zn 기반 산화물 트랜지스터 소자의 이해 및 연구 현황 -...

Zn 기반 산화물 트랜지스터 소자의

이해 및 연구 현황

Zn 기반 산화물 트랜지스터 소자의

이해 및 연구 현황

인하대학교 신소재공학과정재경

인하대학교 신소재공학과정재경

KRICT 세미나2009.12.10. 13:30-15:00

KRICT 세미나2009.12.10. 13:30-15:00

True Leader in Digital WorldSamsung SDI

INTRODUCTION

RESULTS & DISCUSSIONS

CONCLUSIONS

Contents Contents

AMOLED development & production status

Why oxide TFT? Development status of Oxide TFT

Degradation mechanism of Oxide TFTsR&D status of soluble oxide TFT

Summary

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True Leader in Digital WorldSamsung SDIAMOLED R&D & Production Status AMOLED R&D & Production Status

2003

SDI (’03. 05)15.5” WXGA

Seiko-Epson(’04.4)12.5”VGA(64ppi)

2004

SDI (’04.11)17” UXGA SGS

SEC(’05.1)21”WUXGA(105ppi)

LG 20.1” (’04.12) XGA

2.16” SKD(’03. 4)

3.8” SONY(’04 .9)

2006 20072005

SEC(’05.5)40”WXGA(106ppi)

SONY(’07.1)27” FHD

2008■■

2.2” SDI(’07 6) 2~3” SDI

(’07.11)

4” SDI(’08.1)

11” Sony(’07.12)

SDI(’08.1)32” FHD

■ ■■ ■ ■ ■ ■

CMEL(’07.10)25” WXGA

■ ■■ ■ ■ ■ ■

Prod

uctio

nD

evel

opm

ent

Rapid progress of large Area AMOLED for TV applicationAdvantage of large AMOED : Vivid moving picture, Low power, Ultra Slim & unique value.

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Stability

Scal

abili

ty, U

nifo

rmity

Research Motivation of Oxide TFTResearch Motivation of Oxide TFT

Amorphous Si TFT(Gen.10)

40” AMOLED TV, SID 06” (SEC)

ELA based poly Si TFT (Gen.4)

31” AMOLED TV, CES’08 (SDI)

Amorphous structureInherently stable materialUse conventional equipment

Amorphous structureInherently stable materialUse conventional equipment

Can current technologies meet the requirements?need new uniform, scalable and stable TFTs.

ImageImage

High StableHigh performanceNon uniform Scalability

ScalableUniformLow mobilityReliability IssueSensitive to light & Temp.

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poly-Si TFT a-Si TFT Oxide TFTSemiconductor Polycrystalline Si Amorphous Si Amorphous IGZOTFT uniformity Poor Good GoodPixel Circuit Complex (5T+2C) Complex (4T+2C) Simple (2T+ 1C)

Channel Mobility ~100 cm2/Vs 1cm2/Vs 10 ~ 40 cm2/VsCircuit Integration YES NO YES

Reliability (@IDS=3uA,30khr) ∆Vth < 0.5V ∆Vth >30V ∆Vth ~ 1.7VTFT Type PMOS(CMOS) NMOS NMOS

TFT Mask Steps 5~11 4~5 4~5Cost/Yield High/low Low/high Low/high

Process Temperature 450~550oC 150~350oC 150~350oC

Device Merits•Temp. Stability•High reliability

•High Uniformity •No Kink •No hot carrier effect•Low Ioff

Process/Scalability

• No Crystallization • No ion doping

(Ultra low cost)

Comparison of TFT PropertiesComparison of TFT Properties

Photolithography PECVDSputterDry EtcherELAIon ShowerFurnace

Photolithography PECVDSputterDry Etcher

Photolithography PECVDSputterDry Etcher

>Gen. 8>Gen. 8>Gen. 8

Gen. 4Gen. 4Gen. 4

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True Leader in Digital WorldSamsung SDIR&D History of Oxide TFTsR&D History of Oxide TFTs

2004

1.4” AMLCDCasio

2006 20072005 2009■ ■■■ ■■ ■ ■

Prot

otyp

e

2008 ■

IGZO TFTHosono GrNature

2.2” T-AMOLEDETRI

2” E-paperToppan

3.5” AMOLEDLGE

4.1” T-AMOLEDSamsung SDI

3.5” F-AMOLEDLGE

4” E-paperToppan

12.1” AMOLEDSamsung SDI

2.2” T-AMOLEDETRI

15” AMLCDSEC

6.5” F-AMOLEDSamsung SDI

2.2” T-AMOLEDETRI

4” AMLCDSEL

2.2” AMOLEDSAIT

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SID2007, “Distinguished Paper”Top emission AMOLED

LGE AMOLED & Flexible Display (2007)LGE AMOLED & Flexible Display (2007)

