High-performance amorphous indium-gallium-zinc-oxide thin-film-transistor and its applications

• Main Author: Li, Yuanbo
• Other Authors: Chen Tupei
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Electrical and electronic engineering
• Online Access: https://hdl.handle.net/10356/164692
• Institution: Nanyang Technological University

Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistor (TFT) is an emerging electronic device with many applications, such as active-matrix high-resolution display, wearable electronics, embedded memories, synaptic devices, sensors, etc. The broad spectrum of applications of the IGZO TFT is attributed to the TFT’s large carrier mobility, low leakage current, high transparency, good uniformity, low-temperature, low-complexity, and low-cost fabrication process, as well as the compatibility with various dielectric materials. Nevertheless, there still exist some challenges for IGZO TFT such as the limited driving current for ultrahigh definition display and poor reliability under external stress. In this thesis, the author was dedicated to improving the performance of the IGZO TFT through various techniques. Applications based on high-performance IGZO TFTs were explored and demonstrated as well. IGZO TFTs were fabricated with the staggered bottom-gate structure thanks to its simple fabrication process. From the top to the bottom, novel source/drain contacts engineering, room-temperature passivation technology, and novel ion-conductive gate-dielectric adoption were applied on the transparent IGZO TFTs respectively for the improvements of IGZO TFT performance and realization of advanced applications. In the end, an 8×8 1T1R array was fabricated based on the integration of high-performance IGZO TFTs and HfO2-based resistive memory (ReRAM), which is promising in applications for embedded memory technology. Specifically, 1) by virtue of the good contact between Ti and IGZO, a transparent IGZO TFT with an ultrathin Ti layer as the source/drain contacts was demonstrated. The insertion of a 10 nm Ti layer between ITO and IGZO successfully improved the carrier mobility of the TFT by three folds and reduced the contact resistance of the TFT by over three folds, with the optical transmittance of the whole device maintained at a high level. 2) a layer of 20 nm sputtered AlOx was capping on the transparent IGZO TFT as a passivation layer, which aimed to provide protection to the IGZO layer from the penetration of ambient molecules. At the same time, the deposition of the AlOx layer induced an interfacial In-rich layer at the AlOx/IGZO interface, which increased the carrier concentration in the IGZO layer. As a result, the mobility of the TFT was largely improved from 6.292 cm2/Vs to 69.01 cm2/Vs. This tremendous enhancement of the carrier mobility increased the driving current of the IGZO TFT by one order as well. 3) by changing the dielectric material from Al2O3 to the ion-conductive TaOx, a transparent synaptic IGZO TFT was achieved under stimulation of either electronic pulses or photoelectric pulses. Under various stimulations, behaviors of drain current of the TFT can well emulate the excitatory post-synaptic current, short-term memory plasticity, short-term memory transition to long-term memory, and long-term potentiation/depression. Particularly, long-term potentiation/depression with large Gmax/Gmin and small nonlinearity was achieved. 4) the high-performance IGZO TFTs were integrated with HfO2-based ReRAM. The TFT with Ti/Au/Ti/Pt multi-stack source/drain contacts showed large driving current and good reliability under self-heating stress. On the other hand, the ReRAM with an ultrathin tunnelling layer inserted between the top electrode and the HfO2 switching layer showed largely reduced device-to-device and cycle-to-cycle variations in memory parameters under a small compliance current (0.5 mA).