Carbon nanotube field effect transistors for power application

Abstract

Carbon nanotubes (CNTs) are nanometer-diameter cylinders formed from rolled-up graphene sheets which have found widespread interests due to their many excellent electrical properties. In particular, most of them are direct bandgap semiconductors from which carbon nanotube field effect transistors (CNTFETs) can be made. The small feature size and high electron mobility of the CNT makes it attractive and a good candidate to replace modern MOSFETs. So far, most fabricated CNTFETs conduct currents only on the order of microamps under low voltage bias which cannot be used to drive large output loads. In this work, we attempt to explore the ultimate performance benefits from utilizing multiple CNTs for CNTFETs. Two ways of making multi-tube CNTFETs are demonstrated in this thesis. Devices are fabricated, measured and analyzed. A simple model is used to evaluate the ideal ballistic behavior of CNTFETs. Parasitics that are measured from experiments and extracted from numerical tools are added to the model. As an application, we compare the performance of CNTFETs with MOSFETs, both used as power transistors in a Buck DC-DC converter circuit.