Oxide thin-film transistors (TFTs)
have attracted much attention
because they can be applied to flexible and large-scaled switching
devices. Especially, oxide semiconductors (OSs) have been developed
as active layers of TFTs. Among them, indium–gallium–zinc
oxide (IGZO) is actively used in the organic light-emitting diode
display field. However, despite their superior off-state properties,
IGZO TFTs are limited by low field-effect mobility, which critically
affects display resolution and power consumption. Herein, we determine
new working mechanisms in dual-stacked OS, and based on this, we develop
a dual-stacked OS-based TFT with improved performance: high field-effect
mobility (∼80 cm2/V·s), ideal threshold voltage
near 0 V, high on–off current ratio (>109), and
good stability at bias stress. Induced areas are formed at the interface
by the band offset: band offset-induced area (BOIA) and BOIA-induced
area (BIA). They connect the gate bias-induced area (GBIA) and electrode
bias-induced area (EBIA), resulting in high current flow. Equivalent
circuit modeling and the transmission line method are also introduced
for more precise verification. By verifying current change with gate
voltage in the single OS layer, the current flowing direction in the
dual-stacked OS is calculated and estimated. This is powerful evidence
to understand the conduction mechanism in a dual-stacked OS-based
TFT, and it will provide new design rules for high-performance OS-based
TFTs.