Advanced Soft Electronics Laboratory (ASEL)

This study investigates the impact of source/drain materials on channel shortening in back-channel-etched (BCE) oxide thin-film transistors (TFTs) employing an indium-tin-based oxide semiconductor. Molybdenum (Mo) and Molybdenum-aluminum-titanium (MoAlTi) electrodes are systematically compared to evaluate their effects on channel shortening and device performance. Combined electrical characterization and materials analyses indicate that MoAlTi electrodes induce stronger contact-related interfacial effects, resulting in more pronounced effective channel length reduction and consequent overestimation of field-effect mobility. Temperature-dependent TLM analysis suggests that thermally activated defect-mediated processes are involved in the observed channel shortening behavior, although the diffusing species cannot be uniquely identified from the activation energy alone. TEM and XPS analyses further support stronger interfacial oxidation and oxygen-vacancy-related bonding changes in the MoAlTi contact system compared to the Mo contact system. These findings underscore the necessity of accounting for effective channel length reduction in mobility extraction and highlight the critical role of electrode/oxide interfacial reactions in scaled oxide TFTs.

We report an IZO bilayer channel architecture for high-performance oxide thin-film transistors (TFTs), where the thickness of the ultrathin sputtered IZO layer on the solution-processed IZO is utilized to control film morphology, carrier transport, and turn-on voltage behavior. A solution-processed IZO bottom layer was fixed at approximately 10 nm, followed by the sputtered IZO overlayer, which was systematically varied from 3 to 5 nm. The addition of the ultrathin sputtered IZO layer significantly improved the electrical properties of the solution-processed IZO TFTs by modulating film morphology and carrier transport behavior. Power-law mobility analysis revealed that the 3 nm bilayer device remains governed by trap-limited conduction, whereas the 4 and 5 nm bilayer devices undergo a gate-field-induced transition from trap-limited conduction to percolation conduction. This transition is attributed to the formation of an interface-assisted percolation pathway around the buried solution IZO/sputtered IZO interface. An optimized 4 nm sputtered IZO overlayer provides the best-balanced performance, including near-zero turn-on voltage, improved switching behavior, mobility enhancement, and gate-voltage controllability, which offers a practical route for high-performance solution-processed oxide TFTs.

A precise strategy to control hydrogen incorporation is essential for achieving high-performance oxide thin-film transistors (TFTs) as hydrogen plays a key role in tuning carrier concentration and passivating defect states. In this study, we report a top-gate oxide thin-film transistor structure that utilizes a plasma-enhanced atomic layer deposition (PEALD) supercycled SiO2–Al2O3 gate insulator (GI), enabling precise hydrogen control through a tunable layering sequence. Hydrogen incorporation into the active channel is modulated with precise control by varying the number of hydrogen-rich SiO2 subcycles. Comprehensive analyses reveal that moderate hydrogen incorporation effectively passivates oxygen-related defects while introducing shallow donor states, enhancing mobility, and suppressing charge trapping. The optimized device with ten cycles of H-rich SiO2 exhibits a high field-effect mobility of 47.4 cm2/V·s, a turn-on voltage (Von) of −0.46 V, a subthreshold swing of 71.3 mV/dec and negligible hysteresis, an on/off current ratio of ∼107, and superior bias stability under positive and negative stress conditions. In contrast, excess hydrogen from 15 cycles leads to the loss of switching behavior caused by the intermixing of GI layers, resulting in uncontrolled hydrogen diffusion and excessive carrier generation. These results demonstrate that the PEALD supercycle process offers a reliable strategy for hydrogen modulation in oxide semiconductors, enabling an optimized trade-off between mobility and stability in high-performance TFTs.