Nanotech 2010

Aligned Carbon Nanotubes for Beyond-CMOS Electronics

C. Wang, K. Ryu, A. Badmaev, C. Zhou
University of Southern California, US

Keywords: aligend nanotubes, high density, field-effect transistors, CMOS


Aligned carbon naotubes are very desirable for carbon based electronic devices and integrated circuits owing to their advantages of registration-free fabrication, high device yield, and small device-to-device variation. For the aligned nanotubes, one of the most important technology components is to increase the nanotube density. High density aligned nanotubes can be extremely helpful to improve the current driving capability, transconductance, and cut-off frequency of the devices. Here in this talk, we report low-pressure chemical vapor deposition (LPCVD) ethanol synthesis of high density aligned nanotubes with density as high as 30 tubes/µm. Then a facile stacking multiple transfer technique was used to further increase the nanotube density to > 55 tubes/µm. Furthermore, high-performance back-gated carbon nanotube field-effect transistors were fabricated on these ultra high density aligned nanotubes and the devices exhibit on-current density of 92.4 µA/µm, normalized transconductance of 13.3 µS/µm, and intrinsic nanotube mobility of ~ 12,000 cm2/Vs. Another important technology component for integrated circuit application is to achieve air-stable n-type transistors from carbon nanotubes. We demonstrate that by using metal contacts with small work function such as Gadolinium (Gd), the transistors exhibit predominantly n-type behavior since the Fermi level of the metal is aligned with the conduction band of the carbon nanotubes. In order to achieve air stable operation, E-beam evaporated SiO2 was used for passivation and the devices exhibit clear n-type characteristics when measured in air. Further more, stepper and E-beam lithography were used to pattern both p-type (Pd contact) and n-type (Gd contact) devices on the same nanotubes and an integrated air-stable CMOS inverter with a gain of 3.6 was demonstrated. Rectifying diodes with Pd contact for p-side and Gd contact for n-side was also demonstrated.
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