The effects of the indium content on characteristics of nanocrystalline InGaZnO (IGZO) films grown by a sol-gel method and their thin film transistors (TFTs) have been investigated. Excess indium incorporation into IGZO enhances the field effect mobilities of the TFTs due to the increase in conducting path ways and decreases the grain size and the surface roughness of the films because more InO2− ions induce cubic stacking faults with IGZO. These structural variations result in a decrease in density of interfacial trap sites at the semiconductor-gate insulator interface, leading to an improvement of the subthreshold gate swing of the TFTs.

Solution-processed indium gallium zinc oxide (IGZO) thin films as an active channel layer in thin-film transistors (TFTs) were successfully prepared by a spin-coating method using acetate- and nitrate-based precursors. In the range of 60–130°C , indium, gallium, and zinc precursors were dissociated and then hydrolyzed to metal hydroxides. InGanormalZn2normalO5 compound was synthesized at ∼196°C and crystallized at 305–420°C . A spin-coated IGZO film annealed at 450°C had smooth morphology and fine grains with an average size of ∼15nm . In solution-processed IGZO TFTs using nanocrystalline films prepared at 450°C , the on-to-off ratio, a field effect mobility, and the subthreshold swing voltage were ∼106 , 0.96cm2∕Vs , and 1.39V /decade, respectively.

Zinc‐based metal oxide semiconductors have attracted attention as an alternative to current silicon‐based semiconductors for applications in transparent and flexible electronics. Despite this, metal oxide transistors require significant improvements in performance and electrical reliability before they can be applied widely in optoelectronics. Amorphous indium–zinc–tin oxide (a‐IZTO) has been considered an alternative channel layer to a prototypical indium–gallium–zinc oxide (IGZO) with the aim of achieving a high mobility (>40 cm2 Vs−1) transistors. The effects of the gate bias and light stress on the resulting a‐IZTO field‐effect transistors are examined in detail. Hydrogen impurities in the a‐IZTO semiconductor are found to play a direct role in determining the photo‐bias stability of the resulting transistors. The Al2O3‐inserted IZTO thin‐film transistors (TFTs) are hydrogen‐poor, and consequently show better resistance to the external‐bias‐thermal stress and photo‐bias‐thermal stress than the hydrogen‐rich control IZTO TFTs. First‐principles calculations show that even in the amorphous phase, hydrogen impurities including interstitial H and substitutional H can be bistable centers with an electronic deep‐to‐shallow transition through large lattice relaxation. The negative threshold voltage shift of the a‐IZTO transistors under a negative‐bias‐thermal stress and negative‐bias‐illumination stress condition is attributed to the transition from the acceptor‐like deep interstitial Hi− (or substitutional H‐DX−) to the shallow Hi+ (or HO+) with a high (low) activation energy barrier. Conclusively, the delicate controllability of hydrogen is a key factor to achieve the high performance and stability of the metal oxide transistors.

p -type ZnO films have been fabricated on a (0001) Al2O3 substrate, using Ag2O as a silver dopant by pulsed laser deposition. The structural property of those films is systematically characterized by observing the shift of (0002) peak to investigate the substitution of Ag+ for Zn+. Narrow deposition temperature for Ag-doped p-type ZnO films has been obtained in the range of 200–250°C with the hole concentration of 4.9×1016–6.0×1017cm−3. A neutral acceptor bound exciton has been clearly observed by photoluminescence emitted at 3.317eV in Ag-doped p-type ZnO thin films.

Persistent photoconduction (PPC) is a phenomenon that limits the application of oxide semiconductor thin-film transistors (TFTs) in optical sensor-embedded displays. In the present work, a study on zinc oxynitride (ZnON) semiconductor TFTs based on the combination of experimental results and device simulation is presented. Devices incorporating ZnON semiconductors exhibit negligible PPC effects compared with amorphous In-Ga-Zn-O (a-IGZO) TFTs, and the difference between the two types of materials are examined by monochromatic photonic C-V spectroscopy (MPCVS). The latter method allows the estimation of the density of subgap states in the semiconductor, which may account for the different behavior of ZnON and IGZO materials with respect to illumination and the associated PPC. In the case of a-IGZO TFTs, the oxygen flow rate during the sputter deposition of a-IGZO is found to influence the amount of PPC. Small oxygen flow rates result in pronounced PPC, and large densities of valence band tail (VBT) states are observed in the corresponding devices. This implies a dependence of PPC on the amount of oxygen vacancies (VO). On the other hand, ZnON has a smaller bandgap than a-IGZO and contains a smaller density of VBT states over the entire range of its bandgap energy. Here, the concept of activation energy window (AEW) is introduced to explain the occurrence of PPC effects by photoinduced electron doping, which is likely to be associated with the formation of peroxides in the semiconductor. The analytical methodology presented in this report accounts well for the reduction of PPC in ZnON TFTs, and provides a quantitative tool for the systematic development of phototransistors for optical sensor-embedded interactive displays.

We have fabricated high-performance and high-stability sol-gel-processed MgInZnO thin films transistors with varying Mg content. As the Mg content was increased, the turn-on-voltage increased and the off-current decreased. This is because the incorporation of Mg (with low standard electrode potential and high optical band gap, Eopt, when oxidized) causes reduction in the oxygen vacancy, acting as a carrier source, and an increase in Eopt of the film. This results in reduction in carrier concentration of the film. Small grains and smooth morphology by varying the Mg content lead to an improvement of the mobility, on-current, and subthreshold gate swing.

Indium–gallium–zinc oxide (IGZO) films, deposited by sputtering at room temperature, still require activation to achieve satisfactory semiconductor characteristics. Thermal treatment is typically carried out at temperatures above 300 °C. Here, we propose activating sputter- processed IGZO films using simultaneous ultraviolet and thermal (SUT) treatments to decrease the required temperature and enhance their electrical characteristics and stability. SUT treatment effectively decreased the amount of carbon residues and the number of defect sites related to oxygen vacancies and increased the number of metal oxide (M–O) bonds through the decomposition-rearrangement of M–O bonds and oxygen radicals. Activation of IGZO TFTs using the SUT treatment reduced the processing temperature to 150 °C and improved various electrical performance metrics including mobility, on-off ratio, and threshold voltage shift (positive bias stress for 10,000 s) from 3.23 to 15.81 cm2/Vs, 3.96 × 107 to 1.03 × 108, and 11.2 to 7.2 V, respectively.

The effects of adding Hf into a InZnO (IZO) system, particularly the electrical characteristics of their thin film and thin film transistors (TFTs), were investigated as a function of atomic concentration from 0 to 10 at. % of Hf and Ga/Zn. Because Hf has a high affinity for oxygen in IZO system, the Hf suppresses carrier generation more effectively than does Ga. At 10 at. % of Hf/Zn atomic concentration, the HfInZnO TFTs showed wider on-to-off ratios than those of GaInZnO TFTs due to the low standard-electrode-potential of Hf and sharp subthreshold swings due to low trap density.