カーボンナノチューブfetの現状と将来展望 水谷孝...
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1Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
カーボンナノチューブFETの現状と将来展望
水谷 孝
名古屋大学工学研究科
Source Drain
CNT10 μm
Source
Top-gate
Drain
2Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
1. Introduction2. Work function dependence of the CNTFETs3. Contact resistance/chemical doping4. Preferential growth of semiconducting CNTs5. Surface potential measurement by electrostatic
force detection6. New applications7. Issues and prospects
Outline
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Carbon nanotubes
graphene
・small diameter: 1~2 nm・length: μm – mm (large aspect ratio)・built-in 1D structure・ n-m= 3k:metal
n-m= 3k: semiconductor: Eg(eV)=0.9/d(nm)・high current density・large surface area
roll up
S. Maruyama: http://www.photon.t.u-tokyo.ac.jp/~maruyama/pvwin/pvwin-j.html
4Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Applications of Nanotubes
Field emitters for display
Biosensors
Fuel cells/ Catalyst support
Gate
Source
Drain
10 μm
Source Drain
CNT
CNT-FETsA
CNTSisub
DrainSource
Antigen Antibody
CNT
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Potential for High-Speed Devices
0
1
2
3
4
0 10 20 30 40 50 60 70 80
Ele
ctro
n D
rift V
eloc
ity (x
107 c
m/s
)
F (kV/cm)
CNT
GaAs Si
(G. Pennington et al. SISPAD’02, 279 (2002))
•1.5 times larger peak velocitythan that in GaAs
Electron velocity in NT
6Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
CNT FETsCNT FET Structure
Ti/AuCo/Pt Co/PtSiO2(100 nm)
Ti/Au
p-Si sub.+
Source Drain
Gate
CNTGrowth on patterned catalystMOS FET with a back gate
SEM image of CNT FET
PG
RPArEtOH
Mix
er
Sample
Heater
OutMFC
MFC
Position conrol
Alcohol: high-Q CNT growth
Y. Ohno et al. Jpn. J. Appl. Phys. 42, 4116
7Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
I-V Characteristics of CNT- FET
・ Mostly p-type・ ambipolar for CNTs
with small EgVGS < -15 V : p-typeVGS > 10 V : n-type
0
0.1
0.2
0.3
0.4
0.5
-20 -10 0 10 20
I D (n
A)
VGS (V)
VDS = 20 mV
23 K
T. Shimada et al. Appl. Phys. Lett. 81 4067
10-12
10-11
10-10
10-9
10-8
10-7
10-6
-10 -5 0 5 10
VDS
= -0.1 V
8Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Energy Band of CNTFETs
Schottky barrier control by gate voltageelectron / hole injection ambipolar
-I D
V GSV th_p V th_n
∝EG
Schottky barrier transistor
D
VDShole
(a) p channel
(b) OFFelectron
(c) n channel
S
T. Mizutani et al. Jpn. J. Appl. Phys. 44 1599
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ID-VGS characteristics of CNTFETs
Φm dependent I‐V characteristics.
Fermi level pinning is weak in the case of nanotubes.
p‐type Ambipolar n‐type
Y. Nosho et al. Nanotechnology 17 3412
10-12
10-11
10-10
10-9
10-8
10-7
10-6
-10 -5 0 5 10
VDS
= -0.1 V
Pd(5.1eV)
|ID| (A)
VGS (V)
h
-10 -5 0 5 1010-12
10-11
10-10
10-9
10-8
10-7
10-6
VDS
= 0.1 VMg (3.7 eV)
h
e
VGS (V)
|ID| (A)
-10 -5 0 5 1010-12
10-11
10-10
10-9
10-8
10-7
10-6
VDS
= 0.1 V
Ca (2.9 eV)
e
VGS (V)
|ID| (A)
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0
0.2
0.4
0.6
0.8
1
1.2
2 2.5 3 3.5 4 4.5 5 5.5 6
Sin-GaAsSWNT電
子に対する障壁高さφ Bn
(eV)
仕事関数 φm
(eV)
S ~ 0.05
S ~ 0.05
S ~ 0.25
( )
( )
SWNTは既存の半導体と比
べて界面特性は良好
SWNTは
フェルミレベルピニングが弱い
25.0~m
BnSφφ∂∂
=∂∂
=(仕事関数)
(障壁高さ)
φBn
注: 括弧で示した点は推定
ショットキ障壁の制御性
11Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
0
2
4
6
8
10
12
14
-1 -0.5 0 0.5 1
I (nA
)
VAK
(V)
VGK
= 0 V
Quasi pn Junction Using Different Metals
Reverse bias (VAK < 0)
Ca
Pd
Eg
VAK
