View
4
Download
0
Category
Preview:
Citation preview
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 1
Transparent Electronics for Active Matrix Displays
Thomas Riedl
Lehrstuhl für Elektronische Bauelemente, Bergische Universität Wuppertal
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 2
City: WuppertalState: North-Rhine-Westfalia
Pop.: 353.308
City of Wuppertal
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 3
Bergische Universität Wuppertal
since 1863 School of Engineering
1972 Foundation of BU Wuppertal
7 Faculties
14,000 Students
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 4
Electrical, Information and Media Engineering
1100 Students
21 Professors
Focus Areas:
→ Automotive Engineering
→ Print & Media Technology
→ Renewable Energy Systems
→ Polymer Electronics
Campus Freudenberg
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 5
Institute of Electronic Devices, University of Wuppertal, Germany (T. Riedl)
since : 01.10.2009
former: Advanced Semiconductors Group
Institute of High-Frequency Technology, TU Braunschweig
Institute of Electronic Devices
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 6
New Labs - Institute of Electronic Devices
400 m2
220 m2 lab space (clean-room)
Start-up: 2010
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 7
Institute of Electronic Devices, University of Wuppertal, Germany
Reliability Analysis
Transparent Oxide-Electronics
OrganicPhotovoltaics
Organic ElectronicsOLEDs
Functional Molecular Systems
Organic Lasers/Amplifiers
Research Topics
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 8
→ Transparent Electrodes (OLED, OPV)
→ Thin-Film Encapsulation
→ Oxide TFTs
Metaloxides as Components of AM-Displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 9
→ Transparent Electrodes (OLED, OPV)
→ Thin-Film Encapsulation
→ Oxide TFTs
Metaloxides as Components of AM-Displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 10
OLED Displays
→ no back-lighting
→ large viewing angle
→ low weight
→ flexible
→ cost effective technology
→ low energy consumption
LG 15 inch OLED TV (15EL9500)
Samsung S8300 UltraTOUCH
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 11
OLED Lighting
OLEDs: next-generation lighting technology
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 12
Transparent Displays
Minority ReportTM and © 2002 Twentieth Century Fox and Dreamworks, LLC. Transparent OLED AVATAR TM and © 2009 Twentieth Century Fox
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 13
Transparent Organic Light Emitting Layers
taylored organic layers: + absorption in the UV (< 400 nm) + emission in the visible
→ large „Stokes shift“
300 350 400 450 500 550 600 650 700
5.0x104
1.0x105
1.5x105
0.0
0.2
0.4
0.6
0.8
1.0 Absorption Emission
abso
rptio
n co
effic
ient
, cm
-1
wavelength, nm
PL in
tens
ity, a
.u.
guest-host systems
TCTA
Ir(ppy)3
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 14
Hardware
Metall-Cathode
Organic Semiconductor
Transparent Anode e.g. ITO
Glass-Substrate Light extraction
⇒ entirely transparent OLEDs
Transparent Cathode (TCO) Light extrcation
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 15
Transparent Conducting Oxides on Top of Organics
Organic semiconductors are brittle !
→ low processing temperatures (< 80 °C)
→ avoid oxygen + high-energy particles/radiation
Bonding energies:C-C (3.73 eV), C=C (6.21 eV)
Typical by-products : charge carrier trapsnon-radiative defectsbut:
→ transparent oxides contain oxygen→ sputtering, pulsed laser deposition→ particle energies ∼1-100 eV ?→ UV radiation
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 16
Transparent OLED Structure
Adv. Mater. 20, 3839 (2008)
→ bullet-proof vest (WO3, MoO3, …)
→ thermal deposition of WO3, MoO3, …
→ WO3, MoO3 transparent, conductive
→ record-efficiency: 30 lm/W, 38 cd/A
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 17
WO3 as Sputter Protection Layer - SIMS Analysis
Analysis of particle penetration → secondary ion mass scectroscopy
Sputter particles penetrate WO3 layer only by 40 nm → protection for OLED
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 18
MoO3 High-Work-Function Material
Appl. Phys. Lett. 95, 123301 (2009)
→ transition metal oxides: n-type semiconductors
→ no electron blockers
→ high workfunction, very deep valence band
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 19
Transparent OLEDs
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 20
Semi-transparent Organic Cells
Transparent electrodes → semi-transparent OPV
currently ∼ 2.5 % efficiency
lightAppl. Phys. Lett. 94, 243302 (2009)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 21
Vision
Terminal 2G Airport Paris Charles de Gaulle
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 22
Indium-Tin-Oxide (ITO) as TCO
+-
→ Indium is scarce and expensive
→ resources last for only 20 years(US geological survey 2006)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 23
Issues with Indium-Tin-Oxide (ITO)
→ identify alternatives
ITO consumption in 2006 and 2030
Quelle: Fraunhofer Gesellschaft 2009: „ Rohstoffe für Zukunftstechnologien“
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 24
Al doped ZnO
ZnO is cheap and abundant !
