UBC Theses and Dissertations
High-frequency limits of carbon nanotube transistors Chen, Li
This thesis is focused on the high-frequency performance of carbon nanotube field-effect transistors (CNFETs). Such transistors show their promising performance in the nanoscale regime where quantum mechanics dominates. The short-circuit, common-source, unity-current-gain frequency ft is analyzed through regional signal-delay theory. An energy-dependent effective-mass feature has been added to an existing SP solver and used to compare with results from a constant-effective-mass SP solver. At high drain bias, where electron energies considerably higher than the edge of the first conduction sub-band may be encountered, ft for CNFETs is significantly reduced with respect to predictions using a constant effective mass. The opinion that the band-structure-determined velocity limits the high-frequency performance has been reinforced by performing simulations for p-i-n and n-i-n CNFETs. This necessitated incorporating band-to-band tunneling into the SP solver. Finally, to help put the results from different CNFETs into perspective, a meaningful comparison between CNFETs with doped-contacts and metallic contacts has been made. Band-to-band tunneling, which is a characteristic feature of p-i-n CNFETs, can also occur in n-i-n CNFETs, and it reduces the ft dramatically.
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