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Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution and Applications for Future Nanoscale ICs. Tamer Ragheb ELEC 527 Presentation Rice University 3/15/2007. Conventional Semiconductor Microelectronics Will Come to an End. Vertical Scaling. Lateral Scaling.

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Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution and Applications for Future Nanoscale ICs

Tamer Ragheb

ELEC 527 Presentation

Rice University

3/15/2007


Conventional Semiconductor Microelectronics Will Come to an End

Vertical Scaling

Lateral Scaling

  • 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

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


Why Carbon Nanotubes (CNTs)?

  • CNTs exhibit remarkable electronic and mechanical characteristics due to:

    • Extraordinary strength of the carbon-carbon bond

    • The small atomic diameter of the carbon atom

    • The 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Most of the CNTFETs employ:

    • Semiconductor Single-walled carbon nanotube (SWCNT) as the channel

    • The contacts of SWCNT are the source and drain regions

    • A gate plate to control the conduction behavior of SWCNT

  • Tans et al. reported the first CNTFET (1998)

    • Used SWCNT as a channel

    • Platinum (Pt) as contacts

    • Silicon (Si) as a back-gate

Tans et al., Nature, vol. 393, pp. 49-52, 1998

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

n-type FET

Enhanced-mode p-type FET

  • Bachthold et al. replaced:

    • The Si-back gate by a patterned Al-gate

    • The thick SiO2 layer by a thin Al2O3 layer

    • Platinum (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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Bachthold et al. simulated circuits:

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Top-gated CNTFETs allow:

    • Local gate biasing at low voltage

    • High speed switching

    • High integration density

  • Yang et al. compared the performance of:

    • Bottom-gate without top oxide

    • Bottom-gate with top oxide

    • Top-gate with top oxide

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

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Yang et al. proved that:

    • Top gate reduces the hysteresis behavior of CNTFET

    • Top gate reduces the needed gate voltage

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Derycke et al. proposed the first CMOS-like device by producing n-type CNTFETs by:

    • Annealing in a vacuum at 700K

    • Doping 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • The inverter fabrication steps:

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Javey et al.’s circuits:

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

Vdd=0.5V

Vdd=0.92V

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

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Hoenlein et al. proposed a vertical CNTFET (VCNTFET), it consists of:

    • 1nm diameter 10nm long SWCNT

    • A coaxial gate and a gate dielectric with 1nm thickness

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • VCNTFET has the advantages of:

    • Vertical growth in CNT is much easier and aligned than horizontal growth

    • 3D connections can be used in the vertical configuration

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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, 2006

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

Measured values

Theoretically

  • 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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • Liang et al. proposed building CNTFET using a double-walled CNT (DWCNT)

    • The inner-shell is the gate due to its low conductance

    • The outer-shell is the channel due to its high conductance

    • It is easy to fabricate high-quality DWCNT

  • In fabrication:

    • Cover the outer-shell partially by polymer-patterns

    • The exposed part can be etched by H2O or O2 plasma at room temperature

Pd contacts

Router=1.73nm

Rinner=1.39nm

Inter-shell separation=0.34nm

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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

  • 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


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


CNTFET as Memory Devices

  • 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


CNTFET as Memory Devices

  • Lu et al. proposed a non-volatile flash memory device using:

    • CNTs as floating gates

    • HfAlO as control/tunneling oxide

    • Platinum (Pt) as top electrodes

  • CNT insertion enhances the memory behavior by holes trapping

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


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


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


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


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 ammonia

    • CNT contacts are more sensitive to NO2

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


CNTFET in RF Circuits

  • Zhang et al. measured the RF performance of CNTFETs

RF Measurement circuitry

Measurement results

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


CNTFET in RF Circuits

  • 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


CNTFET in RF Circuits

  • 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


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


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


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 circuits

    • Memories

    • Chemical sensors

    • RF circuits

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


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


Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution

Not usable CNTs

  • 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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