©2006 university of california prepublication data march 2006 in-situ controlled growth of carbon...

©2006 University of California Prepublication Data March 2006

In-situ Controlled Growth of Carbon Nanotubesby Local Synthesis

Researchers Takeshi Kawano and Michael ChoAdvisor Professor Liwei Lin

Berkeley Sensor & Actuator Center

[email protected]


Outline

Background

Motivation

Experimental procedure

In-situ monitoring of CNT connection

Self-assembled single CNT

CNT/Si junction and contact resistance

Electrical properties of Si/CNT/Si system

“Carbon nanotube-based nanoprobe electrode”

Summary


Background – Carbon nanotube –

CNT-based nanomotor

A. Zettl Gr., Nature, 424, 408 (2003)

IC integrated CNT

H. Dai Gr., Nano Letters, 4, 1 (2004)

CNT-based bio-probe

M. Lieber Gr., Nature, 394, 52 (1998).

Nanotube oscillator

P. L. EcEuen Gr., Nature, 431, 284 (2004).


Motivation

CMOS integration of nano structures

(carbon nanotubes (CNTs))

Local and selective synthesis

using silicon microstructures (MEMS)

Device applications to nano sensors and

nano electronics

1. In-situ controlled growth of CNT 2. Assembly of single CNT3. CNT/silicon contact discussed


Experimental Procedure

Electric field assisted synthesis

Gaps between Si structures

Bias between Si (V2 )

Electric field (V2 / gaps)

5 ~ 10 m 2 ~ 5 V

0.2 ~ 1 V/m

Temperature

C2H2/Ar gasSynthesis pressure

850 ~ 900C 60 / 55 sccm

250 Torr

Local synthesis of CNT


In-Situ Monitoring of CNT Connection

RV

VVVR

R

V

R

VVVI

OutT

OutCNT

Out

CNT

Out

)(

)(

21

21


I-V Curves of Silicon/CNT/Silicon System

2.5 M

Nanotube Diameter 50nm Length 10.3m


Carbon Nanotube-based Nanoprobe Electrode

Outline

Background – Nanoprobe for cell/neuron –

Motivation

Biocompatible insulator for CNT

Process sequence

Images of CNT probes

Electrical properties of CNT probe


Background – Nanoprobe for cell/neuron –

AFM with NanoneedleI. Obataya, C. Nakamura, S. HanN. Nakamura, J. Miyake, Nano Letters, 5, 1 (2005).

Multi-functional ProbeS. Nagasawa, H. Arai, R. Kanzaki, I. Shimoyama,Proc. of Transducers’05, 1230 (2005).

Microprobe devices for neuronal tissue

From J. Donoghue, Nature Neuroscience, 5, pp1085 (2002)

DiameterNeural Activity Extracellular IntracellularFrequency

5 ~ 10 m

100 V100 mV

DC10 kHz

Properties of Neuron


Motivation Carbon nanotube based nanoprobe electrode Low invasive Intracellular probe for potential recording Intracellular probe for chemical detector


Biocompatible Insulator for CNT– Parylene-C –

CNT encapsulated with Parylene TEM image (50nm-thick Parylene)

Parylene-C Properties & Characteristics CVD(chemical vapor deposition) at Room temp.

High electrical resistivity (~1016 -cm)

Biocompatible material

Conformal fashion and pinhole free


Process Sequence

Process sequence

SEM images(a) As-grown single CNT between silicon structures(b) After Parylene deposition, (c) After tip expose(d) Close-up view of the exposed tip in (c)


TEM Image of CNT Probe

TEM image of a single CNT

Outside: 50-nm-thick Parylene-C. Inside: 10-nm-diameter CNT


Layout of MEMS structure for CNT probe

Future Work

“In-situ Controlled Growth of Carbon Nanotubes by Local Synthesis”

Contact issue ( metal contact with tungsten, gold electrode)

More real-time growth measurements

Investigation of the IC-compatibility

“Carbon Nanotube-based Nanoprobe Electrode”

