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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. Conventional Semiconductor Microelectronics Will Come to an End. Vertical Scaling. Lateral Scaling.

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Tamer Ragheb ELEC 527 Presentation Rice University 3/15/2007

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  1. 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 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

  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 Hoenlein et al., Materials Science and Engineering: C, vol. 23, no. 8, pp. 663-669, 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 Tans et al., Nature, vol. 393, pp. 49-52, 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 Tans et al., Nature, vol. 393, pp. 49-52, 1998

  6. 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

  7. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution • Bachthold et al. simulated circuits: Bachthold et al., Science, vol. 294, pp. 49-52, 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 4 gate segments • Each segment is individually biased for more behavior control 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) Yang et al., Applied Physical Letters, vol. 88, p. 113507, 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 Yang et al., Applied Physical Letters, vol. 88, p. 113507, 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 Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 2001

  12. Carbon Nanotube Field-Effect Transistors (CNTFETs): Evolution • The inverter fabrication steps: Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 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 Javey et al., Nano Letters, vol. 2, no. 9, pp. 929-932, 2002

  14. 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

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

  16. 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

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

  20. 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

  21. 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

  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 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

  23. 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

  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 Cui et al., Applied Physics Letters, vol. 81, no. 17, pp. 3260-3262, 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 Cui et al., Applied Physics Letters, vol. 81, no. 17, pp. 3260-3262, 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 Lu et al., Applied Physics Letters, vol. 88, p. 113104, 2006

  27. 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

  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 Cui et al., Nano Letters, vol. 2, no. 2, pp. 117-120, 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 Shimotani et al., Applied Physics Letters, vol. 88, p. 073104, 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 Zhang et al., Applied Physics Letters, vol. 88, p. 123112, 2006

  31. 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

  32. 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

  33. 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

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

  35. 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

  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

  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

  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 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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