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

• Published in: IEEE transactions on electron devices 2018-09, Vol.65 (9), p.3796-3802
• Main Authors: Petti, Luisa, Greco, Emanuel, Cantarella, Giuseppe, Munzenrieder, Niko, Vogt, Christian, Troster, Gerhard
• Format: Article
• Language: English
• Subjects: Fabrication; Flexible electronics; indium–gallium–zinc oxide (IGZO); Lasers; Lithography; Logic gates; mechanical strain; Resists; Substrates; Thin film transistors; thin-film transistor (TFT); transit frequency
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2018.2851926

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.