High-pressure annealing (HPA) affected the thermodynamics of the formation of a solution-processed oxide film through the simultaneous modification of thermal decomposition and compression, and enabled the use of lower annealing temperatures, which was favourable for device implementation. HPA also reduced the film thickness and decreased the porosity, resulting in enhanced device characteristics at low temperature. Surface and depth profile characterization using X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and ellipsometry suggested that the HPA process supported the effective decomposition of commercial metal-nitrate and/or -salt precursors and strong bonding between oxygen and the metal ions, ultimately reducing the amount of organic residue. The as-optimized HPA process allowed for high-performance solution-processed flexible InZnO (IZO) TFTs on a polymeric substrate at 220 C with low sub-threshold voltage swing (as low as 0.56 V dec À1 ), high on-off ratio of over 10 6 , and fieldeffect mobility as high as 1.78 cm 2 V À1 s À1 , respectively. These results demonstrate that this is a simple and efficient promising approach for improving the performance of solution-processed electronic devices at low temperatures.

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.

Thin-film transistors (TFTs) with a ZrZnSnO (ZZTO) channel layer were fabricated using a solution process. As-prepared ZnSnO (ZTO) TFTs had a large off-current. However, as the content of Zr ions increased in ZTO, the threshold voltage shifted, and the off-current in the TFTs decreased. Because Zr has a lower standard electrode potential, it is more readily oxidized than Sn or Zn. Thus, Zr acted as an effective carrier suppressor in the ZTO system and a ZZTO TFT with a high mobility of a 4.02 cm2 V−1 s−1 and a large on/off ratio of over 106 was achieved.

We investigated the role of Ga in solution-processed InGaZnO thin film transistors (TFTs). The incorporation of Ga into a InZnO compound system results in a decrease in the carrier concentration of the films and an off-current of TFTs. This is a result of the Ga ions forming stronger chemical bonds with oxygen, as compared to the Zn and In ions, acting as a carrier suppressor. It was verified, using X-ray photoelectron spectroscopy (XPS), that the vacancy-related oxygen 1s peak was decreased when the Ga content increased.

Thin-film transistors (TFTs) with multistacked active layers (MSALs) have been studied to improve their electrical performance. The performance enhancement with MSALs has been attributed to higher film density in the effective channel; the density was higher because the porosities of the sublayers were reduced by filling with solution. The proposed TFT with MSALs exhibited an enhanced field-effect mobility of 2.17 cm(2)/(V s) and a threshold voltage shift under positive bias stress of 8.2 V, compared to 1.21 cm(2)/(V s) and 18.1 V, respectively, for the single active layer TFT.

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.

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.

Solution-processed thin-film transistors (TFTs) with La–In–Zn–O (LIZO) as an active channel layer were fabricated with various mole ratios of La. The La3+ additive affected the metal–oxygen bond and made the band gap of LIZO films wider. This behavior indicates that La3+ could play the role of carrier suppressor in InZnO (IZO) systems and significantly reduce the off-current of LIZO films. The optimum LIZO TFT occurred at a LIZO mole ratio of 0.5:5:5 and its channel mobility, threshold voltage, subthreshold swing voltage, and on/off ratio were 2.64 cm2/V s, 7.86 V, 0.6 V/dec, and ∼106, respectively.