Rational Design of Different Ga Content Bilayer InGaZnO Thin-Film Transistors With Al₂O₃/HfO₂ Passivation Layer

This study investigated the effects of different Ga contents on the performance of single amorphous InGaZnO (a-IGZO) and bilayer InGa <tex-math notation="LaTeX">_(0.5% )</tex-math> ZnO/InGa <tex-math notation="LaTeX">_(1% )</tex-math> ZnO thin-film transistors (TFTs). Through rational design, a bilayer TFT exhibiting the best performance, including a <tex-math notation="LaTeX">Vₜₕ</tex-math> of 1.2 V, <tex-math notation="LaTeX">Iₒₙ</tex-math> / <tex-math notation="LaTeX">Ioff</tex-math> of 1 <tex-math notation="LaTeX">×</tex-math> 10 <tex-math notation="LaTeX">⁸</tex-math> , SS of 0.28 V/decade, and <tex-math notation="LaTeX">μ FE</tex-math> of 32.5 cm <tex-math notation="LaTeX">²</tex-math> /Vs, was obtained. This improved performance was attributed to the InGa <tex-math notation="LaTeX">_(0.5% )</tex-math> ZnO front layer enhancing the <tex-math notation="LaTeX">μ FE</tex-math> with low surface defect and high <tex-math notation="LaTeX">Nₑ</tex-math> and the InGa <tex-math notation="LaTeX">_(1% )</tex-math> ZnO back layer controlling the <tex-math notation="LaTeX">Vₜₕ</tex-math> with low <tex-math notation="LaTeX">VO</tex-math> and <tex-math notation="LaTeX">Nₑ</tex-math> in the bilayer device. Owing to the formation of energy band bending, the electrons transferred from the InGa <tex-math notation="LaTeX">_(0.5% )</tex-math> ZnO to InGa <tex-math notation="LaTeX">_(1% )</tex-math> ZnO layer. This resulted in the accumulation of free electrons near the interface, thereby enhancing the <tex-math notation="LaTeX">μ FE</tex-math> of the bilayer device. Moreover, a minor shift in the <tex-math notation="LaTeX">Vₜₕ</tex-math> (0.4 and <tex-math notation="LaTeX">$-$</tex-math> 0.5 V) of InGa <tex-math notation="LaTeX">_(0.5% )</tex-math> ZnO/InGa <tex-math notation="LaTeX">_(1% )</tex-math> ZnO TFTs with HfO <tex-math notation="LaTeX">₂</tex-math> /Al <tex-math notation="LaTeX">₂</tex-math> O <tex-math notation="LaTeX">₃</tex-math> dual passivation layer (PVL) was observed under positive and negative gate bias light illumination stress with relative humidity 60% condition. This was attributed to the HfO <tex-math notation="LaTeX">₂</tex-math> /Al <tex-math notation="LaTeX">₂</tex-math> O <tex-math notation="LaTeX">₃</tex-math> PVL protecting the channel from oxygen adsorption/desorption and environmental influences. Thus, the designed bilayer InGa <tex-math notation="LaTeX">_(0.5% )</tex-math> ZnO/InGa <tex-math notation="LaTeX">_(1% )</tex-math> ZnO TFTs with HfO <tex-math notation="LaTeX">₂</tex-math> /Al <tex-math notation="LaTeX">₂</tex-math> O <tex-math notation="LaTeX">₃</tex-math> PVL have enabled new pathways for achieving high-performance and highly stable oxide TFTs.