TECHNIQUES OF SYNTHESIZING CARBON

NANOTUBE FETS FOR INTEGRATED CIRCUITS

GAO, FengS.I.D 20219798

PART I. NANOTUBE PLACEMENT

PART II. COMPLEMENTARY DEVICES

PART III. IMPERFECTION REMEDY

2. Deposit NMPI (Self Aligned)

1. Pattern SiO2 /HfO substrate

4. Ion exchange reaction

3. Aqueous CNT solutions preparation

Self-Assembly Approach[1,2]

NANOTUBE PLACEMENT

[1] Park, Hongsik, et al. "High-density integration of carbon nanotubes via chemical self-assembly." Nature nanotechnology 7.12 (2012): 787-791.[2] Wu, Justin, et al. "Top‐Down Patterning and Self‐Assembly for Regular Arrays of Semiconducting Single‐Walled Carbon Nanotubes." Advanced Materials 26.35 (2014): 6151-6156.

Dielectrophoresis[3]

NANOTUBE PLACEMENT

[3] Shekhar, Shashank, Paul Stokes, and Saiful I. Khondaker. "Ultrahigh density alignment of carbon nanotube arrays by dielectrophoresis." ACS nano 5.3 (2011): 1739-1746.

CNT density controlled by solution concentration ranges from 0.5 – 30 SWNT/μm

1. Pre-pattern electrodes

2. Oxygen plasma cleaning

3. DEP with DC 5 Vpp at 300kHz for 30s

4. Blown dry by N2 gas

NANOTUBE PLACEMENTTransfer Approach (Langmuir–Schaefer Method)[4]

• Semiconductor CNT purity: 99%

• CNT density: 500 tubes/μm (full converage)

[4] Cao, Qing, et al. "Arrays of single-walled carbon nanotubes with full surface coverage for high - performance electronics." Nature nanotechnology 8. 3 (2013): 180 - 186.

Controlled Growth[5]

NANOTUBE PLACEMENT

[5] Papadopoulos, Chris, and Badr Omrane. "Nanometer‐scale Catalyst Patterning for Controlled Growth of Individual Single‐walled Carbon Nanotubes." Advanced Materials 20.7 (2008): 1344-1347.

1. Pattern catalyst

2. Grow CNT3. Fabricate electrodes and gates

COMPLEMENTARY DEVICES1. Contact Controlled Devices Type[6]

High Work Function Metal

(Pd, Au)

Femi Level Near to

Valence Band

p-FET

Low Work Function Metal

(Sc, Y, Er)

Femi Level Near to

Conduction Band

n-FET

• Problem: Low work function metals are readily oxidized• Solution: Cover with inert metal and passivation layer

[6] Han, S-J., et al. "Carbon nanotube complementary logic based on erbium contacts and self-assembled high purity solution tubes." IEEE Int. Electron Dev. Meet 19 (2013): 1-19.

COMPLEMENTARY DEVICES

2. Dielectric Controlled Device Type[7]

3. Chemical Doping for n-FET[8]n-FETp-FET

[7] Franklin, Aaron D., et al. "Carbon nanotube complementary wrap-gate transistors." Nano letters 13.6 (2013): 2490-2495.[8] Javey, Ali, et al. "High performance n-type carbon nanotube field-effect transistors with chemically doped contacts." Nano letters 5.2 (2005): 345-348.

Potassium (K) Doping, Introduce electron carriers

REMEDY FOR IMPERFECTION

1. Cleaning metallic CNTs[9]

G

D

S

G

D

SApply high voltage

Breakdown voltage of semiconductor CNT is larger than metallic CNT

[9] Kim, Sunkook, et al. "Current on/off ratio enhancement through the electrical burning process in ambient with/without oxygen for the generation of high-performance aligned single-walled carbon nanotube field effect transistors." Applied Physics Letters 97.17 (2010): 173102.

m-CNT s-CNT

REMEDY FOR IMPERFECTION

2. Mis-positioned CNT Immune Design[10]

[10] Zhang, Jie, et al. "Robust digital VLSI using carbon nanotubes." IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems 31.4 (2012): 453-471.

Etched Regions

Mis-positioned caused error After etch Mispositioned CNT-

immune

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