3.5” QCIF AMOLED

Items SpecificationDiagonal size 3.5 inchNo. of pixels 176 x 220

Sub pixel pitch 215 x 235 µm2

Pixel element 2Tr 1CapOLED Top Emission

Substrate Stainless steel

3.5” Flexible AMOLED

IMID2007, 원천기술대상Top emission AMOLED

Transfer Characteristics

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Items SpecificationDiagonal size 12.1 inch

No. of pixels 1280 x RGB x 768

Sub pixel pitch 69 x 207 µm2

Resolution 123 ppi

Panel size 283 x 181 mm2

Pixel element 2Tr 1CapGray 256 gray

Scan driver Integration

OLED Bottom EmissionNormal Structure

Color coordinate

White (0.31, 0.31)Red (0.67, 0.33)

Green (0.29, 0.64)Blue (0.15, 0.11)

12.1” WXGA

The largest AMOLED driven by oxide TFTs array.The largest AMOLED driven by oxide TFTs array.

Samsung SDI AMOLED (2008)Samsung SDI AMOLED (2008)

References: JSID, 17, 95 (2009)

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True Leader in Digital WorldSamsung SDISamsung Electronic TFT-LCD (2008)Samsung Electronic TFT-LCD (2008)

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True Leader in Digital WorldSamsung SDISamsung Electronic TFT-LCD (2008)Samsung Electronic TFT-LCD (2008)

Lee et al., SID digest 42-2 p.25 (2008)

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True Leader in Digital WorldSamsung SDIOptimized Transistor PerformanceOptimized Transistor Performance

• Field-effect mobility = 20.1cm2/Vs• S-factor = 0.28 V/decade• Ion/off = 1E9• Vth,sat = 1.8V

• Field-effect mobility = 20.1cm2/Vs• S-factor = 0.28 V/decade• Ion/off = 1E9• Vth,sat = 1.8V

Device characteristicsDevice characteristicsDevice structureDevice structure

• Bottom Gate + ESL • DC Sputtered IGZO• Wet/Dry etching process• Metal Gate & S/D

• Bottom Gate + ESL • DC Sputtered IGZO• Wet/Dry etching process• Metal Gate & S/D

MoBuffer

Glass substrate

SiOx/SiNx

IGZOMo

SiOx

-20 -10 0 10 20 301x10-141x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-41x10-3

VDS=0.1V VDS=5.1V

I DS (

A)

VGS (V)

Reference: Information Display 9, 20 (2008).

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True Leader in Digital WorldSamsung SDIMerit 1: Uniformity of Oxide TFTsMerit 1: Uniformity of Oxide TFTs

Mobility (cm2/Vs)

STD of mobility(V)

Vth (V)

STD of Vth (V)

Oxide (LRU) 10.8 0.55 2.5 ~0.11(similar to ELA)Oxide (SRU) 10.5 0.46 1.8 < 0.01(much better than ELA)LTPS (SRU) 102.4 3.69 1.5 ~ 0.11

-20 -10 0 10 20 301x10-141x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-4

Dra

in c

urre

nt (A

)

Gate voltage (V)

TFT Properties UniformityTFT Properties Uniformity

• Short range uniform is excellent due to amorphous property of IGZO layer.

• Contact resistance uniformity is a more critical factor.

• Long range uniformity is depends on IR drop of electrode lines.

• Short range uniform is excellent due to amorphous property of IGZO layer.

• Contact resistance uniformity is a more critical factor.

• Long range uniformity is depends on IR drop of electrode lines. 9points overlap

Within Gen. 2

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-15 -10 -5 0 5 10 1510-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

0 1 2 310-13

10-11

10-9

10-7

10-5

Dra

in C

urre

nt [A

]

Gate Voltage [V]

Vds initial 10V 15V 20V

-20 -15 -10 -5 0 5 10 15 20 25 3010-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

0 1 2 3 4 510-13

10-11

10-9

10-7

10-5

Dra

in C

urre

nt [A

]

Gate Voltage [V]

Vds initial 10V 15V 20V

• Transfer curves: Vds=5.1V• Stress condition: Vg=Vth+0.5V; Vds=10,15, 20V; 300sec • Transfer curves: Vds=5.1V• Stress condition: Vg=Vth+0.5V; Vds=10,15, 20V; 300sec

n-typewith ESLW/L=7/7um

n-typewith ESLW/L=7/7um

n-typeLDD=2umW/L=7/7um

n-typeLDD=2umW/L=7/7um

ELA LTPS TFTELA LTPS TFT

0 5 10 15 200

20

40

60

80

100 ELA 4/4 um ELA 7/7 um Oxide 7/7 um Oxide 25/10um

Lin.

