Effect of Positive Bias Stress on the Back-Gate Voltage-Modulated Threshold Voltage in Double-Gate Amorphous InGaZnO Thin-Film Transistors

Abstract

In the back-end-of-line double-gate (DG) amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs), the linearity of top-gate voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}$ </tex-math></inline-formula> )-swept 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">${V}_{T,TG}$ </tex-math></inline-formula> ) with back-gate voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{BG}$ </tex-math></inline-formula> ) is essential. In this work, the influence of positive bias stress (PBS) condition on both <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta = \partial {V}_{T,TG}/\partial {V}_{BG}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \beta = \partial \Delta {V}_{T,TG}/\partial {V}_{BG}$ </tex-math></inline-formula> is investigated in DG a-IGZO TFTs, using the subgap density-of-states (DOS) extracted before and after PBS. While <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \beta $ </tex-math></inline-formula> remains almost constant in the PBS condition of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}/{V}_{BG}=30$ </tex-math></inline-formula> /-30 V, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}={V}_{BG}=30$ </tex-math></inline-formula> V condition shows the complicated nonlinear relationship between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{T,TG}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{BG}$ </tex-math></inline-formula> . It is found that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda = \delta \Delta \beta /\delta {V}_{BG}$ </tex-math></inline-formula> , as the parametric indicator describing the PBS-induced degradation of linearity for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{BG}$ </tex-math></inline-formula> -controlled <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{T,TG}$ </tex-math></inline-formula> , is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 7$ </tex-math></inline-formula> larger (less linear) at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}={V}_{BG}=30$ </tex-math></inline-formula> V than at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}/{V}_{BG}=30$ </tex-math></inline-formula> /−30 V. The origin of this non-linearity is comprehensively explained based on the model of the excessive oxygen-related defect creation resulting from broken peroxy linkage. Our result suggests that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}/{V}_{BG}=30$ </tex-math></inline-formula> /−30 V is a more advantageous condition in the viewpoint of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {V}_{T,TG}$ </tex-math></inline-formula> linear with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{BG}$ </tex-math></inline-formula> , in comparison with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{TG}={V}_{BG}=30$ </tex-math></inline-formula> V.