Impedance measurement of CNT probe

Penetration into cells (first with Onion cells)

Recording of biological signal from cell/neuron


Summary“In-situ Controlled Growth of Carbon Nanotubes by Local Synthesis” In-situ controlled synthesis of CNT using MEMS structures Bias 2 ~ 5 V, gaps between Si structures 5 ~ 10 m (E-field 0.2 ~ 1 V/m) Instant of the CNT connection monitored (growth time is 8 ~ 50 seconds) Single CNT connection controlled by the in-situ monitoring system Electrical properties of Si/CNT/Si system and CNT/Si junction CNT/Si contact resistance discussed with metal/Si junction model Overall resistance of the single CNT is 2.5 M

“Carbon Nanotube-based Nanoprobe Electrode” Device concept proposed Carbon nanotube electrode for intracellular recording Low-invasive probe and low-damage to cell/neuron Fabrication and experimental results Parylene-C deposited (50~100nm-thick), CNT tip exposed, I-V measured


Background – Carbon nanotube –CNT probe in chemistry and biologyM. Lieber Gr., Nature, 394, 2 (1998).

chemically modified nanotube tips detecting specific chemical and biological groups.

SWNT poly-Si inter connection 875C CVD

Silicon MOS-compatibilityY. Tseng, et al., Nano Letters, 4, 1 (2004).

Gas detection sensorNASA SWNTs between two electrodes

Interaction between gas molecules and CNT. Electrical signal observation, such as I or V.Tested gases: NO2 , NH3 , etc.

http://www.nasa.gov/centers/ames/research/technology-onepagers/gas_detection.html


I-V Curves of Silicon/CNT/Silicon System

Number of CNTsDiameterLength Overall resistance

Properties of CNT

950 3 nm

8.8 m (Average)480 k

Number of CNTsDiameterLength Overall resistance

Properties of CNT

150 nm

10.3 m2.5 M


Layout of MEMS structure for CNT probe

Future Work

“In-situ Controlled Growth of Carbon Nanotubes by Local Synthesis”

Contact issue ( metal contact with tungsten, gold electrode)

More real-time growth measurements

Investigation of the IC-compatibility

“Carbon Nanotube-based Nanoprobe Electrode”

Impedance measurement of CNT probe

Penetration into cells (first with Onion cells)

Recording of biological signal from cell/neuron


Self-Assembled Single CNTs(a) (b)

(c) (d)

Synthesis parameters

Gaps

Bias V1

Bias V2

8 m 7.5 V2.5 V


CNT-Silicon Heterojunction

CNT : Work function of CNT

Si: Electron affinity of silicon

Eg-Si : Band gap of silicon

Ei -EF : Fermi level for silicon

Bp: Barrier height

Bp = ( S

+ Eg-Si ) - CNT

= 0.37~0.67 eV

CNT: multiwall CNT (root and tip growth)Si: p+type, conc. 1019/cm3

Contact resistanceSpecific contact resistivity C : 10-5~10-4 -cm2 [1]

Barrier height Bp : 0.4 eV

Concentration of Silicon:1019 /cm3(p-type)

Contact area A : 2 10 -11 cm2

Diameter of CNT : 50nm

Contact resistance = 0.5 ~ 5M

AR C

Contact

[1] K. K. Ng and R. Liu, IEEE Trans. ED, 37, 1535 (1990)


Electrical Properties of CNT Probe

I-V measurement(a) Setup for the measurement (Au electrode)(b) SEM image of CNT(d) I-V curves of CNT (CNT: 22m-length and 30nm-diameter)


I would like to thank Lei Luo, Sha Li, Brian Sosnowchik for their

insightful discussions, especially Brian’s contribution for the I-V

measurement and voltage acquisition interface, and other Lab

mates. And I would like to thank staff at the EML (Electron

Microscopy Laboratory) at UC Berkeley, for their TEM work.

Acknowledgements

©2006 university of california prepublication data march 2006 in-situ controlled growth of carbon...

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