Flexible In–Ga–Zn–O Thin-Film Transistors With Sub-300-nm Channel Lengths Defined by Two-Photon Direct Laser Writing

Abstract

In this paper, the low-temperature (≤150 °C) fabrication and characterization of flexible indium–gallium–zinc–oxide (IGZO) top-gate thin-film transistors (TFTs) with channel lengths down to 280 nm is presented. Such extremely short channel lengths in flexible IGZO TFTs were realized with a novel manufacturing process combining two-photon direct laser writing (DLW) photolithography with Ti/Au/Ti source/drain e-beam evaporation and liftoff. The resulting flexible IGZO TFTs exhibit a saturation field-effect mobility of 1.1 cm $^{\textsf {2}}\cdot \textsf {V}^{-\textsf {1}}\cdot \text {s}^{-\textsf {1}}$ and a threshold voltage of 3 V. Thanks to the short channel lengths (280 nm) and the small gate to source/drain overlap ( $5.2~\mu \text{m}$ ), the TFTs yield a transit frequency of 80 MHz (at 8.5-V gate–source voltage) extracted from the measured S-parameters. Furthermore, the devices are fully functional when wrapped around a cylindrical rod with 6-mm radius, corresponding to 0.4% tensile strain in the TFT channel. These results demonstrate a new methodology to realize entirely flexible nanostructures and prove its suitability for the fabrication of short-channel transistors on polymer substrates for future wearable communication electronics.