Hosono, Hideo

English

Lehigh University: Lehigh Preserve

Lehigh University
Lehigh Preserve
International Workshop on Scientific Challenges for
Glass Research Glass Conferences and Workshops
Spring 4-15-2007
Transparent amorphous oxide semiconductors and
their TTFT applications
Hideo Hosono
Tokyo Institute of Technology, Japan
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scientificchallenges
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Recommended Citation
Hosono, Hideo, "Transparent amorphous oxide semiconductors and their TTFT applications" (2007). International Workshop on
Scientific Challenges for Glass Research. 2.
https://preserve.lehigh.edu/imi-tll-conferences-scientificchallenges/2
Hideo HOSONO
Frontier Collaborative Research Center 
& Materials and Structures Laboratory,  
Tokyo Institute of Technology, Yokohama, JAPAN
&  ERATO-SORST, Japan Science and Technology Agency (JST)
Transparent Amorphous Oxide 
Semiconductors and Their TTFT 
Application
Thin Film Transistor
flexible electronics, 
Electronics everywhere
http://www.pioneer.co.jp/
present : TFT on glass future : TFT on plastic
: Switching device in display
Semiconductor:a-Si:H ?
Giant-microelectronics
TFT: Active Matrix Display
TFT
pixel
光
Market Forecast of Flexible Display
Sources：iSuppli
Examples of Flexible TFT
Organic TFT
Philips & Polymer Vision
Plastic Logic
Low mobility
Poor stability
Low process temperature
Long-term stability
High mobility
Novel Material
Heavy 
Expensive (Passivation)
a-Si on SUS foil
LG. Philips LCD
poly-Si 
(Transfer Technique)
SEIKO EPSON
Difficulty in large area fabrication
Expensive
LG Philips
Plastic Logic
SEIKO EPSON
Why amorphous semiconductor
semiconductor amorphous
Excellent controllability
of carrier
low T formation of 
large area thin films
Amorphous semiconductor
Wide controllability of carrier concentration.
High optical transparency in invisible region.
Room temperature and large area deposition.
Unique carrier transport properties
Adv. Mater. 15,1409 (2003)
AOSs based flexible pn diodes
A rectifying ratio : >103
Vth : ~2V
-4 -2 0 2 4
-2
0
2
4
6
8
10
 
 
C
u
r
r
e
n
t
 
d
e
n
s
i
t
y
,
 
J
 
(
 
A
 
c
m
-
2
 
)
Voltage ( V )
History of amorphous semiconductor
1950. 1960. 1970. 1980. 1990. 2000
Photoconductivity in a-Se(Xerography)
Glassy semicond.(V2O5 based oxide)
Chalcogenide glass   DVD)
Switching and memory effect in a-chal. film
a-Si:H ‘Giant-Microelectronics’
Flexible electronics
( novel a-sc)
Proposal of materials design concept 
for a-TAOS with large mobility
Proc. of ICAMS-16
Ionic Amorphous Oxide Semiconductor : 
novel class of a-Semicon.
CovalentIonic
Wide Gap
Narrow Gap
a-metal
a-Si:H
a-Chal.
Glassy oxide
Semicon.
Conventional
glass
Molten salt
Ionic amorphous
oxide semicon.
JNCS(1996)
Material design concept (electron pathway)
crystal
amorphous
ionic oxide semicon. 
M:(n-1)d10ns0 (n≥4)
covalent semicon.
Ionic amorphous oxide semiconductors (N-type)
Advantages
(found in1995-2001)
Optical 
transparency
in visible region
Electrical 
conductivity 
Amorphous
e.g. a-2CdO･GeO2, a-CdO･PbOx, a-AgSbO3, a-InGaO3(ZnO)m
Transparent amorphous oxide semiconductors
a-In2O3:Sn
・Low temperature deposition        flexible electronic device  
・No long range ordering        reduction of severe requirements for PN-junction
・Large electron mobility compared to the conventional a-semiconductors.
Conductivity change upon H+- implantation
4 6 40 80
-10
-5
0
before implantation
Ea= 1
 eV
2 ? 1014 cm-2
Ea= 0.06
 eV
2 ? 1015 cm-2
E
a
 < 1 m eV
2 ? 1016 cm-2
1000 / T  ( K-1 )
T ( K )
L
o
g
 
σ
 
 
(
 
S
 
c
m
-
1
 
)
300 200 120 60 13
 
H+:40kV+70kV
1000 20000
50
100
after implantation
T
R
A
N
S
M
I
T
T
A
N
C
E
 
 
(
 
%
 
)
WAVELENGTH ( nm )
before implantation
Sample: sputtered thin film(300nmt)
AAPL(1995)
EF is continuously controllable from
~Eg/2 to above mobility gap
Mobility  amorphous 15 cm2(Vs)-1  cf. crystal 20cm2(Vs)-1
EF cannot exceed mobility gap
a-Si:H doping  limit
EF never enters conduction band extended 
states by doping
P30 + Si40 → P4+ + Si3-
Doping creates D- state
Why doping is inefficient for a-Si:H ?
P Si P+ Si
-
Carriers are NOT generated
Mott-Street model
-10 0 10
Ge 4pCd 5p
Cd 4d
O 2p
Ge 4s
Conduction BandValence Band
Total
Cd 5s
 
 
 
10 0 -10
MO Energy (eV)
D
O
S
 
(
a
r
b
.
 
u
n
i
t
s
)
 