• ZnO:Al2O3 (4 wt%)
• pulsed laser deposition (PLD)
• sputter deposition
„our“ AZO:
→ optimum conductivity: 4000 S/cm (n=6x1020 cm-3; µn=42 cm2/Vs)
c.f. ITO (MERCK) 4700 S/cm
→ high transmissivity in the visible:
@ 550 nm: α=200 cm-1 → T= 98 % (1µm film)→ Rsheet = 4 Ω/sq. Appl. Phys. Lett. 91, 041113 (2007)
Appl. Phys. Lett. 93, 073308 (2008).
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 25
ZTO/Ag/ZTO
Zinc-Tin-Oxide (ZTO)
→ high carrier mobility
→ highly transparent > 80 %
→ simple processing technology
sputter-deposition at room temperature
ZTO (30 nm)Ag
ZTO (30 nm)
400 500 600 700 8000
20
40
60
80
100
6nm Ag
trans
miss
ivity
(%)
wavelength (nm)
ZTO/Ag/ZTO
70nm ITO (pure)
100
101
102
103
104
105
0 2 4 6100
101
102
103
104
cond
uctiv
ity (S
/cm
)
Ag thickness
shee
t res
istan
ce (Ω
/sq)
RT ITO
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 26
ZTO/Ag/ZTO
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 27
Alternative Transparent Electrodes
Metall Oxide
Metall Oxide
charge transfer
Charge transfer → doping of the oxide
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 28
Alternative Transparent Electrodes
TPBi
TPBi:Ir(ppy)3
ZTO 42 nm
ITO
BPhen:Cs2CO3
Ag 10 nm
ZTO 42 nm
MoO3
TCTA
0 1000 2000 30000
10
20
30
40
50
10
20
30
40
50
curre
nt e
fficie
ncy
(cd/
A)
luminance (cd/m²)
powe
r effi
cienc
y (lm
/W)
ηphot = 43 cd/A, ηlum = 30 lm/W @ 1000 cd/m²
Kooperation T. Winkler, TU-BS
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 29
Alternative Transparent Electrodes
>80 % transmission @ 500 nmdefect free!
Kooperation T. Winkler, TU-BS
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 30
→ Transparent Electrodes (OLED, OPV)
→ Thin-Film Encapsulation
→ Oxide TFTs
Metaloxides as Components of AM-Displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 31
Thin-film Encapsulation for OLEDs
substrate
insulationorg. thin filmsmetal
ITO
Glass lid
Conventional glass-lid encapsulation:
→ not flexible, heavy
→ expensive
→ problematic for transparent OLEDs
⇒ efficient thin-film encapsulation needed
„food packaging“
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 32
Temperature aspects
HTL ETL
Tg = 95 °CTg = 170 °C
→ organic materials form glassy films: typically Tg = 50 - 200°C
→ Low-temperature (T < 100 °C) encapsulation process required
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 33
ALD: Technique for extremely dense and conformal dielectric layers
highly reactive precursorse.g. for Al2O3 Trimethylaluminum (TMA) and H2O
→ low processing temperatures (< 100°C)
→ promising for barrier layers for organic devices
Atomic Layer Deposition
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 35
Calcium as Sensor
Array of Ca Pads
Without encap → 100 nm Calcium completely oxidized (90 s in air)
expected: with encap. (WVTR=1x10-6 g/m2 d) → 700 days
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 36
Corrosion of Al2O3
100 nm Al2O3
Large area encapsulation (80 °C, 80 % RH)
fresh 48 h 118 h
95 nm Al2O3 + 5nm ZrO2
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 37
Nano-laminates as Encapsulation Layers
SubstrateOLED
cyclic deposition of Al2O3 and ZrO2
20 cycles Al2O3 (2 nm)20 cycles ZrO2 (3.8 nm)
aim:
→ protection against corrosion
→ forced amorphicity (neat ZrO2 polycrystalline)
→ avoid permeation channels
next generation thin film encapsulation → nano-laminates
Adv. Mater. 21, 1845 (2009).Tetrakis(dimethylamido)zirconium(IV)
Precursor for ZrO2 preparation
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 38
20 h 60 h 160 h
100 nm Al2O3 + ZrO2 nanolaminate
Statistical Defects
Adv. Mater. 21, 1845 (2009).
