution

Chargingtime

Storagecapacitor

HoldingvoltageSelect/unselectstateDrivingtheory-

V-TcurveofTFTLCD(TNmode)1000.010Transmittance(%)Voltage(BetweenVcom&Pixel)90VoltageBackLightLCPolarizerPolarizer90o

Drivingtheory-V-Tcurveofdirectdrivingscheme*DatalinevoltageatX-axis.*Thesignalisconvertedtoanalogfordifferentgrayleveloperation.*ToavoidchargingLC,thenegative/positiveinversionschemeisapplied.

Drivingtheory-timingchartofTFT-LCDFramerate:60Hz(frametime:1/60sec)

Gatepulse1/60/Nsec

ex:gate=1024lines;gatepulse=1/60/1024~16.3us

Drivingtheory-DrivingmethodFrameInversionLineInversionColumnInversionDotInversionDrivingtheory-FrameInversionGateinputDatainputVdata1Vdata2Vdata3VcomVdata1VcomVdata2VcomVdata3Gate1Gate2Gate3timeFramenFramen+11000.010Transmittance(%)90V,=Voltage(BetweenVcom&Pixel)VwVB

Gate1Gate2Gate3t1t2t3t4t5t6VB

VwGateinputDatainputVdata1Vdata2Vdata3Gate1Gate2Gate3timeFramenFramen+11000.010Transmittance(%)90V,=Voltage(BetweenVcom&Pixel)VwVB

Gate1Gate2Gate3t1t2t3t4t5t6VwVcomVdata1VcomVdata2VcomVdata3VB

+Thepolarityisdifferenttoneighbors+++_

Drivingtheory-DotInversionDrivingtheory-DrivingwaveformVcomVfVp=V+(正半周)Vp=V-(負(fù)半周)Vg:GateVf:feed-throughvoltageVd:DataTg(Ton)

Vh:duetoleakagecurrentVp:PixelDrivingtheory-whatisfeed-throughvoltage?On-state:Off-state:Chargeconservation:Inrealcase:Howtoproveit?VglVpixel(n)VcomVpixel(p)VghOffOnCgsClcCstCpd(next)Cpd(own)

Drivingtheory-WhengateturnonOffOnVglVpixel(n)VcomVpixel(p)VghClcCstCpd(next)Cpd(own)CgsClcCstCpd(own)CgsClcCstCpd(own)CgsFeedthroughVoltage

Drivingtheory-WhengateturnoffDrivingtheory-Feed-throughvoltageissue

Flicker:

ThevoltageappliedtoLCisdifferentbetweenpositiveandnegativeframes

-Itwilllead30Hzflicker(humanvisualretention~30ms)-DependenceofVft

-IndirectlyaffectImageStickingMuraissue:Causedifferentgray-levelinlocalareaofpanel

-Mosthappen:V-bandmura,H-bandmura,…etc.

-DependenceofVft

Howtoreduceit?LowerVft,betterperformance

-3-leveldrivingcompensation(onlyforCsongate)

-ReduceTFTarea(Trade-off:Iondown)

-IncreaseCsarea(Trade-off:A.Rdown)Drivingtheory-3-leveldriving經(jīng)Cgs

的Feed-through電壓

=(Vgh–Vge)×Cgs/(Cgs+Clc+Cs)

經(jīng)Cs的Feedthrough電壓

=(Vge-Vg1)×Cs/(Cgd+Clc+Cs)

VghVglVge

Vge=(Vgh-Vgl)×Cgs/(Cs–Cgs)

Drivingtheory-CsequivalentcircuitsDrivingtheory-Csoncomv.sCsonGate

Csongate

*Csongateline

A.Rup

gateRCloadingbig

Cssmall

*VftcompensationA.Rup(Csdoesn’tneedlarge)

*ComplicatedriverICdesignCostup

*H-comdesignA.Rup

Csoncommon

*IndependencecomlineA.Rdown

gateRCloadingsmall

Cslarge(MIMstructure)

*VftreduceA.Rdown(LargeCsinneed)

Issueforpixeldesign

Apertureratio:BMdesignIonissue:chargingratioIoffissue:holdingvoltageRCdelay:gate-line/data-lineFeed-throughvoltage:Cgs/Ctotal,CgscompensationFlicker:Cgs/CtotalCoupling:Cpd

coulingCsdesign:type,areaProcesswindow:ASM,ArrayOLshift,Ionuniformity

Issueforpixeldesign-AperturesizePixelsizedetermination

-Panelsize

-ResolutionApertureratio

-BMareaA.R:

Pixeltotalarea–areaof(gate+data–crossover+TFT+Vcom)–

BMcoverareaIssueforpixeldesign–PixelelementsCstCgsCgdCpdCpd’Cgd’ScanlineScanlineDatalineDatalineClcTFTVpixelVcomCgcfVcomlineIssueforpixeldesign–PixelchargingChargingratio=V(6)/V(2)x100%

