Annealing processes were investigated on Indium-Gallium-ZincOxide (IGZO) thin-film transistors (TFTs). Molybdenum and aluminum were used as contact metals which defined the working source/drain electrodes. Annealing was performed either pre-metal or post-metal deposition, in various gas ambients including air, oxygen, nitrogen, forming gas (5% H2 in N2) and vacuum. Premetal annealing in air ambient resulted in similar I-V characteristics on Mo-contact and Al-contact devices. A postmetal anneal for Mo-contact devices resulted in higher on-state current and steeper subthreshold slope, whereas the Al-contact devices experienced severe degradation suggesting the formation of an AlOx interface layer. A post-metal anneal at 400 °C in N2 followed by an air ambient ramp-down yielded Mo-contact devices with SS ~ 200 mV/dec, channel mobility µsat ~ 8.5 cm 2 /V•s, and improved stability over other anneal conditions.

Annealing processes were investigated on Indium-Gallium-Zinc-Oxide (IGZO) thin-film transistors (TFTs). Molybdenum and aluminum were used as contact metals which defined the working source/drain electrodes. Annealing was performed either pre-metal or post-metal deposition, in various gas ambient conditions including air, oxygen, nitrogen, forming gas (5% H2 in N2) and vacuum. Pre-metal annealing in air ambient resulted in similar I-V characteristics on Mo-contact and Al-contact devices. A post-metal anneal for Mo-contact devices resulted in higher on-state current and steeper subthreshold slope, whereas the Al-contact devices experienced severe degradation suggesting the formation of an AlOX interface layer. Oxidant exposure during anneal was vital for controlling the electronic properties of IGZO. A post-metal anneal at 400°C in N2 followed by an air ambient ramp-down yielded Mo-contact devices with channel mobility μsat ∼ 8.5 cm2/V·s and subthreshold swing SS ∼ 200 mV/dec. Electron-beam evaporated alumina was used for back-channel passivation which resulted in improved stability at the expense of slight degradation in device performance.

The influence of annealing ambient conditions and deposited passivation materials on indium-gallium-zinc-oxide (IGZO) thin-film transistor (TFT) performance is investigated. Results from annealing experiments confirm that a nominal exposure to oxidizing ambient conditions is required, which is a function of temperature, time and gas environment. Nitrogen anneal with a controlled air ramp-down provided the best performance devices with a mobility (µ sat ) of 11-13 cm 2 /V·s and subthreshold slope (SS) of 135-200 mV/dec, with some hysteresis. Plasma-deposited passivation materials including sputtered quartz and PECVD SiO 2 demonstrated a significant increase in material conductivity, which was not significantly reversible by an oxidizing ambient anneal. E-beam evaporated Al 2 O 3 passivated devices that were annealed in air at 400 °C demonstrated improved stability over time and suppressed hysteresis in comparison to unpassivated devices. Devices which were passivated with B-staged bisbenzocyclobutene-based (BCB) resins and annealed in air at 250 °C also exhibited suppressed hysteresis.

Flash-lamp annealing (FLA) has been investigated for crystallization of patterned amorphous silicon (a-Si) in the fabrication of NMOS and PMOS Thin-Film Transistors (TFTs) on display glass. Samples were exposed with a xenon flash irradiance of ∼30 kW/cm2 and pulse duration of 200 μs, with bolometer measurements showing an integrated energy of ∼6 J/cm2. Non-self-aligned TFTs fabricated from the resulting polycrystalline silicon demonstrated electron and hole channel mobility values in excess of 300 cm2/(Vs) and 100 cm2/(Vs), respectively. According to the authors’ knowledge, this is the first report of CMOS TFTs demonstrated using the FLA technique.

Capacitance-voltage (C-V) analysis is a valuable tool in separating the influence of material and interface defects from other factors that influence transistor operation. Thin-film transistors and interdigitated capacitors fabricated using sputtered IGZO have been studied to enhance the interpretation of defect states. Interdigitated capacitors are representative of the TFT channel region, and large-area designs provide a high capacitance swing from depletion to accumulation. Alumina was applied for back channel passivation, with annealing performed at 400 °C in oxidizing ambient conditions. Both I-V and C-V results were used with TCAD device simulation to develop a refined material and device model.