Mob

ility

[cm

2 /V.s

]

Stress S/D Bias [V]

Mobility variationsMobility variations

ELA (7/7 um)

Oxide (7/7 um)

∆U,lin/U,init @ Vds=15V -70.4% +3.0%

∆Ion/Ion,init @ Vds=15V -48.6% -9.4%

Merit 2: Hot Carrier EffectMerit 2: Hot Carrier Effect

Oxide TFTOxide TFT

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0 2 4 6 8 10 120

2x10-8

4x10-8

6x10-8

8x10-8

1x10-7

1x10-7

1x10-7

VDS=0.1V VDS=1.1V VDS=2.1V VDS=3.1V

I ds(A

)

VDS(V)0 2 4 6 8 10 12

01x10-62x10-63x10-64x10-65x10-66x10-67x10-68x10-69x10-6

VDS=0.1V VDS=1.1V VDS=2.1V VDS=3.1V

I ds(A

)

VDS(V)

• Tested TFT: W/L=7/7um, Vgs=0.1~3.1V• GIZO TFT: No Kink effect (Negligible hot carrier effect) presumably due to wide band-gap and amorphous phase nature of IGZO semiconductor layer

• Tested TFT: W/L=7/7um, Vgs=0.1~3.1V• GIZO TFT: No Kink effect (Negligible hot carrier effect) presumably due to wide band-gap and amorphous phase nature of IGZO semiconductor layer

Merit 3: Kink EffectMerit 3: Kink Effect

ELA LTPS TFTELA LTPS TFT Oxide TFTOxide TFT

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-15 -10 -5 0 5 10 151x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-41x10-3

Before stress 600 sec 1Hr 2Hr 3Hr 6Hr 10Hr

I ds(A

)

VDS(V)

△Vth=0.13V

Vds=5.1V

-20 -10 0 10 20 301x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-41x10-3

Before stress 600 sec 1 Hr 2 Hr 3 Hr 6 Hr 10 Hr

I ds(A

)

VGS(V)

△Vth=2.36V

Vds=5.1V

LPTS Vth,sat(V)

Mobility(cm2/Vs)

Ion(uA/um)

SS (V/dec)

Before 1.46 99.8 14.9 0.22

After 1.59 56.7 11.8 0.28

Oxide Vth,sat(V)

Mobility(cm2/Vs)

Ion(uA/um)

SS (V/dec)

Before 1.11 8.20 0.60 0.58

After 3.47 8.60 0.37 0.62

Issue 1: DC StabilityIssue 1: DC Stability

• Stress condition: Ids=10uA, time = 10hr (severe condition)• The DC stability of Oxide TFT should be improved !!!! How??• Stress condition: Ids=10uA, time = 10hr (severe condition)• The DC stability of Oxide TFT should be improved !!!! How??

ELA LTPS TFTELA LTPS TFT Oxide TFTOxide TFT

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• W/L=7/7um TFT • In case of GIZO TFT, serious temperature dependence (>40C)

Inherent property of a-IGZO material or influenced by process???

• W/L=7/7um TFT • In case of GIZO TFT, serious temperature dependence (>40C)

Inherent property of a-IGZO material or influenced by process???

-15 -10 -5 0 5 10 151x10-141x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-41x10-3

-40oC -20oC 0oC 20oC 40oC 60oC 80oC 100oC

I DS(

A)

VGS(V)-15 -10 -5 0 5 10 151x10-14

1x10-131x10-121x10-111x10-101x10-91x10-81x10-71x10-61x10-51x10-41x10-3

-40oC -20oC 0oC 20oC 40oC 60oC 80oC 100oC

I DS(

A)

VGS(V)

Vds=5.1VVds=5.1V

Issue 2: Temperature stabilityIssue 2: Temperature stabilityELA LTPS TFTELA LTPS TFT Oxide TFTOxide TFT

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-40 -20 0 20 401x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

I DS (

A)

VGS (V)

RT 40C 60C 80C 100C

Vds=5.1V Vds=5.1V

-40 -20 0 20 401x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

I DS (

A)

VGS (V)

RT 40C 60C 80C 100C

-40 -20 0 20 401x10-12

1x10-11

1x10-10

1x10-9

1x10-8

1x10-7

1x10-6

1x10-5

1x10-4

1x10-3

I DS (

A)

VGS (V)

RT 40C 60C 80C 100C

Vds=5.1V

FMM W/O ESL FMM Conventional ESL Advanced ESL

Solution to Temperature StabilitySolution to Temperature Stability

• Not IGZO oxide TFT issue• Not Etching process but deposition process• New ESL material improve the temperature stability dramatically

• Not IGZO oxide TFT issue• Not Etching process but deposition process• New ESL material improve the temperature stability dramatically

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True Leader in Digital WorldSamsung SDIPotential Mechanisms of Vth Instability Potential Mechanisms of Vth Instability

