Moore's Law: Si CMOS Technology

1. INTRODUCTION

1.1 Moore’s Law
Moore’s law in 1975 suggests that the component density in any integrated circuit approximately doubles every 2 years. The growing trends in CMOS technology does give us a perpetual reminder of the Moore’s law. Moore’s law has been kept unabated because of the sole reason that Si CMOS technology was scalable. Scalability has given solid state devices the boon to consume less power and occupy a smaller area while still being cheap. However the scaling down has led to dominating effects that are unavoidable. This has led to investments in viable alternate technologies to replace the Si CMOS at feature sizes less that 25nm(?). Research has been undertaken to utilize Carbon as a replacement to Silicon because of

[5] length of 40nm. [5]

1.4 Carbon and Carbon Nanotubes.
Carbon purely occurs as 8 allotropes namely Graphite, Diamond, Lonsdaleite, C60(Buckminsterfullerene), C540, C70, Amorphous carbon and single walled carbon nanotube.[2] The electronics is mainly interested in two of it, Graphite and Carbon nanotube.
Graphite occurs as layered planar structures and each layer carbon atoms are arranged in a hexagonal lattices.
Single walled carbon nanotube is obtained on rolling up a single sheet of graphite called the graphene. CNTs are cylindrically arranged carbon molecules which have exceptional physical and thermal capabilities. The electrical properties of the Carbon nanotube is determined based on the type of rolling, the diameter and a few other factors. The two predominant type of rolled structures of a nanotubes are Zig-Zag and Arm Chair.

Fig 4: Physical structure of CNFET- Armchair and

Nanotubes where the value of is an integral multiple of 3 exhibit metallic behavior while the rest exhibit semiconducting behavior. The energy band structure of a CNT enables it to achieve ballistic transport at relatively larger channel lengths. Ballistic transport mechanism is achieved when an electron travels from the source to drain without undergoing collision anywhere in the channel. A transistor is said to be ballistic if the channel length is smaller than the mean free path of the electron. Mean free path is defined as the distance the electron travels before it undergoes collision. Since there is barely any collision in the transport from Source to Drain the energy loss is minimal. The band gap of a semiconducting CNT is inversely proportional to its diameter. Bandgap of a semiconductor is defined as the energy require to break a covalent bond to release an electron for