All-Amorphous-Oxide Transparent, Flexible Thin-Film Transistors. Efficacy of Bilayer Gate Dielectrics

Abstract

Optically transparent and mechanically flexible thin-film transistors (TF-TFTs) composed exclusively of amorphous metal oxide films are fabricated on plastic substrates by combining an amorphous Ta₂O₅/SiO_<i>x</i> bilayer transparent oxide insulator (TOI) gate dielectric with an amorphous zinc−indium−tin oxide (a-ZITO) transparent oxide semiconductor (TOS) channel and a-ZITO transparent oxide conductor (TOC) electrodes. The bilayer gate dielectric is fabricated by the post-cross-linking of vapor-deposited hexachlorodisiloxane-derived films to form thin SiO_<i>x</i> layers (v-SiO_<i>x</i>) on amorphous Ta₂O₅ (a-Ta₂O₅) films grown by ion-assisted deposition at room temperature. The a-Ta₂O₅/v-SiO_<i>x</i> bilayer TOI dielectric integrates the large capacitance of the high dielectric constant a-Ta₂O₅ layer with the excellent dielectric/semiconductor interfacial compatibility of the v-SiO_<i>x</i> layer in a-ZITO TOS-based TF-TFTs. These all-amorphous-oxide TF-TFTs, having a channel length and width of 100 and 2000 μm, respectively, perform far better than a-Ta₂O₅-only devices and exhibit saturation-regime field-effect mobilities of ∼20 cm²/V·s, on-currents >10⁻⁴ A, and current on−off ratios >10⁵. These TFTs operate at low voltages (∼4.0 V) and exhibit good visible-region optical transparency and excellent mechanical flexibility.