Large area encapsulation (70 °C, 70 % RH)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 39
encapsulation permeation rate forwater
(g/m² day)
permeation rate foroxygen
(cm³/m² day)Al2O3 130 nm @ 80 °C 8.8 x 10⁻⁵ 3.9 x 10⁻²
Al2O3 & ZrO2 130 nm @ 80 °C 4.7 x 10⁻⁵ 2.1 x 10⁻²
Test conditions (climate cabinet): 70 °C and 70 % RH
Permeation Rates
Adv. Mater. 21, 1845 (2009).
with Ea = 92 kJ/mol → 5 x10-7 (at RT)
→ Low permeation rates maintained down to 40 nm thin laminates !
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 40
OLED Lifetime
w/o encap: 350 h
Al2O3: 8,700 h
ZrO2/Al2O3 NL: 22,000 h
glass lid + getter: 56,000 h
Substantially improved OLED lifetime through ALD nanolaminate
→ close to benchmark of glass lid encap
Starting luminance 1,000 cd/m2, constant-current mode
Appl. Phys. Lett. 94, 233305 (2009).
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 41
Underwater OLEDs
ALD barriers allow for wet chemical post-processing:
→ photo-lithography→ printing
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 42
→ Transparent Electrodes (OLED, OPV)
→ Thin-Film Encapsulation
→ Oxide TFTs
Metaloxides as Components of AM-Displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 43
Transparent Displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 44
Transparent AMOLED Displays
Ice Touch YP-H1 - Samsung CES 2010
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 45
Passive-Matrix OLED (PMOLED) Displays
⇒ pixel brightness >> display brightness
e.g. VGA-Display (640 x 480 pixels) 100 cd/m2
→ required pixel brightness > 48,000 cd/m2
→ reduced efficiency, reduced lifetime
Passive-Matrix Display:
→ row by row addressing
→ ok for small area/low resolutionanode
cathode
solution: active-matrix addressing
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 46
Active-Matrix Addressing
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 47
BMBF Project:
Grundlagenuntersuchungen zu Transparenten Elektronischen Bauelementen
und Schaltungen
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 48
Transparent Semiconductors
ZnO-SnO2 : abundant, non-toxic
wide band gap (> 3eV) → see-through
deposition by sputtering or PLDMinami, MRS BULLETIN/AUGUST 2000
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 49
Transparent TFTs on Glass
channel: (ZnO)x (SnO2)1-x (ZTO)
Drain-Source Electrodes: ZnO:Al (AZO)
Gate dielectric: Al2O3 (by atomic layer deposition)
• TEM: ZTO amorphous structure • Transmissivity > 80 %
Bottom-Gate stucture
ZTO
epoxy
gate dielectric
ITO
glass
TEM cross section
TEM images:Dr. Thomas WeimannPeter Hinze
Appl. Phys. Lett. 90, 063502 (2007)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 50
Plasma assisted deposition
-40 -30 -20 -10 0 1010-10
10-9
10-8
10-7
10-6
10-5
10-4
atomarer O
I DS (
A)
UGS (V)
molekularer O
-40 -30 -20 -10 0 10
0.000
0.002
0.004
0.006
0.008
0.010
atomarer Omolekularer O
I ds0.
5 (A0.