Forward bias (VAK > 0)
Ca
Pdh
Eg
VAK
12Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Rc/Rch Measurements Using Multi-Terminal Devices
5 μm12
4
5
3
50 μm
Catalyst
p+-Si back gate
SiO2 (100 nm)
1 2 3 4 5
Rc Rc
Rch
Rc Rc
←
V
Rc
Rch
Rc
A
two probe four probeY. Nosho et al. Jpn. J. Appl. Phys. 46 L474
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Comparison between R2 and R4
R2 = R4 Edge contact
(c)
0
5 104
1 105
1.5 105
2 105
2.5 105
3 105
0 1000 2000 3000 4000 5000
R 2R 4
R (o
hm)
Diatance (nm)
Vg: -5 VVds or V2-V3: -50 mV
Rch
Rc
V1 V2 V3 V4
RcRch
RcRch
RcRc Rc
Rch underneath Rch underneath
(a) (b) X
14Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
p+-Si Back-gateSiO2 (100 nm)
S D
LG: 200 nm AlOX (10 nm)F4TCNQ
Catalyst
0
200
400
600
800
1000
1200
0 1 2 3 4 5
R (k
Ω)
Channel length (μm)
Device #1 Undoped
Doped
RC Reduction by Chemical DopingF4TCNQ:large electron affinity
TCNQ:tetracyano-p-quinodimethane
Soaked in F4TCNQ solutionfor 30 min. after electrode formation
Self-aligned doping
15Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
RC (kΩ) Rchan (kΩ/μm)Device
Undoed Doped Change (%)
Undoped Doped Change (%)
#1 164 11.9 -92 167 116 -30
#2 362 20.5 -94 751 627 -16
#3 118 30.9 -73 241 233 -4
#4 58.5 (-17.2) - 904 367 -59
Barrier Height Lowering
EF
EC
EVSWNTSource
(b)
++
‐‐Substrate
Source
-
F4TCNQ
-+++ -
(a)
16Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
10-11
10-10
10-9
10-8
10-7
10-6
-0.6 -0.4 -0.2 0 0.2 0.4 0.6
-I D (V
)
VTG
(V)
Doped
S D
p i p
G
Undoped
Performance Improvement by p-doping in Top-Gate CNT-FETs
VDS
(V)
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0-1-0.8-0.6-0.4-0.20
DopedUndoped
I D(μ
A)
VTG
: -1~0 V, 0.2 V step
gm=5 S/mm Y. Nosho Nanotechnology 18 415202
10 μm
Source
Top-gate
Drain
Lg=0.2 μm
17Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Grid-inserted μ-PECVD
Biases A-C : G-C =100V : 5VTemperature 650℃Gases CH4 : H2 = 2 : 80 sccmPressure 500PaPlasma Power 500W
Conditions
Suppression of ion bombardment damage
Grid insertionGrid insertion Microwave
Quartz tube
Grid
CH4 : H2
Plasma
Pump
AnodeAnode
Cathode4 mm
5 cm
Sample2mm D holes
18Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Fe(1 nm)/Ti(1 nm)/SiO2/Si
Growth time:10 m, Tsub : 600℃
200μm
Long CNTs Grown on Patterned Catalysts
Kishimoto et al. Jpn J. Appl. Phys. 44 1554
1 μm
19Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
• p-channel FETs-7-6-5-4-3-2-10
-1.5 -1 -0.5 0
I D (μ
A)
VDS
(V)
-10 ~ 2 V2 V step
VGS
:-2 V
2 V
-10 V
-7-6-5-4-3-2-10
-10 -8 -6 -4 -2 0 2 I D
(μA
) V
GS (V)
VDS
= -1.5 V
I-V Characteristics
-30
-25
-20
-15
-10
-5
0
-10 -8 -6 -4 -2 0 2 4 6
I D (μ
A)
VGS
(V)
VDS
= -1.5 V
ID max
ID min
-30
-25
-20
-15
-10
-5
0
-1.5 -1 -0.5 0
I D (μ
A)
VDS
(V)
-10 ~ 10 Vwith 2 V step
VGS
:
-10 V
Non-depletable ID:metallic CNTs
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Preferential Growth of CNTs with Semiconducting Behavior
0
1
2
3
4
5
semiconducting CNTs
metallic CNTs
1 11 21 31 41 51 61 71 81
I D (μ
A)
cumulative number of the devices
more than 96%more than 96%
21Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Kelvin Probe Force Microscopy(KFM)
Detection of atomic force
Topographic image
Detection of electrostatic force
Surface Potential image
+
Photo Diode wr
w
V Feed Back
Surface Potential
Topography
Z Feed Back
Voff
Vacsinwt
VrsinwrtCantilever
Sample
Laser Diode
*Topographic and surface potential images can be obtained simultaneously.
22Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
|VDS| = 0.3 V0
1 10-6
2 10-6
3 10-6
4 10-6
5 10-6
6 10-6
-10 -5 0 5 10
|ID| [
A]
VGS [V]
“OFF”
defect500 nm
AFM EFM EFMVGS = -1 V VGS = 2 V
“ON”
Non-uniform potential image (indicated by arrows) at the “OFF” state reflecting defects in the CNT .
Okigawa et al. ISCS 07 Kyoto, Japan
Non-uniform Potential Image
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At the OFF state: Sharp potential drops at two positions.
S: 0 VD: 0.3 V VGS = +2 V
“OFF”mV
nm700
750
800
850
900
950
1000
1050
0 500 1000 1500 2000
Potential profile along the CNT
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0
10
20
30
40
0 10 20 30 400
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
ALD PECVD
VDS:1V
VBGS:10V
VDS:1V
VBGS:10V
I D (μA
)Effect of the film deposition
I D (μ
A)
ID (before deposition) (μA)
ID (before deposition) (μA)
Little degradation of ID by ALD deposition
Y. Nakashima et al. MNC 07 Kyoto, Japan
25Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
CNT-FET Biosensor High SensitivityLabel free
S D
Antibody Antigen
S DInsulator
I D(A
)I D
(A)
-5 10-8
-4 10-8
-3 10-8
-2 10-8
-1 10-8
0
0 500 1000 1500 2000 2500 3000 3500
Time(sec)
PBS PSA
-5 10-8
-4 10-8
-3 10-8
-2 10-8
-1 10-8
0
0 500 1000 1500 2000 2500 3000 3500
Time(sec)
PBS PSA AG
K. Tani et al. Jpn. J. Appl. Phys 45 . 5481
26Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Demonstration of E/O and O/E Signal Conversions Using single SWNT
0.0 0.5 1.0 1.5 2.0 2.5 3.0
PL In
tens
ity (a
.u)
Time (sec)
VG
S (V) 1
0
E/O Conversion
O/E Conversion
0
50
0
380
0 100 200 300 400 500 600 700 800
I D (p
A)
Time (ms)
Lase
r Pow
er (μ
W)
0.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15 20 25 30 35
I D(p
A)
x (μm)
Drain
Source
A'A
y. Oho et al. Jpn J. Appl. Phys. 44 1592
27Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Prospects: Carbon Nanotube Electronics
•High-speed/Low-power integrated circuitswith high functionality
•Opto-electronic devices (FETs/emission/detection) •Biosensors
ACNTSisub
DrainSource
Antigen Antibody
28Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
炭素からなるビルトインの円筒状ナノ構造(直径 : 1nm レベル)
・加工不要(加工損傷なし):高品質・無散乱輸送:高速動作・高い電流駆動能力 → 高速動作・チャネル厚みが薄い(1nm) →短チャネル効果に強い・電子/正孔で同じ有効質量:同じ移動度
n-chとp-chで同じ特性 → CMOSに有利
カーボンナノチューブデバイスの魅力カーボンナノチューブデバイスの魅力
特長・
利点
1nm
無散乱輸送 Source Drain
CNT
Gate
29Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
CNTFETの電流利得遮断周波数
Appl. Phys. Lett. 90 (2007) 233108
10 CNTs/μmLDS=300 nm
30 GHz
30Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
Cutoff Frequency, fT
S. Hasan et al. IEEE Trans. Nanotechnology 5 (2006) 14
Ballistic condition
LG= 30 nm
4.3 THz
31Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
取り組むべき課題取り組むべき課題
CNTFET単体の直流特性は既にSi 微細MOSの2020年目標(電流駆動能
力)はクリア。しかし以下の多くの課題を有している。
半導体優先成長:100%触媒制御/直径制御指定した位置からのナノチューブの高密度配向成長(1本/20nm)触媒からの高イールド成長:100%
低抵抗コンタクト制御表面保護膜・極薄ゲート絶縁膜(HfO2 3nm (SiO2換算膜厚0.5nm)レベル)ドーピング技術CNTチャネル内欠陥・ばらつきの評価・解析と低減高速動作実証
プロセス・デバイス技術
成長技術
ID=4-25μA/nm, gm=5-17μS/nm
32Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演 水谷
課題解決に向けたアプローチ課題解決に向けたアプローチ
極微細ゲート形成技術
高周波特性評価技術
石英基板を用いた配向成長低誘電率→高周波動作に最適
ドーピングによる寄生抵抗の低減
高周波特性評価デバイス開発
Sパラメータ測定による遅延時間評価解析、
応答速度支配要因解明、雑音特性評価解析
セルフアラインプロセスの開発
低損傷ゲート絶縁膜形成:原子層堆積技術