Transparent Amorphous Oxide Semiconductors and Their TTFT Application Hideo HOSONO
Transparent Amorphous Oxide Semiconductors and Their TTFT Application
Hideo HOSONO Frontier Collaborative Research Center & Materials and Structures ...
Transparent Amorphous Oxide Semiconductors and Their TTFT Application
Hideo HOSONO Frontier Collaborative Research Center & Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, JAPAN & ERATO-SORST, Japan Science and Technology Agency (JST)
Thin Film Transistor : Switching device in display present : TFT on glass Semiconductor:a-Si:H
future : TFT on plastic ?
http://www.pioneer.co.jp/ Electronics everywhere
Giant-microelectronics
flexible electronics,
TFT: Active Matrix Display
TFT
光
pixel
Market Forecast of Flexible Display
Sources：iSuppli
Examples of Flexible TFT poly-Si (Transfer Technique)
a-Si on SUS foil LG. Philips LCD
SEIKO EPSON
Difficulty in large area fabrication Expensive
Heavy Expensive (Passivation) LG Philips
Organic TFT
SEIKO EPSON
Philips & Polymer Vision Plastic Logic
Novel Material
Low mobility Poor stability
Low process temperature Long-term stability High mobility
Plastic Logic
Why amorphous semiconductor
semiconductor Excellent controllability of carrier
amorphous 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
AOSs based flexible pn diodes
Current density, J ( A cm-2 )
10
8
6
4
2
0
-2 -4
-2
0
2
4
Voltage ( V )
A rectifying ratio : >103 Adv. Mater. 15,1409 (2003)
Vth : ~2V
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. Wide Gap Molten salt Ionic amorphous oxide semicon.
Conventional glass Glassy oxide Semicon. a-Chal.
Ionic
Covalent a-Si:H
a-metal Narrow Gap
Material design concept (electron pathway) covalent semicon.
ionic oxide semicon. M:(n-1)d10ns0 (n≥4)
crystal
amorphous
JNCS(1996)
Ionic amorphous oxide semiconductors (N-type) Optical transparency in visible region
Advantages ・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 H+:40kV+70kV
Sample: sputtered thin film(300nmt)
T(K)
0
200
×2
15
-2
10 cm Ea= 0.06 eV
120
×2
60
16
13
-2
10 cm Ea < 1 m eV
-5
×2
100
14
10 cm Ea= 1 eV
-2
before implantation
-10
4
6 40 -1 1000 / T ( K )
EF is continuously controllable from ~Eg/2 to above mobility gap
A
APL(1995)
TRANSMITTANCE ( % )
-1
Log σ ( S cm )
300
80
Mobility amorphous 15 cm2(Vs)-1
50
before implantation after implantation
0
1000
2000
WAVELENGTH ( nm ) cf. crystal 20cm2(Vs)-1
a-Si:H
doping limit
EF cannot exceed mobility gap
Why doping is inefficient for a-Si:H ?
EF never enters conduction band extended states by doping P30 + Si40 → P4+ + Si3Doping creates D- state
P
Mott-Street model
Si
P
+
Si
Carriers are NOT generated
-
Observed and calculated DOS
Intensity (arb. units)
IPES PES
EF
10
0
-10
Binding Energy (eV)
DOS (arb. units)
Valence Band Valence Band
Conduction Band Conduction Band
Cd 4d
Total Cd 5s O 2p
Ge 4s
-10
0 MO Energy (eV)
Cd 5p Ge 4p
10
Phys.Rev.B(2002)
Contour map of wave function @ conduction band bottom
Cd
Ge
Cd
Cd
Cd
Cd
Cd
Ge
(a) crystalline
(b) amorphous
Cd-Cd correlations in RMC-fitted model d(Cd2+-Cd2+)< 2r(Cd 5s) 3D-percolated!
Cd 5s crystalline
PRB(2002)
Electron Transport in a-IGZO
m*=0.35
APL(2004)
Carrier Concentration and conduction 1８ cm-3 N Nee 1018 cm -3
High performance transparent FET was fabricated on PET substrate Material exploration High mobility & carrier controllability N-type AOS, In-Ga-Zn-O (a-IGZO) µHall >15 cm2(Vs)-1 :Ne 10 cm2(Vs)-1 @Ne >1018 cm-3
µsat ~ 12 cm2 (Vs)-1
cf. ~1 for a-Si:H, pentacene
c fON / OFF ratio ~106
Normally-Off (Vth ~+1 V)
Device fabrication Y2Ox (high k) as gate insulator & RT
S = ~0.2 V/dec
a-IGZO can be deposited on plastic by the same process as ITO Large process merit
Current Status of TFT for Elexible Displays
アモルファ -IGZO スa-IGZO
Channel material
Pentacene
Thin Film Fabrication
Vacuum Evap.
CVD
PLD
スパッター sputter
Max. Tem.(℃)
6
~5
S (V/decade)
0.2
0.4
1.3
~8 0.2
a-Si:H Poly-ZnO
Long Term Stability Spec for Large-sized OLED TV Panel SID2006
µFE ΔVTH
1-10 cm2/Vs < 1 V for 105 hrs
Long Team Stabilty Test(SAIT) @E - MRS2006 W/L=200/4 µm, 3 µA µ /Pixel x 300hrs Active Layer
ZnO
IZO
IGZO
ΔVTH (V)
5.0
3.0
0.2
5-stage RO VDD VGG =
0.5 mm
Au/Ti
Au/Ti
IGZO
sputter Ti/Au/Ti
glass
SiO2
Ti/Au/Ti
glass
patterning metals
lift-off
semiconductor etching insulator
Ld-TFT
etching
L Ld = L Dr = 10 µm β R = (W / L) Dr / (W / L) Ld = 5
Dr-TFT
14
10 8 6 4 2 0
Delay per stage (µs)
Voltage (V)
Vdd = +18 V
10 8
10
6 4
1
2 0.1
0 0
Time (2 µs / div.)
5
10 15 V dd (V)
20
410 kHz (0.24 µs/stage), 7.5 Vp-p @ Vdd = +18 (V)
Voltage swing (Vp-p)
12
100
amorphous/oxide TFT-based Ring Oscillators a-Si:H
Oxide
Organic P3HT
IGO
a-IGZO
L (µm)
5
2–5
60
?
VDD (V)
+30
-80
+80
?
83
106
9.5
?
0.54
0.68
11
?
EDL 5, 224 (1984)
APL 81, 1735 (2002)
SSE 50, 500 (2006)
fOSC (kHz) Δt(µs/stag e) Ref.
OLED monolithic 2Tr-1C pixel driver
3.5
OLED using TAOS-FET
Backplane
Gate insulator; Si3N4
LG (IDW 06)
Images of Flexible Electrophoretic Displays Driven with aIGZO TFT Array
Thickness : 320 µm Weight : 1.3 g Electrophoretic imaging film supplied by
Toward New Continent of Transparent Oxide Electronics