5 )Ugs (V)
→ severe hysteresis → defect states
→ elevated off current
→ Threshold shifted towards negative Ugs → elevated carrier density
µsat = 6 cm2/Vs
µsat = 10 cm2/Vs
Oxygen partial pressure: 2x10-4 mbar (PLD)
UthrUthr
Appl. Phys. Lett. (in preparation)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 51
400 500 600 nm 800
0
20
40
60
%
100
(ZnO)x(SnO2)1-x , d=1µm atomar O, molecular O,
Tran
smiss
ion
λ
Optical Properties
• many sub-bandgap states
• shallow donors
→ ZTO carrier density (Hall):
Molekular O : n = 1019 cm-3
Radical O : n = 2×1016 cm-3
radical O molecular O
ZTO-layer thickness: 1 µm
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 52
ESCA Analysis
ZTO Layer
photoelectronsX-rays
SiO2 Substrate
O1sZn2p3/2Sn3d5/5
SiO
2
SiO
2
ZTOZTO
Gradient in [Zn]-content → out-diffusion of Zni → defects: excess zinc (Zni)
0 10 20 30
44
45
46
47
48
49
50
51
O c
onc.
(at
%)
x (nm)
atomar Oxygen molecular Oxygen
-5 0 5 10 15 20 25 30
0.92
0.94
0.96
0.98
1.00
1.02
[Zn]
/([Zn
]+[S
n]) (
norm
.)
x (nm)
atomar O molecular O
Sputtering (Ar-Ions)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 53
TTFT transfer-characteristics
Ion/Ioff=106
µFE,SAT = 13 cm2/Vs
(c.f. a-Si: µFE,SAT = 1 cm2/Vs)
Uth = -1..1 V
→ no hysteresis measureable→ low sensitivity towards visible light
TTFT output-characteristics
ZTO-TTFTs on Glass
0 1 2 3 4 5 6
01020304050607080
Ug = -3...5 V
I D (µA
)
Uds (V)
-6 -4 -2 0 2 4 61E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
-2.0x10-3
0.0
2.0x10-3
4.0x10-3
6.0x10-3
8.0x10-3S = 0.45 V/decade
µfe = 13 cm2/Vs
I D (A
)
UG (V)
Vth
I D1/2 (
A1/2 )
phys. stat. sol. (rrl) 1, 175 (2007)
Appl. Phys. Lett. 90, 063502 (2007)Appl. Phys. Lett. 91, 193504 (2007)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 55
TTFTs and Transparent OLEDs
P. Görrn et al., Adv. Mater. 18, 738 (2006) building block of transparent AMOLED displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 56
ZTO Pixeldriver
C = 12.3 pF
W/L = 100 µm/10 µm
pixel area: 180 × 240 µm2
transmissivity 80 %Solid State Electron. 53, 329 (2009). IEEE/OSA J. Displ. Technol. 5, 810 (2009)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 57
ZTO Pixeldriver
Requirement:
full HD (1,920x1,080 pixels) + 100 Hz refresh
frame-time 10 ms
max. pixel charging time ∼10 µs
Solid State Electron. 53, 329 (2009). IEEE/OSA J. Displ. Technol. 5, 810 (2009)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 58
smart pixel active pixel
stability considerations for analog driving TFT:
drift in the TFT device parameters ⇒ drift in pixel brightness
Transparent Active Pixel
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 59
a-Si TFT Instability – Ghost Images
Original image (stress for TFTs) homogeneous background withGhost image
Lee
et a
l. IE
EE
Ele
ctro
n D
evic
e Le
tt. 2
7, 8
30(2
006)
AMOLED Display with Si TFT backplane
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 60
TFT Stability
Shift of the threshold voltage after 10 h gate bias stress Ug=10 V
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 61
TFT Stability
Depending on the composition, the threshold is ….
