Regional signal-delay analysis applied to high-frequency carbon nanotube FETs

A regional signal-delay analysis is presented for field-effect transistors intended for operation at very high frequencies. For the example used here of a doped-contact carbon nanotube field-effect transistor, the analysis reveals that tunneling into the channel region of the device, and modulation of the space-charge regions in the source and drain adjacent to the channel, are the principal contributors to the overall delay. A recently proposed lower limit to the signal delay time in the channel is critically examined via the introduction of a local signal velocity.