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We report the design and fabrication of a high-yield, a high-speed, and an ultranarrow gate driver with amorphous-indium - gallium - zinc-oxide thin-film transistors (TFTs). A single stage of the gate driver consists of nine TFTs and one capacitor. For supply voltage (VDD) of 20 V, the gate driver operates with a pulsewidth of 2 μs, which is compatible with a 4k2k display operated at 240 Hz. In addition, the proposed gate driver is ultrasmall in physical size, which is only 30 μm in width (pitch) and 720 μm in length, and thus suitable for small-size, high-resolution, and narrow bezel display. [ABSTRACT FROM AUTHOR]

We report the achievement of flexible oxide thin-film transistors (TFTs) that are highly robust under mechanical bending stress. Fabricated on solution-processed polyimide, the oxide TFTs employ the dual-gate structure with an amorphous-indium-gallium-zinc oxide (a-IGZO) semiconductor, silicon dioxide gate insulators, and molybdenum gate and source/drain electrodes. High mechanical stability is achieved by shorting the two gates together to induce bulk accumulation (BA)—a condition in which the channel accumulation layer of electrons extends the entire depth of the active layer. It is shown experimentally that the BA a-IGZO TFTs exhibit better stability under bending stress compared with single gate-driven TFTs. From TCAD simulations, the immunity to slight variations in carrier concentration under tensile strain is found to be a result of the high gate-drive intrinsic of the BA TFTs. [ABSTRACT FROM AUTHOR]

The effect of bulk accumulation on switching speed of dual-gate amorphous indium–gallium–zinc-oxide thin-film transistor (TFT)-based circuits is investigated. Given that bulk accumulation is achieved by synchronized driving of the top gate (TG) and bottom gate, it can be modulated by varying the length of the TG ( \textrm L{{\textrm {TG}}} ) for fixed source–drain distance ( $L$ ). It is confirmed from fabricated ring oscillators that switching speed increases with increasing \textrm L{{\textrm {TG}}} for fixed $L$ , verifying that bulk accumulation improves switching speed. However, switching speed drops dramatically when the TG overlaps the source/drain electrodes due to additional parasitic capacitance. TFT-circuits with the longest, but nonoverlapping TGs are demonstrated to exhibit the fastest switching speed; operation frequency exceeding 2.63 MHz for input voltage \textrm {V}_{{{\textrm {DD}}}} of 20 V, which is also the fastest among all inverted staggered amorphous-oxide-semiconductor TFT-based circuits. [ABSTRACT FROM AUTHOR]

We report an abnormal negative threshold-voltage shift $(\Delta V_{{\rm TH}}) in bulk-accumulation (dual-gate driven) amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) after application of positive-bias-stress (PBS). In devices annealed at 250 ^\circC for 2 h in vacuum, the negative \Delta VTH is accompanied with subthreshold swing degradation, consistent with PBS-induced defect creation. Negative-bias-stress induces negligible $\Delta V_{{\rm TH}}$ , ruling out ion migration in the gate-insulator. By varying the top-gate length, it is found that the negligible $\Delta V_{{\rm TH}} is a function of bulk-accumulation. However, after vacuum annealing at 250 ^\circC for 100 h, PBS induces negligible \Delta VTH , verifying that the negative $\Delta V_{{\rm TH}}$ in short-time annealed devices is related to defects in the bulk a-IGZO. Therefore, good PBS stability can be achieved in bulk-accumulation dual-gate a-IGZO TFTs by long-time vacuum anneal. [ABSTRACT FROM AUTHOR]