• …. increased by trapping of electrons in the dielectric• …. lowered by deep state creation in the ZTO
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 62
30 35 40 45 50 55 60 65 70-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
250°C 350°C 450°C
∆V th
/V
Zn:Sn ratio (%)100 1000 10000 100000
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
stress time/s ∆
V th/V
Zn concentration (%)65
333836
46
45
Appl. Phys. Lett. 90, 063502 (2007)
[Zn]:[Sn] compositions for extremely high TFT stability
Shift of the threshold voltage after 10 h gate bias stress Ug=10 V
Our devices with varied [Zn]:[Sn] ratio
Compositional Dependence
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 63
1,000 h Lifetime Test
after 1,000 h: ∆Vth = 320 mV for DC current stress 100 × IOLED
• c.f. a-Si TFT ∆Vth = 2 V after 5 h (A. Nathan et al. J.Vac. Sci. Technol. 24 , 875 (2006))
• IGZO TFT ∆Vth = 1.6 V after 10 h stress (SAMSUNG SID 2008)
⇒ ZTO unsurpassed stability for TFTs with amorphous semiconductorphys. stat. sol. (rrl) 1, 175 (2007) Appl. Phys. Lett. 90, 063502 (2007)
-6 -4 -2 0 2 4 6 8 10 1210-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
I ds/A
UG/V
before stress after 1000h
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 64
Ambient Temperature
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 65
Impact of Illumination – IGZO Case
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 66
Impact of Illumination – IGZO Case
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 67
Illumination – Issues with Zinc Indium Oxide
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 68
Illumination – Zinc Tin Oxide
Strong influence of:
→ wavelength
→ annealing temperature
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 69
Illumination– Zinc Tin Oxide
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 70
Interaction with Oxygen - IGZO
problematic for encapsulationas required in OLED displays
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 71
Encapsulation of Oxide TFTs – Zinc Tin Oxide
P. Görrn, T. Riedl et al. J. Phys. Chem. C 113, 11126 (2009).
→ Higher binding energy of O2 in ZTO-
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 72
Encapsulation of Oxide TFTs – Zinc Tin Oxide
J. Phys. Chem. C, 2009, 113 (25), pp 11126–11130
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 73
Encapsulation of Oxide TFTs – Zinc Tin Oxide
→ change of threshold voltage ∆Vth < 1V
J. Phys. Chem. C, 2009, 113 (25), pp 11126–11130
novel encapsulation strategy:
→ deposit thin (1nm) encap. first
→ re-expose to oxygen
→ oxygen can re-adsorb at channel
→ apply full encapsulation
→ pre-encap. clamps adsorbed Oxygen
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 74
Future Prospects
→ target 3-D Displays
→ resolution > full HD
→ 480 Hz refresh
→ beyond reach for a-Si electronics
→ metal-oxide TFTs key technology
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 75
Printed Oxide TFTs
harvest benefits of both worlds:
→ stability/performance of in-organic oxide semiconductors
→ large-area, high-throughput, low-cost printing techniques(formerly domain of polymer electronics)
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 76
Printed Oxide TFTs
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 77
Printed Oxide TFTs
In2O3 (In chloride) 400 °C
Zn-In-O (Zn chloride, In choride) 600 °C
Zn-Sn-O (Zn acetate ,Tin acetate) 500 °C
Ga-In-O (Ga(NO3)3) 600 °C
Ga-In-Zn-O (ZnAc, Ga(NO3)3, In(NO3)3) 300 °C
In-Sn-O (In chloride, Tin chloride) 250°C
........
Literature reports for liquid processing of metal oxides
Metal-oxide system Precursors used Annealing temp
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 78
Printed In-Zn-O TFTs
Precursors:
Indium nitrateZinc acetate
Process-temp.: 450 °C
µFE,SAT > 6 cm2/Vs
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 79
Printed Oxide TFTs
stability vs. stress ?
hysteresis ?
Recent data 5 cm2/Vs
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 80
Printed Oxide TFTs
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 81
Printed Oxide TFTs
ZnNO3,Ga(NO3)3, In(NO3)3 aqueous solution
Metaloxide formation at 95°C
Mobility: 2.3 cm2/Vs
Y.-H. Yang et al.
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 82
Summary
Transparent ZnO-SnO2 TFTs 80 % transmissivity, outstanding stability
Transparent OLED technology> 40 cd/A , 80 % transmissivity
ALD Thin film encapsulationWVTR 5×10-7 g/(m2day), lifetime > 20 000 h
Transparent drivers electronics100 Hz, full HD, >4,000 cd/m2
Thomas Riedl
Institute of Electronic DevicesFAHL 2010, Leipzig, 28.09.2010
Transparent Electronics for Active Matrix Displays– Slide 83
Acknowledgement
Co-workers at :
TU Braunschweig
PTB
Princeton University
Innovation Lab Heidelberg
Funding:
Recommended