Advantages of top-gate, high-k dielectric carbon nanotube field-effect transistors

The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized $900\mathrm{nm}$ $\mathrm{Si}{\mathrm{O}}_2$ as the gate insulator. This CNT FET was then covered with $\mathrm{Ti}{\mathrm{O}}_2$ to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized $\mathrm{Ti}{\mathrm{O}}_2$ ($\kappa \sim 80$ , equivalent oxide $\text{thickness}=0.25\mathrm{nm}$ ) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope $(67–70\mathrm{mV}∕\mathrm{dec})$ , highest transconductance $\left(1.3\mu \mathrm{S}\right)$ , and negligible hysteresis in terms of threshold voltage shift.