Verifying the physical role of upper-active-layer on charge transport together with bias stability in bilayer-channel oxide thin-film transistors

In this work, we report the fabrication of solution-processed bilayer-structure oxide thin-film transistors (TFTs) exhibiting superior electrical characteristics and enhanced positive/negative bias stabilities. This was achieved by tuning the carrier concentration and bandgap of the top active layer in the bilayer semiconductor. The characteristics of the top layer were modulated through aluminum (Al) doping in indium oxide semiconductors. Bilayer-channel TFTs with an optimized indium-aluminum-oxide top layer (In:Al ratio of 8:2) demonstrated effective electron transport via percolation conduction and exhibited high mobility. Furthermore, the optimized bilayer TFTs displayed small threshold voltage shifts under positive and negative bias stress, attributed to the effective formation of a quasi-two-dimensional electron gas and the suppression of oxygen vacancies. An in-depth study on engineering the carrier concentration and bandgap of the bilayer structure provides insights into material design and fabrication strategies for high-performance and stable heterostructure transistors.