Solution-processed bilayer InGaZnO/In2O3thin film transistors at low temperature by lightwave annealing

At low temperatures about 230 °C, bilayer InGaZnO/In2O3thin film transistors (TFTs) were prepared by a solution process with lightwave annealing. The InGaZnO/In2O3bilayer TFTs with SiO2as dielectric layer show high electrical performances, such as a mobility of 7.63 cm2V-1s-1, a threshold voltage (Vth) of 3.8 V, and an on/off ratio higher than 107, which are superior to single-layer InGaZnO TFTs or In2O3TFTs. Moreover, bilayer InGaZnO/In2O3TFTs demonstrated a great bias stability enhancement due to the introduction of top InGaZnO film act as a passivation layer, which could prevent the interaction of ambient air with the bottom In2O3layer. By using high dielectric constant AlOxfilm, the InGaZnO/In2O3TFTs exhibit an improved mobility of 47.7 cm2V-1s-1. The excellent electrical performance of the solution-based InGaZnO/In2O3TFTs shows great application potential for low-cost flexible printed electronics.

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.

Effects of Post-UV/Ozone Treatment on Electrical Characteristics of Solution-Processed Copper Oxide Thin-Film Transistors

To realize oxide semiconductor-based complementary circuits and better transparent display applications, the electrical properties of p-type oxide semiconductors and the performance improvement of p-type oxide thin-film transistors (TFTs) are required. In this study, we report the effects of post-UV/ozone (O₃) treatment on the structural and electrical characteristics of copper oxide (CuO) semiconductor films and the TFT performance. The CuO semiconductor films were fabricated using copper (II) acetate hydrate as a precursor material to solution processing and the UV/O₃ treatment was performed as a post-treatment after the CuO film was fabricated. During the post-UV/O₃ treatment for up to 13 min, the solution-processed CuO films exhibited no meaningful change in the surface morphology. On the other hand, analysis of the Raman and X-ray photoemission spectra of solution-processed CuO films revealed that the post-UV/O₃ treatment induced compressive stress in the film and increased the composition concentration of Cu-O lattice bonding. In the post-UV/O₃-treated CuO semiconductor layer, the Hall mobility increased significantly to approximately 280 cm² V^-1 s^-1, and the conductivity increased to approximately 4.57 × 10^-2 Ω^-1 cm^-1. Post-UV/O₃-treated CuO TFTs also showed improved electrical properties compared to those of untreated CuO TFTs. The field-effect mobility of the post-UV/O₃-treated CuO TFT increased to approximately 6.61 × 10^-3 cm^-2 V^-1 s^-1, and the on-off current ratio increased to approximately 3.51 × 10³. These improvements in the electrical characteristics of CuO films and CuO TFTs can be understood through the suppression of weak bonding and structural defects between Cu and O bonds after post-UV/O₃ treatment. The result demonstrates that the post-UV/O₃ treatment can be a viable method to improve the performance of p-type oxide TFTs.

Cation Composition-Dependent Device Performance and Positive Bias Instability of Self-Aligned Oxide Semiconductor Thin-Film Transistors: Including Oxygen and Hydrogen Effect

Amorphous oxide semiconductor transistors control the illuminance of pixels in an ecosystem of displays from large-screen TVs to wearable devices. To satisfy application-specific requirements, oxide semiconductor transistors of various cation compositions have been explored. However, a comprehensive study has not been carried out where the influence of cation composition, oxygen, and hydrogen on device characteristics and stability is systematically quantified, using commercial-grade process technology. In this study, we fabricate self-aligned top-gate structure thin-film transistors with three oxide semiconductor materials, InGaZnO (In/Ga/Zn = 1:1:1), In-rich InGaZnO, and InZnO, having mobility values of 10, 27, and 40 cm²/V·s, respectively. Combinations of varied amounts of oxygen and hydrogen are incorporated into each transistor by controlling the fabrication process to study the effect of these gaseous elements on the physical nature of the channel material. Electrons can be captured by peroxy linkage (O₂^2-) or undercoordinated In (In* to become In⁺), which are manifested in the extracted subgap density-of-states profile and first-principles calculations. Energy difference between electron-trapped In⁺ and O₂^2- σ* is the smallest for IGZO, and In⁺-O₂^2- annihilation occurs by electron excitation from the subgap In⁺ state to the O₂^2- σ*. Furthermore, characteristic time constants during positive bias stress and recovery reveal the various microscopic physical phenomena within the transistor structure between different cation compositions.

Stabilization of the Surface of ZnO Films and Elimination of the Aging Effect

Zinc oxide is a promising multifunctional material. The practical use of nano- and polycrystalline ZnO devices faces a serious problem of instability of electrical and luminescent characteristics, due to the adsorption of oxygen by the surface during aging. In this paper, the aging effect in ZnO films and nanorod arrays was studied. It was found that ZnO samples demonstrate different behavior of the degradation process, which corresponds to at least two different types of adsorbing surface sites for O₂, where O₂ adsorption is of a different nature. The first type of surface sites is rapidly depassivated after hydrogen passivation and the aging effect takes place due to these centers. The second type of surface sites has a stable structure after hydrogen passivation and corresponds to HO-ZnO sites. The XPS components of these sites include the Zn2p_3/2 peak at 1022.2 ± 0.2 eV and Zn2p_1/2 peak at 1045.2 ± 0.2 eV, with a part of the XPS O1s peak at 531.5 ± 0.3 eV. The annealing transforms the first type of site into the second one, and the subsequent short-term plasma treatment in hydrogen results in steady passivation, where the degradation of characteristics is practically reduced to zero.