Engineering a Subnanometer Interface Tailoring Layer for Precise Hydrogen Incorporation and Defect Passivation for High-End Oxide Thin-Film Transistors.

Top-gate self-aligned structured oxide thin-film transistors (TFTs) are suitable for the backplanes of high-end displays because of their low parasitic capacitances. The gate insulator (GI) deposition process should be carefully designed to manufacture a highly stable, high-mobility oxide TFT, particularly for a top-gate structure. In this study, a nanometer-thick Al2O3 layer via plasma-enhanced atomic layer deposition (PE-ALD) is deposited on the top-gate bottom-contact structured oxide TFT as the interface tailoring layer, which can also act as the hydrogen barrier to modulate carrier generation from hydrogen incorporation into the active layer of the TFT during the following process such as postannealing. Al-doped InSnZnO (Al/ITZO) with an Al/In/Sn/Zn atomic ratio composition of 1.7:24.3:40:34 was used for high mobility oxide semiconductors, and an Al2O3/Si3N4 bilayer was used for the GI. The degradation issue due to the excellent barrier characteristics of Al2O3 and Si3N4 can be minimized. An oxide TFT fabricated without the interface tailoring layer exhibits conductor-like characteristics owing to the excessive carrier generation by hydrogen incorporation. However, TFTs with additional interface layers exhibit reasonable characteristics and distinct trends in electrical characteristics depending on the thicknesses of the interface layers. The optimized devices exhibit an average turn-on voltage (Von) of -0.31 V with 33.63 cm2/(V s) of high mobility and 0.09 V/dec of subthreshold swing value. The interfaces between the active layer and hydrogen barriers were investigated using a high-resolution transmission electron microscope, contact angle measurement, and secondary ion mass spectroscopy to reveal the origin of the trends in properties between the devices. The top-gate device with a hydrogen barrier using the four-cycle deposition exhibits optimum electrical characteristics of both high mobility and good stability with only a 0.04 V shift of Von under positive-bias temperature stress (PBTS). We realize a high-end, self-aligned TFT with high mobility [34.7 cm2/(V s)] and negligible Von shift of -0.06 V under PBTS by applying a subnanometer hydrogen barrier.

Interface tailoring through the supply of optimized oxygen and hydrogen to semiconductors for highly stable top-gate-structured high-mobility oxide thin-film transistors.

Self-aligned structured oxide thin-film transistors (TFTs) are appropriate candidates for use in the backplanes of high-end displays. Although SiN x is an appropriate candidate for use in the gate insulators (GIs) of high-performance driving TFTs, direct deposition of SiN x on top of high-mobility oxide semiconductors is impossible due to significant hydrogen (H) incorporation. In this study, we used AlO x deposited by thermal atomic layer deposition (T-ALD) as the first GI, as it has good H barrier characteristics. During the T-ALD, however, a small amount of H from H2O can also be incorporated into the adjacent active layer. In here, we performed O2 or N2O plasma treatment just prior to the T-ALD process to control the carrier density, and utilized H to passivate the defects rather than generate free carriers. While the TFT fabricated without plasma treatment exhibited conductive characteristics, both O2 and N2O plasma-treated TFTs exhibited good transfer characteristics, with a V th of 2 V and high mobility (∼30 cm2 V-1 s-1). Although the TFT with a plasma-enhanced atomic layer deposited (PE-ALD) GI exhibited reasonable on/off characteristics, even without any plasma treatment, it exhibited poor stability. In contrast, the O2 plasma-treated TFT with T-ALD GI exhibited outstanding stability, i.e., a V th shift of 0.23 V under positive-bias temperature stress for 10 ks and a current decay of 1.2% under current stress for 3 ks. Therefore, the T-ALD process for GI deposition can be adopted to yield high-mobility, high-stability top-gate-structured oxide TFTs under O2 or N2O plasma treatment.

Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size.

It is demonstrated that the crystal size of small-molecule organic semiconductors can be controlled during solution shearing by tuning the shape and dimensions of the micropillars on the blade. Increasing the size and spacing of the rectangular pillars increases the crystal size, resulting in higher thin-film mobility. This phenomenon is attributed as the microstructure changing the degree and density of the meniscus line curvature, thereby controlling the nucleation process. The use of allylhybridpolycarbosilane (AHPCS), an inorganic polymer, is also demonstrated as the microstructured blade for solution shearing, which has high resistance to organic solvents, can easily be microstructured via molding, and is flexible and durable. Finally, it is shown that solution shearing can be performed on a curved surface using a curved blade. These demonstrations bring solution shearing closer to industrial applications and expand its applicability to various printed flexible electronics.