Optimization of Atomic-Layer-Deposited Zinc–Tin-Oxide Thin-Film Transistors via Controlled Aluminum Doping

High Resolution Image Download MS PowerPoint Slide This study investigated the physical and electrical properties of atomic-layer-deposited amorphous aluminum-doped zinc–tin-oxide ( a -AZTO) thin films and thin-film transistors (TFTs) using the a -AZTO channel. Al doping levels were controlled by adjusting the Al 2 O 3 subcycle within the a -AZTO supercycle. The as-deposited a -AZTO films exhibited layered structures consisting of an a -ZTO matrix and amorphous Al 2 O 3 layers, some of which substituted Zn atoms within the a -ZTO layer. As the number of Al 2 O 3 layers increased, the band gap energy and crystallization temperature of the a -AZTO films increased from 3.37 eV and 670 °C (undoped) to 3.56 eV and 740 °C (18% Al cationic fraction), respectively. The optimized a -AZTO ( a -A3ZTO, 6.5% Al cationic fraction) TFT, incorporating a 10-nm-thick HfO 2 /30-nm-thick SiO 2 stacked gate insulator, exhibited a subthreshold swing of 81 mV/decade, a threshold voltage of −0.30 V, and a saturation mobility of 6.07 cm 2 /(V s). Additionally, the a -A3ZTO TFT showed a lower contact resistance (11.7 kΩ) with TiN source/drain electrodes compared to the undoped a -ZTO TFT (12.1 kΩ). Moreover, the a -A3ZTO TFT demonstrated improved bias stress stability compared to the undoped a -ZTO TFT, with threshold voltage shifts of −0.20 and 0.60 V under negative bias stress and positive bias stress, respectively, after a stress time of 1000 s. This enhanced stability is attributed to the decreased oxygen vacancy concentration in the a -A3ZTO channel and the presence of a thin Al 2 O 3 layer at the channel’s back surface.