Ultra-Low Temperature Ozone Annealing for Decreasing Sub-Threshold Swing of Oxide Thin Film Transistors

Abstract

Indium gallium zinc oxide thin film transistor (IGZO-TFT) with low sub-threshold swing (SS) is realized by ozone (O3) annealing. The O3-annealed temperature is varied to systematically investigate its impact on electrical properties of IGZO thin films and IGZO-TFT compared with as-deposited IGZO thin films and devices. The experimental findings demonstrate a reduction in the relative concentration of oxygen vacancies in IGZO thin films compared to their as-deposited counterparts. Meanwhile, the density of the interface trap state (Nt) is decreased and shows an inverse correlation with increasing O3-annealed temperature. When the IGZO-TFT O3-annealed at 75 ℃, it exhibits satisfactory electrical properties, with a sub-threshold swing (SS) decreased into 140 mV/decade, a saturation mobility (µsat) is maintained at 4.2 cm2/V·s, a threshold voltage (Vth) of 0.7 V and an Ion/Ioffof 8.6 × 108. Finally, the high-power impulse magnetron sputtering (HiPIMS) IGZO-TFT through ultra-low temperature ozone annealing at 75 ℃ for only 180 s, exhibits a low subthreshold swing (SS). This study provides favorable conditions for the application of IGZO-TFT that demand ultra-fast response, especially under low-temperature conditions.

Keywords: ozone annealing, low SS, oxide TFT, ultra-low temperature