カーボンナノチューブFETの現状と将来展望水谷孝 …semicon.jeita.or.jp/STRJ/STRJ/2007/6H_WS2007special...R2 = R4 Edge contact (c) 0 5 104 1 105 1.5 105 2 105 2.5

1Work in Progress - Do not publish STRJ WS: March6, 2008, 特別講演水谷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


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


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


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


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


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


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


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


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)


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


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


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


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


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


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)


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


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


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


• 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


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%


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.


|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


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


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


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


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


Prospects: Carbon Nanotube Electronics

•High-speed/Low-power integrated circuitswith high functionality

•Opto-electronic devices (FETs/emission/detection) •Biosensors

ACNTSisub

DrainSource

Antigen Antibody


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


CNTFETの電流利得遮断周波数

Appl. Phys. Lett. 90 (2007) 233108

10 CNTs/μmLDS=300 nm

30 GHz


Cutoff Frequency, fT

S. Hasan et al. IEEE Trans. Nanotechnology 5 (2006) 14

Ballistic condition

LG= 30 nm

4.3 THz


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


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

Documents

カーボンナノチューブFETの現状と将来展望 水谷孝 …semicon.jeita.or.jp/STRJ/STRJ/2007/6H_WS2007special...R2 = R4 Edge contact (c) 0 5 104 1 105 1.5 105 2 105 2.5

カーボンナノチューブFETの現状と将来展望水谷孝 …semicon.jeita.or.jp/STRJ/STRJ/2007/6H_WS2007special...R2 = R4 Edge contact (c) 0 5 104 1 105 1.5 105 2 105 2.5