Generally>99%

NeedtoconsiderRCdelay&processwindow*BaseonproperI-Vcurve:

UseLCDdoctororSmart/AIMSpicetosimulateIssueforpixeldesign–Pixelholding*TomaintainthepixelvoltagewhiletheTFTisoff

-TFTleakagecurrent(Ioff)

-LCimpurity

-GIleakage(Igs)Chargingtimeconstant:

Experiencedsetting:

Holdingtimeconstant:

Voltageholdingratio:

Issueforpixeldesign–RCdelay

VftuniformityChargingshortageCross-talk(nextsignal)Badpanelquality:Improvemethods:ReduceR&CofGatelineGateshapingIssueforpixeldesign–Cpdcoupling

Cross-talk:

-data-linesignalscoupletopixelvoltage

-Horizontalelectricfield(affectLCdirection)Muraissue:Causedifferentgray-levelinlocalareaofpanelHowtoreduceit?LowerCpd,betterperformance

-Data-linetoITOpixeldistance(Trade-off:A.Rdown)

-BMcoverITO(Trade-off:A.Rdown)

-IncreaseCsarea(Trade-off:A.Rdown)CpdCpd’

Issueforpixeldesign–Cross-talk(On-state)VglVpixel(n)VcomVpixel(p)VghOffOnCgsClcCstCpd(next)Cpd(own)CstClcCgsCpdCpd’FrameInversion:Cpd&Cpd’coupletosamedatapotentialIssueforpixeldesign–Cross-talk(Off-state)OffOnCpd(next)VglVpixel(n)VcomVpixel(p)VghClcCstCpd(own)ClcCstCpd(own)CgsClcCstCpd(own)CgsFeedthroughVoltageClcCstCpd(own)CgsClcCstCpd(own)CgsCstClcCgsCpdCpd’FrameInversion:Can’tbalanceCpd

differencebythepolaritychange!PositionAPositiveFramePositiveFrameNegativeFramePositionBPositiveFramePositiveFrameNegativeFrameUnderFrameInversionIssueforpixeldesign–Cross-talk(example)BAChargingChargingChargingCpdcouplingCpdcouplingCpdcouplingCstClcCgsCpdCpd’Issueforpixeldesign–Cross-talk(example)BAA1A2B1B2PositiveFramePositiveFrameNegativeFrameUnderFrameInversionA1A2B1B2Vp

RMSA1>B1~B2>A2CstClcCgsCpdCpd’

Summary

Example

-Spicesimulation

-Feed-throughvoltagesimulation

Pixeldesignflow

-Algorithrm

-Designspec&requiredparameters

-Designparameters&output

ConcernItemExample–AIMsimulation:Devicemodelextraction1.TEGdataanalysisAboveThresholdBelowThresholdHole-InducedLeakageCurrentExtractParameterExample–AIMsimulation:DevicemodelextractionModeledMeasuredIdVdCurveVg=5V,10V,15V,20V,30VIdVgCurveVd=1V,4V,7V,10V2.CurvefittingBuildmodelcardExample–Pixelequivalentcircuit&RCcalculationCgate=((Cst*Clc)/(Cst+Clc)+Cgs+Cgs_coup

+Cdgcross+Cgate_com)*1280*3Rgate=(ρ*L1/W1)*1280*3Cdata=(Cgd+Cdgcross+Cdata_com+Cpixel_data_coup)*1024Rdata=(ρ*L2/W2)*1024Cpixel=Cgs+Cgs_coup+Clc+Cst+Cpixel_data_coupGateLinetheNthGateLinethe(N-1)thDataLinetheN-1thDataLinetheNthC

gsC

gdC

st(ongate)C

lcCpixel_datacoup(next)Cpixel_datacoup(own)C

gs_coupCdgcrossCdata_com(lc)Cgate_com

12345679810Pi-circuittosimplify3.RCcalculateExample–Spicesimulate4.RunSpiceWhatcanwegainfromthisWaveformChart?

GateDelay

ChargingCapabilityFeedthroughVoltageExample–Feed-throughvoltagesimulationInput-MeasurementdataCgs各項(xiàng)參數(shù)Cgs-onCgs-offCalculateCalculateOutput-V變化

正半週Vft負(fù)半週Vft

VcomExample–Cgsareadefinition:On-stateCgsCgsExample–Cgsareadefinition:Off-stateExample–inputparameters&formulaCapacitance:Vg&Vsig:Example–Output&processwindowDesignflow–AlgorithmSalesTarget

-Spec.(resolution…)

-Quantity

-SchedulePixelDesign

TFTdesign(W/L,gatewidth…)

Designpara.(Cgs,chargingratio…)

Layouttype(H-type,Csongate…)

Peripherallayout(fanout,rescueline…)Arraydesign

-processpara.(THK,CDbias…)

-processwindow