Carbon Nanotube Field-Effect Transistors (CNTFETs)tiiciiitm.com/profanurag/STNE-3.1.pdf ·...

Carbon Nanotube Field-Effect Transistors (CNTFETs)

Anurag Srivastava

4/06/2017

4/37

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

5/37

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

6/37

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

7/37


• 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

8/37


• 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

Enhanced-mode p-type

FET

n-type FET

9/37


• Bachthold et al. simulated circuits:

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

10/37


• 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

11/37


• 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

12/37


• 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

13/37


• 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

14/37


• The inverter fabrication steps:

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

15/37


• 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

16/37


• Javey et al.’s circuits:

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

17/37


• 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

18/37


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

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

Vdd=0.92V Vdd=0.5V

19/37


• 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


20/37


• 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


21/37


• 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

22/37


• 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

23/37


• 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

24/37


• 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

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

25/37


• 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

26/37

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

27/37

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

28/37

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

29/37

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

30/37

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

31/37

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

32/37

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

33/37

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

34/37

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

35/37

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

36/37

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

37/37

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

38/37

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

39/37

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

40/37


• 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

CNTs for Digital Logics: Materials Challenge

Carbon Nanotube Field-Effect Transistors (CNTFETs)tiiciiitm.com/profanurag/STNE-3.1.pdf ·...

Documents

Transcript of Carbon Nanotube Field-Effect Transistors (CNTFETs)tiiciiitm.com/profanurag/STNE-3.1.pdf ·...