Structural advantages of rectangular-like channel cross-section on electrical characteristics of silicon nanowire field-effect transistors

We have experimentally demonstrated structural advantages due to rounded corners of rectangular-like cross-section of silicon nanowire (SiNW) field-effect transistors (FETs) on on-current (ION), inversion charge density normalized by a peripheral length of channel cross-section (Qinv) and effective carrier mobility (μeff). The ION was evaluated at the overdrive voltage (VOV) of 1.0 V, which is the difference between gate voltage (Vg) and the threshold voltage (Vth), and at the drain voltage of 1.0 V. The SiNW nFETs have revealed high ION of 1600 μA/μm of the channel width (wNW) of 19 nm and height (hNW) of 12 nm with the gate length (Lg) of 65 nm. We have separated the amount of on-current per wire at VOV = 1.0 V to a corner component and a flat surface component, and the contribution of the corners was nearly 60% of the total ION of the SiNW nFET with Lg of 65 nm. Higher Qinv at VOV = 1.0 V evaluated by advanced split-CV method was obtained with narrower SiNW FET, and it has been revealed the amount of inversion charge near corners occupied 50% of all the amount of inversion charge of the SiNW FET (wNW = 19 nm and hNW = 12 nm). We also obtained high μeff of the SiNW FETs compared with that of SOI planar nFETs. The μeff at the corners of SiNW FET has been calculated with the separated amount of inversion charge and drain conductance. Higher μeff around corners is obtained than the original μeff of the SiNW nFETs. The higher μeff and the large fractions of ION and Qinv around the corners indicate that the rounded corners of rectangular-like cross-sections play important roles on the enhancement of the electrical performance of the SiNW nFETs.

Research highlights
► Silicon nanowire n-type field-effect transistors with an on-current of 1600 μA/μm.
► Structural advantages of the rectangular-like cross-section.
► Contributions of corners were nearly 60% of the on-current.
► An increase of an inversion carrier density and the effective carrier mobility around corners.
► The on-current is influenced by the cross-sectional shapes.