β

β

τ

1

)(−

∝∝ttN

dtdN

dtdV

ftrth

Vth shift : “charge trapping-related”

oxtrth CeNV /=∆

Nf: free-carrier densityτ: time constantβ: dispersion parameter(T/T0)

EC

EV

EF

Ei

e`-

e-e-

e-

e-

1) charge trapping

2) charge injection

3) Channel degradation

4) back channel: O2, H2O, H2 ads/des

Band diagram (VBand diagram (VGSGS > 0)> 0)

Metal

Insulator

Semiconductor

]})(exp[1{)( 0β

τtVtVth −−=∆

where 0,0 thg VVV −=

)exp(1

kTEa−=ντ

Ea: activation erg of trapping

ν: frequency pre-factor

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True Leader in Digital WorldSamsung SDI1st Report Regarding Vth Instability of ZnO TFT1st Report Regarding Vth Instability of ZnO TFT

virgin

40V stress

Recovery @ room temp

• The evaluated device was not passivated, which means that the back surfaceis exposed into ambient atmosphere

• The evaluated device was not passivated, which means that the back surfaceis exposed into ambient atmosphere

Vth recovery at room temperature : charge trapping at GI/active(injection; high de-trapping barrier

Vth recovery at room temperature : charge trapping at GI/active(injection; high de-trapping barrier

Cross et al. APL 89, 263513 (2006)De Montfort Univ. Group

• Positive stress : Vth + shift : charge trapping or injection

• Positive stress : Vth + shift : charge trapping or injection

PBTI and Recovery of ZnO TFT PBTI and Recovery of ZnO TFT

EC

EV

EF

Eie`-

e-e-

e-

e-

Insulator

Semiconductor

19/56

True Leader in Digital WorldSamsung SDICharge Injection Model (IGZO TFT)Charge Injection Model (IGZO TFT)

Suresh et al. APL 92, 033502 (2008) NCSU Group

• Limitation: IGZO transistor without any passivation layer ??- The effect of ambient can be included, which results in the misleading

interpretation.

• Limitation: IGZO transistor without any passivation layer ??- The effect of ambient can be included, which results in the misleading

interpretation.

PBTI of IGZO TFTPBTI of IGZO TFToxth CtQtV /)()( =∆

)log()(0

0 ttrtVth =∆

∫ ∫ −=t x

tr txxNdxdttQ0 0

''''' ])(exp[)()( ϖϖ

Ntr: traps density in dielectric

ϖ(x): tunneling probability

EC

EV

EF

Ei

e`-

e-e-

e-

e-

Insulator

Semiconductor

20/56

True Leader in Digital WorldSamsung SDIAmbient Effect on Stability (1)Ambient Effect on Stability (1)

Concept modelConcept model

•ZnO is “oxygen sensor”:adsorption → conductivity ↓

•O2 adsorption on IGZO Transistor:Vth positive shift (SAIT, APL2007)

O2 ads/desorption O2 ads/desorption

)(2)(2 solidOegasO −− =+

a-IGZO

Oxygen (O2)

e-

δ-

a-IGZO

→ Channel depletion→ Conductivity ↓→ Vth positive shift

O2 adsorption on ZnO

][/][ 2 nPOK Osolid−=

In vacuum, if PO2 ↓, [O-]solid ↓ (K is invariant)

→ O2 desorption → Vth negative shift

If PO2 ↑, [O-]solid ↑ (K is invariant)

→ O2 adsorption → Vth positive shift

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True Leader in Digital WorldSamsung SDIAmbient Effect on Stability (2)Ambient Effect on Stability (2)

101 102 103 104

0.0

0.5

1.0

1.5

2.0 W/O passi LT SiO2 HT SiO2

∆V th

(V)

Stress time (Sec)

a-IGZO

Oxygen (O2)

e- e- e- e-

δ- δ- δ- δ-

Gate

Dielectric

VGS > 0

- - - -

Field-induced adsorption

- ---a-IGZO

+ + + ++ + + ++ +

Concept of fieldConcept of field--induced induced ∆∆VVthth

)(2)(2 solidOegasO −− =+

][/][ 2 nPOK Osolid−=

During on-state stress (VGS > 0), n ≈ Cgate(VGS-Vth)↑

∴ [O-]solid ↑ (K is invariant)

→ O2 adsorption (field-induced) → Vth positive shift

In case of H2O(OH-), when VGS > 0,

→ H2O(OH-) desorption → Vth positive shift

Reference: APL, 93, 123508 (2008).

