**1. Introduction**

40 VLSI Design

Xu, G. (2006). Thermal nodeling of multi-core processors, *Proceedings of 10th IEEE Intersociety* 

*Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITHERM)*, ISBN: 0-7803-9524-7, San Diego, CA., USA., May 2006, pp. 96-100.

> With the reduction in power consumption and size chip, the electronic industry has been searching novel strategies to overcome these constraints with an optimal performance. Carbon nanotubes (CNTs) due to their extremely desirable electrical and thermal properties have been considered for their applicability in VLSI Design. CNTs are defined as sheets of graphene rolled up as hollow cylinders. They can basically be classified into two groups: single-walled (SWNTs) and multi-walled (MWNTs) as shown in Figure 1. SWNTs have one shell or wall and whose diameter ranging from 0.4 to 4 nm, while MWNTs contain several concentric shells and their diameter ranging from several nanometers to tens of nanometers.

Fig. 1. Types of carbon nanotubes: single-walled nanotube (SWNT) and multiple-walled nanotube (MWNT).

The electrical properties the SWNTs can be either of metallic or semiconducting materials depending on their chirality, that is, the direction in which they get rolled up. However, MWNTs are always metallic materials. The main applications of carbon nanotubes in

Carbon Nanotube- and Graphene Based Devices, Circuits and Sensors for VLSI Design 43

effects in carbon nanotubes with small diameter, which can influence in the electrical properties. A metallic carbon nanotube can present semiconducting behavior and vice versa

Fig. 2. Classification of carbon nanotubes by chiral indices: zig-zag, chiral, and armchair.

Fig. 3. Classification of carbon nanotubes by electrical properties: (a) metallic nanotube, (b)

The interaction among electrons in an one-dimensional conductor such as a carbon nanotube can be modeled as a Tomonaga-Luttinger liquid, since electronic properties are derived of the collective excitations of charge and spin waves with a bosonic nature, that is, mass-less current flow (Danilchenko et al., 2010). Carbon nanotubes show two different electrical behaviors depending of the range of temperature: ballistic current transport at room temperature and Coulomb blockade phenomena at low temperatures. Ballistic transport is presented when the effective distance between contacts, where voltage is applied, is shorter than the mean free path. Coulomb blockade occurs when electrons hop on to and off from a single atom between two contacts due to a high contact electrical

semiconducting nanotube, and (c) moderate semiconducting nanotube.

resistance (Hierold, 2008; Léonard, 2009).

(Avouris, 2002).

electronics are biochemical sensors, data storage, RF applications, logic circuits and/or semiconductor materials (Xu et al., 2008). Nowadays, graphene nanoribbons (GNRs) or carbon nanotubes unrolled are presented as attractive candidate for next-generation of integrated circuit applications derived of the anomalous quantum Hall effects and massless Dirac electronic behavior (Lu & Lieber, 2007).

The main objective of this review related with carbon nanotubes and graphene nanoribbons is assessing the current status in VLSI design and provides a vision of the future requirements for electrical subsystems based on carbon nanotubes: technology, products and applications. This chapter presents a comprehensive study of the applicability of carbon nanotubes and graphene nanoribbons as base materials, with special emphasis into the advantages and limitations, in the design of elements for VLSI design such as interconnects, electronic devices such field-effect transistors, diodes and supercapacitors; optoelectronic devices such as solar cells and organic light-emitting diodes; electronic circuits such as logic gates, and digital modulators; and bio/chemical sensors such as biosensors and gas sensors.
