carbon nanotube field-effect transistors (cntfets): evolution and applications for future nanoscale...

Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution and Applications

for Future Nanoscale ICs

Tamer Ragheb

ELEC 527 Presentation

Rice University

3/15/2007

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Conventional Semiconductor Microelectronics Will Come to an End

Conventional semiconductor device scaling obstacles: Diffusion areas will no longer be

separated by a low doped channel region

Equivalent gate oxide thickness will fall below the tunneling limit

Lithography costs will increase exponentially

Solution:Find new technologies such as

molecular electronics and CNT

Lateral Scaling

Vertical Scaling

Hoenlein et al., Materials Science and Engineering: C, 2003

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Why Carbon Nanotubes (CNTs)?

CNTs exhibit remarkable electronic and mechanical characteristics due to:Extraordinary strength of the carbon-carbon bondThe small atomic diameter of the carbon atomThe availability of free π-electrons in the graphitic

configuration

Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp. 663-669, 2003

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Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

Most of the CNTFETs employ:Semiconductor Single-walled carbon nanotube (SWCNT)

as the channelThe contacts of SWCNT are the source and drain regionsA gate plate to control the conduction behavior of SWCNT

Tans et al. reported the first CNTFET (1998)Used SWCNT as a channelPlatinum (Pt) as contactsSilicon (Si) as a back-gate

Tans et al., Nature, vol. 393, pp. 49-52, 1998Hoenlein et al., Materials Science and Engineering: C, 2003

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Tans at al.’s CNTFET exhibits p-type FET behavior

Tans et al. succeeded to modulate the conductivity over more than 5 orders of magnitude

The problem was the thick oxide layer used Tans et al., Nature, vol. 393, pp. 49-52, 1998

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Bachthold et al. replaced:The Si-back gate by a patterned Al-gateThe thick SiO2 layer by a thin Al2O3 layerPlatinum (Pt) contacts by gold (Au)

The gate biasing can change the behavior from p-type to n-type

Bachthold at al. succeeded to build different logic gates using the p-type behavior

Bachthold et al., Science, vol. 294, pp. 49-52, 2001

Enhanced-mode p-type

FET

n-type FET

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Bachthold et al. simulated circuits:

Bachthold et al., Science, vol. 294, pp. 49-52, 2001

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Due to difficulty of back gate biasing, Wind et al. proposed the first CNTFET with top gate

The top gate is divided into 4 gate segments

Each segment is individually biased for more behavior control

Wind et al., Physical Review Letters, vol. 91, no. 5, 2003

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Top-gated CNTFETs allow:Local gate biasing at low voltageHigh speed switchingHigh integration density

Yang et al. compared the performance of:Bottom-gate without top oxideBottom-gate with top oxideTop-gate with top oxide

The top oxide used is TiO2 (high-k dielectric)

Yang et al., Applied Physical Letters, vol. 88, p. 113507, 2006

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Yang et al. proved that:Top gate reduces the hysteresis behavior of CNTFETTop gate reduces the needed gate voltage

Yang et al., Applied Physical Letters, vol. 88, p. 113507, 2006

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Derycke et al. proposed the first CMOS-like device by producing n-type CNTFETs by:Annealing in a vacuum at 700KDoping with potassium (K)

Derycke et al. succeeded to build the first CMOS-like inverter

Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 2001

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The inverter fabrication steps:

Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 2001

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Javey et al. proposed converting p-type into n-type by field manipulation

Javay et al. succeeded to build different logic gates

Javey et al., Nano Letters, vol. 2, no. 9, pp. 929-932, 2002

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Javey et al.’s circuits:

Javey et al., Nano Letters, vol. 2, no. 9, pp. 929-932, 2002

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Chen et al. proposed a complete integrated logic circuit assembled on a single CNT

They controlled the polarities of the FETs by using metals with different work functions as the gates

Chen et al., Science, vol. 311, p. 1735, 2006

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Chen et al.’s circuit is a voltage controlled (Vdd) ring oscillator

Chen et al., Science, vol. 311, p. 1735, 2006

Vdd=0.92VVdd=0.5V

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Hoenlein et al. proposed a vertical CNTFET (VCNTFET), it consists of:1nm diameter 10nm long SWCNTA coaxial gate and a gate dielectric with 1nm thickness


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VCNTFET has the advantages of:Vertical growth in CNT is much easier and aligned than

horizontal growth3D connections can be used in the vertical configuration


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All the previous structures depend on semiconductor SWCNT.

SWCNT available commercially contain about 33-60% metallic CNTs.

For mass production and high yield, methods have to be found to guarantee that CNTFETs use semiconductor type SWCNTs.

Chen et al. and Na et al. proposed 2 different methods to convert metallic CNTs into semiconductor type.

Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp. 3680-3685, 2006Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp. 141-149, 2006

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Chen et al. used plasma treatment to convert metallic CNT to semiconductor type.

Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp. 3680-3685, 2006

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Na et al. used protein-coated nanoparticles in the contact areas to convert metallic CNT to semiconductor type.

Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp. 141-149, 2006

Measured values

Theoretically

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Liang et al. proposed building CNTFET using a double-walled CNT (DWCNT)The inner-shell is the gate due to its low conductanceThe outer-shell is the channel due to its high conductanceIt is easy to fabricate high-quality DWCNT

In fabrication:Cover the outer-shell partially

by polymer-patternsThe exposed part can be

etched by H2O or O2 plasma at room temperature

Liang et al., Physica. E, low-dimentional systems and nanostructures, vol. 23, no. 1-2, pp. 232-236, 2004

Router=1.73nm

Rinner=1.39nm

Inter-shell separation=0.34nm

Pd contacts

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Liang et al.’s CNTFET simulation results:

Liang et al., Physica. E, low-dimentional systems and nanostructures, vol. 23, no. 1-2, pp. 232-236, 2004

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CNTFET as Memory Devices

Cui et al. employed CNTFET charge storage behavior to build a non-volatile memory

The memory device is stable to hold the data over a period of at least 12 days in the ambient conditions

Cui et al., Applied Physics Letters, vol. 81, no. 17, pp. 3260-3262, 2002

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To avoid the probability of metallic CNT, Cui et al. used two methods:Annealing (to heat at 335K for different periods)Controlled oxygen plasma treatment at room temperature

Cui et al., Applied Physics Letters, vol. 81, no. 17, pp. 3260-3262, 2002

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Lu et al. proposed a non-volatile flash memory device using:CNTs as floating gatesHfAlO as control/tunneling oxidePlatinum (Pt) as top electrodes

CNT insertion enhances the memory behavior by holes trapping

Lu et al., Applied Physics Letters, vol. 88, p. 113104, 2006

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Short Channel CNTFET (Sub-20nm)

Seidel et al. proposed a fabrication method to obtain CNTFET with sub-20nm long channels

Seidel et al., Nano Letters, vol. 5, no. 1, pp. 147-150, 2005

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Single Electron CNTFET

Cui et al. fabricated single electron CNTFET (quantum dot) with a length of 10nm

The observed differential conductance peaks are a clear signature of single electron tunneling in the device

Cui et al., Nano Letters, vol. 2, no. 2, pp. 117-120, 2002

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Electro-Chemical CNTFET

Shimotani et al. studied another kind of CNTFET, which is electro-chemical CNTFET

In this transistor the gate is the electrolyte solution

Shimotani et al., Applied Physics Letters, vol. 88, p. 073104, 2006

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CNTFET as a Chemical Sensor

CNTFETs are very sensitive devices to chemicals. Zhang et al. studied the sensing mechanism of

CNTFET to NO2 and NH3 CNT body is more sensitive to ammoniaCNT contacts are more sensitive to NO2

Zhang et al., Applied Physics Letters, vol. 88, p. 123112, 2006

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CNTFET in RF Circuits

Zhang et al. measured the RF performance of CNTFETs

Zhang et al., IEEE Electron Device Letters, vol. 27, no. 8, pp. 668-670, 2006

RF Measurement circuitry

Measurement results

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Zhang et al. proposed an RF simple model for CNTFET

Zhang et al., IEEE Electron Device Letters, vol. 27, no. 8, pp. 668-670, 2006

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Pesetski et al. employed CNTFET to build RF circuits that can operate up to 23GHz

Pesetski et al., Applied Physics Letters, vol. 88, p. 113103, 2006

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CNTFET Built on Insulator

Liu et al. succeeded to build a novel nanotube-on-insulator (NOI) CNTFET similar to silicon-on-insulator (SOI) technology

Liu et al., Nano Letters, vol. 6, no. 1, pp. 34-39, 2006

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CNTFET Built on Insulator

Liu et al. built NOI transistors with:Top-gated

Polymer-electrolyte-gated

Liu et al., Nano Letters, vol. 6, no. 1, pp. 34-39, 2006

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Conclusions

CNT is a future replacement for semiconductor based microelectronics

The evolution of CNTFET is discussed Employing CNTFET in a lot of applications such as:

Logic circuitsMemoriesChemical sensorsRF circuits

Integrating CNT based interconnects with devices can produce a complete future nanoscale ICs

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References (in Order of Appearance)

Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp. 663-669, 2003 Tans et al., Nature, vol. 393, pp. 49-52, 1998 Bachthold et al., Science, vol. 294, pp. 49-52, 2001 Wind et al., Physical Review Letters, vol. 91, no. 5, 2003 Yang et al., Applied Physical Letters, vol. 88, p. 113507, 2006 Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 2001 Javey et al., Nano Letters, vol. 2, no. 9, pp. 929-932, 2002 Chen et al., Science, vol. 311, p. 1735, 2006 Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp. 3680-3685, 2006 Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp. 141-149, 2006 Liang et al., Physica. E, low-dimentional systems and nanostructures, vol. 23, no. 1-2, pp.

232-236, 2004 Cui et al., Applied Physics Letters, vol. 81, no. 17, pp. 3260-3262, 2002 Lu et al., Applied Physics Letters, vol. 88, p. 113104, 2006 Seidel et al., Nano Letters, vol. 5, no. 1, pp. 147-150, 2005 Cui et al., Nano Letters, vol. 2, no. 2, pp. 117-120, 2002 Shimotani et al., Applied Physics Letters, vol. 88, p. 073104, 2006 Zhang et al., Applied Physics Letters, vol. 88, p. 123112, 2006 Pesetski et al., Applied Physics Letters, vol. 88, p. 113103, 2006 Liu et al., Nano Letters, vol. 6, no. 1, pp. 34-39, 2006

Thank You

Acknowledgments:Prof. James M. Tour and Prof. Lin Zhong

Colleagues in RAND group

Colleagues in the ELEC 527 class

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Chen et al. used plasma treatment to convert metallic CNT to semiconductor type.

Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp. 3680-3685, 2006

Not usable CNTs

carbon nanotube field-effect transistors (cntfets): evolution and applications for future nanoscale...

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