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

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 (
${V}_{TG}$
)-swept threshold voltage (
${V}_{T,TG}$
) with back-gate voltage (
${V}_{BG}$
) is essential. In this work, the influence of positive bias stress (PBS) condition on both
$\beta = \partial {V}_{T,TG}/\partial {V}_{BG}$
and
$\Delta \beta = \partial \Delta {V}_{T,TG}/\partial {V}_{BG}$
is investigated in DG a-IGZO TFTs, using the subgap density-of-states (DOS) extracted before and after PBS. While
$\Delta \beta $
remains almost constant in the PBS condition of
${V}_{TG}/{V}_{BG}=30$
/-30 V, the
${V}_{TG}={V}_{BG}=30$
V condition shows the complicated nonlinear relationship between
$\Delta {V}_{T,TG}$
and
${V}_{BG}$
. It is found that
$\lambda = \delta \Delta \beta /\delta {V}_{BG}$
, as the parametric indicator describing the PBS-induced degradation of linearity for the
${V}_{BG}$
-controlled
${V}_{T,TG}$
, is
$\times 7$
larger (less linear) at
${V}_{TG}={V}_{BG}=30$
V than at
${V}_{TG}/{V}_{BG}=30$
/−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
${V}_{TG}/{V}_{BG}=30$
/−30 V is a more advantageous condition in the viewpoint of the
$\Delta {V}_{T,TG}$
linear with
${V}_{BG}$
, in comparison with
${V}_{TG}={V}_{BG}=30$
V.