)()log(]})(exp[1{)(0

00 tVttrtVtV ambientth ++−−=∆∴ β

τ

MoW S

SiNxD

W/O passi

MoW SiNx

IGZO (50nm)SiOx

SiO2 passi

e-

δ-

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True Leader in Digital WorldSamsung SDICritical Factors Affecting Stability

Hi (OH)e

UV

>150 oC

Source Drain

50 nm

O- O-

e e

O- O-

e e

Conductive Layer

H2OH2O

H2O

β

β

τ

1

)(−

∝∝ttN

dtdN

dtdV

ftrth

Ntr change due to ambient interaction such as O2, H2O, H2 etc

Species No field Positive stress Negative stress

O2Acceptor

(Vth ↑) More adsorption

(Vth ↑)More desorption

(Vth ↓)

H2ODonor (Vth ↓)

More desorption (Vth ↑)

More adsorption (Vth ↓)

H2Donor (Vth ↓)

More desorption (Vth ↑)

More adsorption (Vth ↓)

Concept of Electrical-field-induced Vth shift

Reference: APL, 92, 072104 (2008). 23/56

True Leader in Digital WorldSamsung SDIImpact of Device Structure on StabilityImpact of Device Structure on Stability

Unpassivated BG structure

SiOx

Glass substrate

ITO ITO

AZITOAl2O3

(a)

Passivated BG structure

• The channel materials is AZITO not IGZO • Passivation layer is ALD-derived Al2O3 thin film• The channel materials is AZITO not IGZO • Passivation layer is ALD-derived Al2O3 thin film

SiOx

Glass substrate

ITO ITO

AZITOAl2O3

Al2O3AlOx

Reference: APL, 95, 123505 (2009).IEEE EDL (in press)

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-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4

VDS = 0.5V VDS = 15.5V

I DS (A

)

VGS (V)-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4

VDS = 0.5V VDS = 15.5V

I DS (A

)

VGS (V)

Bottom gate structure w/o passivation

Bottom gate structure w passivation

Impact of Device Structure on StabilityImpact of Device Structure on Stability

ID Mobility (cm2/Vs) SS Ion/off Vth (V)Unpassivated BG 32.4 0.13 2× 109 -1.5

Passivated BG 31.9 0.07 2× 109 -0.2

Reference: IEEE EDL (in press)

25/56


-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4I D

S (A)

VGS (V)

25 oC 50 oC 75 oC 100 oC 125 0C

-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4

I DS (A

)

VGS (V)

25 oC 50 oC 75 oC 100 oC 125 0C

(a) (b)

-2 0 2 4 6 8 10 12 140.00.40.81.21.62.02.42.8

E a (eV

)

VGS (V)

W/L = 20/5 µm 20/10 µm 20/20 µm 20/40 µm 40/20 µm

0 2 4 6 8 10 120.0

0.2

0.4

0.6

0.8

1.0

1.2

E a (eV

)

VGS (V)

W/L = 20/5 µm 20/10 µm 20/20 µm 20/40 µm 40/20 µm

(c) (d)

Temperature-dependent InstabilityTemperature-dependent InstabilityUnpassivated device Passivated device


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True Leader in Digital WorldSamsung SDIEF variation as a f’n of gate voltageEF variation as a f’n of gate voltage

Plot of activation energy and VGS

AssumptionSub-threshold current is due to the excitation of electron at DOS into conduction band and subsequent driftc

EC

EV

EF

Ei

e`-

e-

e-

e-

MetalInsulator

Semiconductor

EA =EC -EF

)(1

FSSGS

F

GS

A

ENdVdE

dVdE

∝∝

FSSGSi ENVC ∆≈Q

InterpretationThe change rate of EF wrt VGS is inversely proportional to Nss(EF) or DOS(EF)Rapid change of EA for TG TFT means less DOS of the channel layer or/and Dit compared to BG TFT w/o passivation

-1 0 1 2 3 4 5 6 7 80.0

0.4

0.8

1.2

1.6

2.0

Top gate Bottom gate

Act

ivat

ion

ener

gy (e

V)

VGS (V)

27/56


-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4

I DS (

A)

VGS (V)

0 s 3,000 s 10,000 s 36,000 s

-8 -4 0 4 8 1210-14

10-12

10-10

10-8

10-6

10-4

I DS (

A)

VGS (V)

0 s 3,000 s 10,000 s 36,000 s

Effect of Passivation on DC stability

Stress condition:VGS = 20V, VDS=0VDuration= 36,000 sec

Unpassivated device Passivated device

• Unpassivated device : 1.8V shift from -1.5V to 0.3V• Passivated device: only 0.2V shift • This result can be explained by the prevention of the ambient effect.

• Unpassivated device : 1.8V shift from -1.5V to 0.3V• Passivated device: only 0.2V shift • This result can be explained by the prevention of the ambient effect.


