Electrical Characteristics of Ultrathin InZnO Thin-Film Transistors Prepared by Atomic Layer Deposition

Abstract

In this article, enhancement-mode thin-film transistors (TFTs) with atomic layer deposition (ALD)-derived ultrathin (≈3 nm) amorphous indium–zinc oxide (a-IZO) channel were demonstrated. Our devices showed improved device characteristics as benchmarked with thicker IZO thin-film channels. The ALD-deposited IZO channel TFT with an In/Zn ratio of ≈6:4 exhibited a high field-effect channel mobility ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu _{\text {FE}}{)}$ </tex-math></inline-formula> of 53.6 cm2/V-s, 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">${V}_{\text {th}}{)}$ </tex-math></inline-formula> of 0.28 V, a low subthreshold gate swing of 74 mV/decade, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{ \mathrm{\scriptscriptstyle ON}}/I_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio of > <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{9}}$ </tex-math></inline-formula> , and a contact resistance of 0.18 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> after 300°C anneal in oxygen atmosphere. Physical analysis, including X-ray and ultraviolet (UV) photoelectron spectra of IZO films, was conducted to understand the mechanisms of enhancement in electrical performance after annealing. The threshold voltages of the TFT also exhibited high stability ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\text {th, PBS}} &lt; 16$ </tex-math></inline-formula> mV and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{\text {th, NBS}} &lt; 12$ </tex-math></inline-formula> mV) after positive bias stress (PBS) and negative bias stress (NBS) test for 3600 s. To the best of our knowledge, we reported the TFT with thinnest IZO ternary oxide semiconductor (OS) channel exhibiting superior channel mobility and subthreshold characteristics.