1. Tamer Ragheb ELEC 527 Presentation Rice University 3/15/2007
Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution and Applications for Future Nanoscale ICs
Tamer Ragheb
ELEC 527 Presentation
Rice University
3/15/2007

2. 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
I think you have this slide covered.
Hoenlein et al., Materials Science and Engineering: C, 2003

3. 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
I think you have this slide covered.
Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp , 2003

4. 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
I think you have this slide covered.
Tans et al., Nature, vol. 393, pp , 1998
Hoenlein et al., Materials Science and Engineering: C, 2003

5. 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
I think you have this slide covered.
Tans et al., Nature, vol. 393, pp , 1998

6. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
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
Enhanced-mode p-type FET
n-type FET
I think you have this slide covered.
Bachthold et al., Science, vol. 294, pp , 2001

7. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Bachthold et al. simulated circuits:
I think you have this slide covered.
Bachthold et al., Science, vol. 294, pp , 2001

8. 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 gate segments
Each segment is individually biased for more behavior control
I think you have this slide covered.
Wind et al., Physical Review Letters, vol. 91, no. 5, 2003

9. 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)
I think you have this slide covered.
Yang et al., Applied Physical Letters, vol. 88, p , 2006

10. 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
I think you have this slide covered.
Yang et al., Applied Physical Letters, vol. 88, p , 2006

11. 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
I think you have this slide covered.
Derycke et al., Nano Letters, vol. 1, no. 9, pp , 2001

12. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
The inverter fabrication steps:
I think you have this slide covered.
Derycke et al., Nano Letters, vol. 1, no. 9, pp , 2001

13. 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
I think you have this slide covered.
Javey et al., Nano Letters, vol. 2, no. 9, pp , 2002

14. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Javey et al.’s circuits:
I think you have this slide covered.
Javey et al., Nano Letters, vol. 2, no. 9, pp , 2002

15. 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
I think you have this slide covered.
Chen et al., Science, vol. 311, p. 1735, 2006

16. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Chen et al.’s circuit is a voltage controlled (Vdd) ring oscillator
Vdd=0.92V
Vdd=0.5V
I think you have this slide covered.
Chen et al., Science, vol. 311, p. 1735, 2006

17. 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
I think you have this slide covered.
Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp , 2003

18. 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
I think you have this slide covered.
Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp , 2003

19. 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.
I think you have this slide covered.
Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp , 2006
Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp , 2006

20. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Chen et al. used plasma treatment to convert metallic CNT to semiconductor type.
I think you have this slide covered.
Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp , 2006

21. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Na et al. used protein-coated nanoparticles in the contact areas to convert metallic CNT to semiconductor type.
Measured values
Theoretically
I think you have this slide covered.
Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp , 2006

22. 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
I think you have this slide covered.
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 , 2004

23. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Liang et al.’s CNTFET simulation results:
I think you have this slide covered.
Liang et al., Physica. E, low-dimentional systems and nanostructures, vol. 23, no. 1-2, pp , 2004

24. 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
I think you have this slide covered.
Cui et al., Applied Physics Letters, vol. 81, no. 17, pp , 2002

25. 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
I think you have this slide covered.
Cui et al., Applied Physics Letters, vol. 81, no. 17, pp , 2002

26. 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
I think you have this slide covered.
Lu et al., Applied Physics Letters, vol. 88, p , 2006

27. Short Channel CNTFET (Sub-20nm)
Seidel et al. proposed a fabrication method to obtain CNTFET with sub-20nm long channels
I think you have this slide covered.
Seidel et al., Nano Letters, vol. 5, no. 1, pp , 2005

28. 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
I think you have this slide covered.
Cui et al., Nano Letters, vol. 2, no. 2, pp , 2002

29. 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
I think you have this slide covered.
Shimotani et al., Applied Physics Letters, vol. 88, p , 2006

30. 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
I think you have this slide covered.
Zhang et al., Applied Physics Letters, vol. 88, p , 2006

31. RF Measurement circuitry
CNTFET in RF Circuits
Zhang et al. measured the RF performance of CNTFETs
RF Measurement circuitry
Measurement results
I think you have this slide covered.
Zhang et al., IEEE Electron Device Letters, vol. 27, no. 8, pp , 2006

32. CNTFET in RF Circuits
Zhang et al. proposed an RF simple model for CNTFET
I think you have this slide covered.
Zhang et al., IEEE Electron Device Letters, vol. 27, no. 8, pp , 2006

33. CNTFET in RF Circuits
Pesetski et al. employed CNTFET to build RF circuits that can operate up to 23GHz
I think you have this slide covered.
Pesetski et al., Applied Physics Letters, vol. 88, p , 2006

34. CNTFET Built on Insulator
Liu et al. succeeded to build a novel nanotube-on-insulator (NOI) CNTFET similar to silicon-on-insulator (SOI) technology
I think you have this slide covered.
Liu et al., Nano Letters, vol. 6, no. 1, pp , 2006

35. CNTFET Built on Insulator
Liu et al. built NOI transistors with:
Top-gated
Polymer-electrolyte-gated
I think you have this slide covered.
Liu et al., Nano Letters, vol. 6, no. 1, pp , 2006

36. 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
I think you have this slide covered.

37. References (in Order of Appearance)
Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp , 2003
Tans et al., Nature, vol. 393, pp , 1998
Bachthold et al., Science, vol. 294, pp , 2001
Wind et al., Physical Review Letters, vol. 91, no. 5, 2003
Yang et al., Applied Physical Letters, vol. 88, p , 2006
Derycke et al., Nano Letters, vol. 1, no. 9, pp , 2001
Javey et al., Nano Letters, vol. 2, no. 9, pp , 2002
Chen et al., Science, vol. 311, p. 1735, 2006
Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp , 2006
Na et al., Fullerenes, Nanotubes, and Carbon Nanostructures, vol. 14, pp , 2006
Liang et al., Physica. E, low-dimentional systems and nanostructures, vol. 23, no. 1-2, pp , 2004
Cui et al., Applied Physics Letters, vol. 81, no. 17, pp , 2002
Lu et al., Applied Physics Letters, vol. 88, p , 2006
Seidel et al., Nano Letters, vol. 5, no. 1, pp , 2005
Cui et al., Nano Letters, vol. 2, no. 2, pp , 2002
Shimotani et al., Applied Physics Letters, vol. 88, p , 2006
Zhang et al., Applied Physics Letters, vol. 88, p , 2006
Pesetski et al., Applied Physics Letters, vol. 88, p , 2006
Liu et al., Nano Letters, vol. 6, no. 1, pp , 2006

38. Thank You Acknowledgments: Prof. James M. Tour and Prof. Lin Zhong
Colleagues in RAND group
Colleagues in the ELEC 527 class

39. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution
Chen et al. used plasma treatment to convert metallic CNT to semiconductor type.
Not usable CNTs
I think you have this slide covered.
Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp , 2006