PES
IPES
 
I
n
t
e
n
s
i
t
y
 
(
a
r
b
.
 
u
n
i
t
s
)
EF
 
Binding Energy (eV)
Observed and calculated DOS
Valence Band Conduction Band
Phys.Rev.B(2002)
(b) amorphous(a) crystalline
Ge
Ge
Cd CdCd
 
 
 
Cd
Cd
Cd
Contour map of wave function @  conduction band bottom
Cd-Cd correlations in RMC-fitted model
3D-percolated!
crystalline
Cd 5s
d(Cd2+-Cd2+)< 2r(Cd 5s)
PRB(2002)
Electron Transport in a-IGZO
APL(2004)
m*=0.35
EF
Ec
Eth
EF
µHall ~ 1 cm2(Vs)-1µHall >10
Eth  >  EFt <
Ne <  101８ cm-3e > 8 -3
APL(2004),TSF(2005).
Carrier Concentration and conduction
electron
Ionic Amorphous Oxide Semicon.
In-Ga-Zn 
-O
10~60
norm
al
Band 
condu-
ctionIonic
V2O5
-P2O5~10-4
hoppingcovalent 
+
Ionic
Oxides
(glass 
semiconductors）
(Ionic 
amorphous oxide 
semicondutors)
Tl2Se-
As2Se3
< 10-3 abnor
mal
hoppingcovalentChalcogenide
Si:H~1abnor
mal
hoppingcovalentTetrahedral
ExampleMobility
(cm2/(Vs))
Hall
effect
Mecha
-nism
Chemical 
bond
Material 
system
W / L : 200 / 50 (µm)
Transparent FET on plastic
Device structure
200µm
(no passivation)
Amorphous InGaZnO4 Thin Fims
Stable up to ~500 ºC
RT
400 ºC
500
600
700
t=200nm thick
Pulsed Laser deposition @ RT
µsat = 12 cm2(Vs)-1 ON/OFF ratio =106
W / L : 200 / 10 (µm)
Transistor Performance
output transfer
Nature(2004)
High performance transparent FET was 
fabricated on PET substrate
N-type AOS, In-Ga-Zn-O (a-IGZO)
Localized to extended state
Y2Ox (high k) as gate insulator &  RT
>10 cm2(Vs)-1 @Ne >1018 cm-3
High mobility & carrier controllability
Material exploration
Carrier transport
Device fabrication
µHall >15 cm2(Vs)-1  :Ne <1015 -1021 cm-3
ON / OFF ratio ~106
Normally-Off (Vth ~+1 V) 
µsat ~ 12 cm2 (Vs)-1
cf. ~1 for a-Si:H, pentacene
S = ~0.2 V/dec
a-IGZO can be deposited on plastic by the same process as ITO
Large process merit 
c
f
Current Status of TFT for  Elexible Displays
0.2 
~8
~12 
RT 
スパッター
アモルファ
ス-IGZOa-Si:H
1.30.40.2
~5>65~6(log10)
~50.50.5
300300<100
PLDCVD sputter
a-IGZOPoly-ZnOPentaceneChannel material
S (V/decade)
Current ON/OFF
Vacuum Evap.Thin Film Fabrication
Max. Tem.(℃)
Mobility(cm2V-1s-1)
Spec for Large-sized OLED TV Panel
@E - MRS2006
cm2/Vs1-10µFE
V for 105 hrs< 1ΔVTH
0.23.05.0ΔVTH (V)
IGZOIZOZnO
W/L=200/4 µm, 3 µA
Active Layer
/Pixel x 300hrs
SID2006
Long Term Stability
Long Team Stabilty Test(SAIT)
5-stage RO
0.5 mm
VDD
VGG
=
Ld-TFT
Dr-TFT
Ti/Au/Tisputter
IGZO
SiO2
Au/Ti
glass
Ti/Au/Ti
Au/Ti
glass
etchinginsulator
etchingsemiconductor
lift-offmetals
patterning
L Ld = L Dr = 10 µm
β R = (W / L) Dr / (W / L) Ld = 5
410 kHz (0.24 µs/stage), 7.5 Vp-p
@ Vdd = +18 (V)
14
12
10
8
6
4
2
0
V
o
l
t
a
g
e
 
(
V
)
Time (2 µs / div.)
Vdd = +18 V
0.1
1
10
100
D
e
l
a
y
 
p
e
r
 
s
t
a
g
e
 
(
µ
s
)
20151050
V dd (V)
10
8
6
4
2
0
V
oltage sw
ing (V
p-p )
amorphous/oxide TFT-based 
Ring Oscillators
?+80-80+30VDD (V)
P3HT a-IGZOIGO
?
?
?
9.510683fOSC (kHz)
APL 81, 
1735 
(2002)
0.68
2 – 5
Organic
605L (µm)
SSE 50, 
500 
(2006)
EDL 5, 
224 
(1984)
Ref.
110.54Δt(µs/stage)
Oxide
a-Si:H


OLED
monolithic
2Tr-1C
pixel driver
Gate insulator;
Si3N4
3.5’ OLED using TAOS-FET Backplane
LG (IDW ‘06)
Images of Flexible Electrophoretic Displays Driven with a-
IGZO TFT Array
Electrophoretic imaging film supplied by 
Thickness : 320 µm
Weight     : 1.3 g
Toward New Continent of 
Transparent Oxide Electronics
?
Flexible displays


Transparent amorphous oxide semiconductors and their TTFT applications

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Transparent amorphous oxide semiconductors and their TTFT applications

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