Carbon nanotube transistors and logic circuits

We discuss our recent efforts to develop high performance carbon nanotube field effect transistors (CNTFETs) and logic circuits. By improving the metal nanotube contacts the characteristics of the CNTFETs are greatly enhanced. Analysis shows that the performance of p-type CNTFETs is already competitive to that of silicon p-MOSFETs. In addition to the p-CNTFETs, we present techniques by which ambipolar and pure n-type CNTFETs can be fabricated. A particularly simple process involving the annealing in vacuum of a p-CNTFET is shown to convert it to an nCNTFET. This conversion is reversible, and re-exposure to oxygen leads to a p-CNTFET. Evidence is found that the key effect of oxygen involves modification of the contact barriers. Having complementary CNTFETs (i.e. p- and n-type) allows us to build the first integrated circuits. We present results on a NOT logic gate. Both an inter-molecular gate involving two separate CNTFETs, and an intra-molecular gate where the logic function is encoded along the length of a single tube are demonstrated. (C) 2002 Elsevier Science B.V. All rights reserved.