Comparison of the device structures (cross-sectional view) and fabrication processes between (a) 3-D nano trench Si NM flexible RF TFTs and (b) conventional 2-D TFTs. The effective channel lengths Lch are marked in red in (a3,b3). The smallest Lch of the nano trench TFT can reach down to 50 nm via NIL and that of the conventional TFT can only reach down to about 1.5 μm. (a1) Blanket phosphorous ion implantation and thermal anneal. (a2) Nano trench formation via nanoimprint. (a3) Final structure of nano trench TFT where the channel length Lch is defined by nanoimprint. (b1) Photolithography to define S/D regions for ion implantation. (b2) Selective ion implantation and thermal anneal. (b3) Final structure of conventional TFT where the channel length Lch is limited by gate electrode and dopant out-diffusion during ion implantation and thermal anneal.