Carbon Nanotube Field Effect Transistors

CNTs are graphene nano thickness sheets rolled into tubes, considered as the fourth allotropic form of carbon, along with the original three, coal, graphite and diamond. They have unique electrical, mechanical, semiconducting properties and exist in two forms; single wall (SW) and wall in a wall structure, called as multiwall (MW), as shown in Figure 1 [19-21]. Sumio Iijima of Japan discovered multiwall (MW) CNT in 1991, followed by single wall CNT in 1993 along with Donald Bethune (independently) [19]. CNTs show both metallic and semiconducting properties (depending on their chirality or chirality vector), have length in few micrometer and diameter ranging from <1 nm to 50 nm. They are the best thermal conductors (better than diamond), have tensile strength 102 × more than that of steel, can have a current density of 103 × than Cu (109A/cm2). CNT based field effect transistor (CNTFET) is an important application of CNTs and the first CNTFET is fabricated by S. J. Trans et. al. [21], as shown in Figure 1. Because of the presence of CNT based channel in a CNTFET, it has a capability to outshine conventional MOSFET in future. The CV/I characteristics of a CNTFET is ~13× higher than that of a conventional n-MOSFET [20-25].