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 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

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. 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 I think you have this slide covered. 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 I think you have this slide covered. Tans et al., Nature, vol. 393, pp. 49-52, 1998

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. 49-52, 2001

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. 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 I think you have this slide covered. 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) I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. Derycke et al., Nano Letters, vol. 1, no. 9, pp. 453-456, 2001

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

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

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. 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 I think you have this slide covered. 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. I think you have this slide covered. 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. I think you have this slide covered. Chen et al., Japanese Journal of Applied Physics, vol. 45, no. 4B, pp. 3680-3685, 2006

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. 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 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. 232-236, 2004

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. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered. Zhang et al., Applied Physics Letters, vol. 88, p. 123112, 2006

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. 668-670, 2006

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. 668-670, 2006

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. 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 I think you have this slide covered. 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 I think you have this slide covered. 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 I think you have this slide covered.

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 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. 3680-3685, 2006