28/56


-30 -25 -20 -15 -10 -5 0 5 10 1510-1410-1310-1210-1110-1010-910-810-710-610-510-410-3

10-1410-1310-1210-1110-1010-910-810-710-610-510-410-3

I DS

(A)

VGS (V)

before after

I G (A

)

-10 -5 0 5 10 1510-1410-1310-1210-1110-1010-910-810-710-610-510-410-3

10-1410-1310-1210-1110-1010-910-810-710-610-510-410-3

I DS

(A)

VGS (V)

before after

Humidity test: 1day exposure to RH 100% ambientHumidity test: 1day exposure to RH 100% ambient

W/O passi. With AlOx passi.

w/o passi with AlO passi.ΔVT 10.7 V <0.1 V

Humidity Dependence

Unpassivated device Passivated device

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True Leader in Digital WorldSamsung SDIProposed Passivated TFT Structure Proposed Passivated TFT Structure

Studied device

(b)

Glass

ITOAl2O3

ITOITO

Al2O3

ZnInSnOAl2O3

1) Prevention of passivation damage2) Or subsequent patterning-induced attack1) Prevention of passivation damage2) Or subsequent patterning-induced attack

unambiguous interpretation of stability degradation mechanism

unambiguous interpretation of stability degradation mechanism

Advantage of Al2O3-protected channel structureAdvantage of Al2O3-protected channel structure

1) Excellent barrier property against water or oxygen diffusion

1) Excellent barrier property against water or oxygen diffusion

Advantage of ALD-Al2O3 passivationAdvantage of ALD-Al2O3 passivation

Session 26. 4 M. K. Ryu et al. “Highly stable Zn-In-Sn-O TFTs for the application of AM-OLED”

References: APL, 95, 173508 (2009),APL, 95, 072104 (2009)

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True Leader in Digital WorldSamsung SDIPBTI of ZIT TFTs with Good Passivation

confidential

-5 -4 -3 -2 -1 0 1 2 3 4 510-1310-1210-1110-1010-910-810-710-610-5

I DS

(A)

VGS (V)

0s 30s 100s 300s 1ks 3ks 7.2ks 10ks

-5 -4 -3 -2 -1 0 1 2 3 4 510-1310-1210-1110-1010-910-810-710-610-5

I D

S (A

)

VGS (V)

0s 30s 100s 300s 1ks 3ks 7.2ks 10ks

The composition effect on the stability of ZnInSnO TFTThe composition effect on the stability of ZnInSnO TFT

(c) DeviceMobility : >24cm2/VsGate swing: 0.11V/decadeIon/off ratio > 1E9

Stress condition:VGS = 10V, VDS=0VDuration= 104 sec

ASn:Zn=30:50

BSn:Zn=35:45

-5 -4 -3 -2 -1 0 1 2 3 4 510-1310-1210-1110-1010-910-810-710-610-5

I DS

(A)

VGS (V)

0s 30s 100s 300s 1ks 3ks 7.2ks 10ks

CSn:Zn=40:40

101 102 103 104

0.0

0.1

0.2

0.3

0.4

0.5

-0.2

-0.1

0.0

0.1

0.2

∆SS

(V/d

ecad

e)

∆V

th (V

)

Stress time (sec)

Device A Device B Device C

0.17V

TrapCreation !!!

ChargeTrapping !!!

No change !!!

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confidentialTemperature instability of ZIT TFTs

-5 -4 -3 -2 -1 0 1 2 3 4 510-14

10-12

10-10

10-8

10-6

10-4

298K 323K 348K 373K 398K

I DS

(A)

VGS (V)-5 -4 -3 -2 -1 0 1 2 3 4 510-14

10-12

10-10

10-8

10-6

10-4

298K 323K 348K 373K 398K

I DS

(A)

VGS (V)

Evolution of the transfer characteristics with increasing temperatureEvolution of the transfer characteristics with increasing temperature

The stability of Device C is superior to Device A!!!!

(Importance of Sn content control)

The stability of Device C is superior to Device A!!!!

(Importance of Sn content control)

ASn:Zn=30:50

CSn:Zn=40:40

Reference: APL, 95, 173508 (2009).

VDS=5.0V VDS=5.0V

0.4V 0.2V

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AssumptionSub-threshold current is due to the excitation of electron at DOS into conduction band and subsequent drift

EC

EV

EF

Ei

e`-

e-

e-

e-

MetalInsulator

Semiconductor

EA =EC -EF

)(1

FSSGS

F

GS

A

ENdVdE

dVdE

∝∝

FSSGSi ENVC ∆≈Q

Interpretation

Activation Energy Plot of ZIT TFTs

-4 -2 0 2 4 6 8 100.0

0.2

0.4

0.6

0.8

1.0

Device A Device C

Act

ivat

ion

ener

gy (e

V)

VGS (V)

Plot of activation energy and VGS

The much faster falling rate (∆EF/∆VGS ~ 1.2 eV/V) of EA in

device C compared to that (∆EF/∆VGS ~ 0.43 eV/V) of device A,

means that the Ntotal value is reduced by approximately 3

times compared to that of device G.

