Temperature Gradient ZnO Deposited via ALD for High-Performance Transistor Applications
Bowen Che, Hao Zhang, Jun Yang, Jie Qi, Xingwei Ding, Jianhua Zhang
Abstract
This work reports an alternative atomic layer deposition (ALD) method to fabricate ZnO thin-film transistors (TFTs). The ZnO film is deposited with temperature naturally-cooling process from 200 to 100°C, called a “temperature gradient ZnO (TG-ZnO)”). After optimized annealing treatment at 300°C, the TG-ZnO TFT shows an excellent performance compared to those fabricated with traditional constant temperature deposition, including a high saturation mobility <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\left(\mu_{\text {sat }}\right)$ </tex-math></inline-formula> of 11.8 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Vs, which is 5 times higher than the ZnO TFT, a good on/off-state current ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\left(I_{\mathrm{on}} / I_{\mathrm{off}}\right)$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.9 \times 10^{7}$ </tex-math></inline-formula> , a small subthreshold swing ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$SS$ </tex-math></inline-formula> ) of 175 mV/decade and a threshold voltage <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\left(V_{\mathrm{th}}\right)$ </tex-math></inline-formula> of 1.1 V. Meanwhile, the TG-ZnO TFT has better crystallization than 100°C-ZnO and lower oxygen vacancies than 200°C-ZnO. These characters enable the TG-ZnO TFT not only to maintain a high mobility, but also to present a satisfactory <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm{on}} / I_{\mathrm{off}}$ </tex-math></inline-formula> ratio. This promising deposition technique provides a new idea for fabricating TFTs with high mobility.