Self-Aligned Coplanar a-IGZO TFTs and Application to High-Speed Circuits

Abstract

We report a self-aligned coplanar amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) using an a-IGZO/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> stack layer. From the channel-length dependence of the total resistance for the TFTs, the channel and parasitic resistances were found to be 8.4 kΩ/μm and 9.7 kΩ/sq, respectively. The fabricated a-IGZO TFT exhibits field-effect mobility of 23.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V ·s, threshold voltage of 3.6 V, and gate voltage swing of 203 mV/dec. A 23-stage ring oscillator made of the self-aligned TFTs exhibits a propagation delay time of 17 ns/stage at a supply voltage of 22 V.