TFT-设计原理简介-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構，如下圖：Introduction-TFTLCDpanel剖面圖

TFT_LCD面板主要可以拆解成3個部份，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部份的結構則不另敘述。

Introduction-LCDCrossSection

我們若不看背光板模組，而仔細觀察LCD面板和TFT面板組裝後的橫截面CFTFTIntroduction-ColorFilterR,G,B為一個pixel單一顏色為一個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區域的電荷量就可以決定了電場大小了

液晶會受到上下兩塊板子之間的電場大小所控制而變動不同的垂直角度，電場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.當液晶站立起來時（和面板方向呈現90度）時，光線是不受液晶導引的。2.液晶站立的角度越垂直，越多的光不會被液晶導引，不同角度的液晶，其站立角度會導引不同數量的光線。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決定穿透光的強弱，因此建議：只要了解液晶站立的角度會導光的強弱即可）不受導引的光線會被上偏光片所吸收掉。

(Fieldoff)(Fieldon)為何我們需要控制數百萬個pixel區內液晶的角度呢？因為我們要利用液晶的旋光性來控制光線通過TFTLCD面板的強弱。

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Cgs

的Feed-through電壓

=(Vgh–Vge)×Cgs/(Cgs+Clc+Cs)

經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各項參數Cgs-onCgs-offCalculateCalculateOutput-V變化

正半週Vft負半週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