The much faster falling rate (∆EF/∆VGS ~ 1.2 eV/V) of EA in

device C compared to that (∆EF/∆VGS ~ 0.43 eV/V) of device A,

means that the Ntotal value is reduced by approximately 3

times compared to that of device G.

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ID C A B

Zn/(Zn+In+Sn ) 0.40 0.50 0.45

In/(Zn+In+Sn) 0.20 0.20 0.20

Sn/(Zn+In+Sn) 0.40 0.30 0.35

Nss,max (1017 cm-3eV-1) 1.9 3.2 2.7

Dit,max (1012 cm-2eV-1) 0.47 0.78 0.67

Stability Excellent Trap creationCharge trapping

Estimated Nss,max and Dit,max values for various cation composition

)log()(

eCDtNTqkSS

i

itchssB +=

where q is the electron charge, kB Boltzmann’s constant, T the absolute temperature, and tch the channel layer thickness.

To improve the temperature and gate-bias instability, it is of importance to reduced the overall trap density as possible as you can !!!To improve the temperature and gate-bias instability, it is of importance to reduced the overall trap density as possible as you can !!!

Reference: APL, 95, 173508 (2009).

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True Leader in Digital WorldSamsung SDIDesign Concept of New Oxide ChannelDesign Concept of New Oxide Channel

• Network former : Zn

• Mobility enhancer : In Sn (?)

• Carrier suppressor : Ga (bi pyramidal site) Zr,Al,Cu,Hf,Ti etc

• Network former : Zn

• Mobility enhancer : In Sn (?)

• Carrier suppressor : Ga (bi pyramidal site) Zr,Al,Cu,Hf,Ti etc

InGaZnO system: 1) IP issue, 2) Ga, In : high cost, rare element

Atomic structure CB minimum

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Mo SiO2

Si substrate

ZrInZnOIZOSiO2

Beyond IGZO?Beyond IGZO?

In2O3• Bix-byite structure

(C-type rare-earth crystal structure)• BCC (Ia3, number 206)• Lattice parameter 10.117A

Cu Kα (222): 30.61°C, (400) :35.49°C

In2O3• Bix-byite structure

(C-type rare-earth crystal structure)• BCC (Ia3, number 206)• Lattice parameter 10.117A

Cu Kα (222): 30.61°C, (400) :35.49°C

Novel ZrInZnO

• Cosputtering of ZrO2 and IZO target• Ga-free channel: Zr (carrier suppressor)• Zr0.4In1.2Zn0.4O3 composition

(In 60%, Zr 20%, Zn 20%)

• Cosputtering of ZrO2 and IZO target• Ga-free channel: Zr (carrier suppressor)• Zr0.4In1.2Zn0.4O3 composition

(In 60%, Zr 20%, Zn 20%)

In site

O site

Reference: Adv. Mat. 21, 329-333 (2009).

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25 30 35 40 45 50 55

As-deposited

150oC

250oC

350oC

Inte

nsity

(A.U

.)

2 Theta

Transition of tetragonal to cubic systemTransition of tetragonal to cubic system

(222)

(400)

• annealing temperature ↑

: lattice parameter ↓, a/c → 1


: grain size ↑


: FWHM ↓

• crystalline quality improved, as

annealing temperature ↑


: lattice parameter ↓, a/c → 1


: grain size ↑


: FWHM ↓

• crystalline quality improved, as

annealing temperature ↑

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(c) (d)

Microstructure Evolution of ZrInZnOMicrostructure Evolution of ZrInZnO

(e) (f)

As-deposited 350C annealed

EDS

• Average grain size : 8-9nm (as-dep)• Average grain size : 8-9nm (as-dep) • Average grain size : 12-13nm (350C)• Average grain size : 12-13nm (350C)


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-30 -20 -10 0 10 20 30 40

1x10-10

1x10-8

1x10-6

1x10-4

VDS = 0.1V

VDS = 5.1V

I DS (A

)

VGS (V)

Before stressAfter 60Hrs stress

TFT property of ZrInZnOTFT property of ZrInZnO

• Device properties: mobility 4cm2/Vs, Ion/off 1e7• Promising robust channel material • Device properties: mobility 4cm2/Vs, Ion/off 1e7• Promising robust channel material

Carrier control/output Stability data

150 200 250 300 350 400 4501012

1014

1016

1018

1020

0

1

2

3

4

5

n e (cm

-3)

Annealing Temperature (oC)

ne Hall mobility

Hal

l mob

ility

(cm

2 /Vs)

0 5 10 15 200.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

10V12V14V

16V

18V

VGS=20V

Dra

in C

urre

nt (A

)

Drain Voltage (V) 0 10 20 30 40 50 600.1

1

10

100

∆V th

(V)

Stress time (Hrs)

ZrInZnO at 250°CZrInZnO at 350°CInGaZnO at 350°C


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Soluble Oxide TFTsSoluble Oxide TFTs

Advantages

• No photolithography process• No vacuum deposition equipment• High productivity (Simple process)• Roll to roll process• Flexible display application• Suitable for large size display

• No photolithography process• No vacuum deposition equipment• High productivity (Simple process)• Roll to roll process• Flexible display application• Suitable for large size display

Issues

• High annealing temp: precursor (400-600C), nano-particle (200-300C)

• Extremely poor reliability

• High annealing temp: precursor (400-600C), nano-particle (200-300C)

• Extremely poor reliability

True Leader in Digital WorldSamsung SDIZIO TFTs: Oregon State Univ.ZIO TFTs: Oregon State Univ.

Device Fabrication• ZnCl2+InCl2 dissolving in CH3CN (acetonitrile)• Spin-coating or ink jet printing & 600C anneal• Mobility: 16cm2/Vs (spin-coating) , 7.4cm2/Vs (printing)

• ZnCl2+InCl2 dissolving in CH3CN (acetonitrile)• Spin-coating or ink jet printing & 600C anneal• Mobility: 16cm2/Vs (spin-coating) , 7.4cm2/Vs (printing)

Physical properties and Device performancePhysical properties and Device performance

Reference: D. H. Lee et al., Adv. Mater., 19, 843 (2007).

Formation mechanismFormation mechanism

True Leader in Digital WorldSamsung SDIZTO TFTs: Oregon State Univ.ZTO TFTs: Oregon State Univ.

Device Fabrication• ZnCl2+SnCl2 dissolving in CH3CN (acetonitrile)• Sincoating & 600C anneal• Mobility: 16cm2/Vs , Ion/off 1e6

• ZnCl2+SnCl2 dissolving in CH3CN (acetonitrile)• Sincoating & 600C anneal• Mobility: 16cm2/Vs , Ion/off 1e6

Surface & compositionSurface & composition Device structure & performanceDevice structure & performance

Reference: Y. J. Change et al., ESL, 10, H135 (2007).

True Leader in Digital WorldSamsung SDIIZO TFTs: KAISTIZO TFTs: KAIST

Device Fabrication• Zinc acetate+Indium acetate dissolving in methoxyethanol,

diethanolamine (stabilizer)• Sincoating & 500C anneal• Mobility: 7.3cm2/Vs , Ion/off 1e7

• Zinc acetate+Indium acetate dissolving in methoxyethanol, diethanolamine (stabilizer)

• Sincoating & 500C anneal• Mobility: 7.3cm2/Vs , Ion/off 1e7

Mass loss & microstructureMass loss & microstructure Device structure & performanceDevice structure & performance

Reference: C. G. Choi el al., ESL, 11, H7 (2008).

True Leader in Digital WorldSamsung SDIIGZO TFTs: Yonsei UnivIGZO TFTs: Yonsei Univ

Device Fabrication• Zinc acetate+Indium nitrate+Galium nitrate dissolving in

methoxyethanol, monoethanolamine (stabilizer)• Sincoating & 400C anneal• Mobility: 1.2cm2/Vs , Ion/off 4e6

• Zinc acetate+Indium nitrate+Galium nitrate dissolving in methoxyethanol, monoethanolamine (stabilizer)

• Sincoating & 400C anneal• Mobility: 1.2cm2/Vs , Ion/off 4e6

Mass loss & microstructureMass loss & microstructure Device structure & performanceDevice structure & performance

Reference: G. H. Kim et al., APL, 94, 233501 (2009).

True Leader in Digital WorldSamsung SDIZnO TFTs: Oregon State UnivZnO TFTs: Oregon State Univ

Device Fabrication• Zinc nitrate+ NaOH in DI water Hydrated precipitate Rigorous

purification• Sincoating or Inkject printing & (150-300C) anneal• Mobility: 4-6cm2/Vs (300C), 0.4cm2/Vs (150C)

• Zinc nitrate+ NaOH in DI water Hydrated precipitate Rigorous purification

• Sincoating or Inkject printing & (150-300C) anneal• Mobility: 4-6cm2/Vs (300C), 0.4cm2/Vs (150C)

Morphology & microstructureMorphology & microstructure Device structure & performanceDevice structure & performance

Reference: S. T. Meyers et al., J. Am. Chem. Soc., 130, 17603 (2008).

True Leader in Digital WorldSamsung SDISummary (1)Summary (1)

a-Oxide TFTs are the most promising technology as an active device

for large area AMOLED.

Strong points of a-Oxide TFT are scalability, uniformity and device

performance in terms of kink effect & hot carrier effect.

Reliability of a-Oxide TFT was improved by using proper materials and

optimization of the process

Oxide TFTs have potential to realize transparent AMOLED and

high performance color flexible AMOLED.

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zn 기반 산화물 트랜지스터 소자의 이해 및 연구 현황 -...

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