Woong Hee Jeong

Effect of indium composition ratio on solution-processed nanocrystalline InGaZnO thin film transistors

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.

Investigation of the effects of Mg incorporation into InZnO for high-performance and high-stability solution-processed thin film transistors

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.

Effect of Zr addition on ZnSnO thin-film transistors using a solution process

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.

Investigating addition effect of hafnium in InZnO thin film transistors using a solution process

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.

Simultaneous modification of pyrolysis and densification for low-temperature solution-processed flexible oxide thin-film transistors

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−1), high on–off ratio of over 106, and field-effect mobility as high as 1.78 cm2 V−1 s−1, 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 effect of La in InZnO systems for solution-processed amorphous oxide thin-film transistors

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.

Improved Electrical Performance of an Oxide Thin-Film Transistor Having Multistacked Active Layers Using a Solution Process

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.

Carrier-suppressing effect of scandium in InZnO systems for solution-processed thin film transistors

The carrier-suppressing effect of Sc in InZnO systems was studied using thin-film transistors (TFTs) with a sol-gel processed active channel. As the amount of Sc content increased, the off current decreased, and the threshold voltage shifted to a positive bias region. The Sc effectively controlled the oxygen vacancies and supplied free electrons. X-ray photoelectron spectroscopy (XPS) verified that the vacancy-related oxygen 1s peak decreased with increasing Sc content. The TFT performance with 14% Sc showed that a field-effect mobility and on-off ratio were 2.06 cm2/V s and 8.02×106, respectively.

Low-Temperature Solution Processing of AlInZnO/InZnO Dual-Channel Thin-Film Transistors

In this letter, we proposed solution-processed AlInZnO (AIZO)/InZnO (IZO) dual-channel thin-film transistors to realize both proper switching behavior and competitive device performance at the low annealing temperature of 350°C. A thin IZO layer provides a higher carrier concentration, thereby maximizing the charge accumulation and yielding high saturation mobility μ_sat, whereas a thick AIZO layer controls the charge conductance resulting in suitable threshold voltage <i>V</i>_th. We therefore obtain excellent device characteristics at 350°C with μ_sat of 1.57 cm²/V ·s, <i>V</i>_th of 1.28 V, an on/off ratio of ~1.4 × 10⁷, and a subthreshold gate swing of 0.59 V/dec.

High-Performance Oxide Thin-Film Transistors Using a Volatile Nitrate Precursor for Low-Temperature Solution Process

Solution-processed InZnO (IZO) thin-film transistors (TFTs) are fabricated using a volatile metal nitrate precursor (Np) with annealing at 300^°C. Because the metal Np decomposes at low temperatures, metal oxide bonds were formed, and the organic residue in the oxide thin films was evaporated at low temperature. At 300^°C , the IZO thin films with Zn Np were of higher quality than those with Zn acetate precursor due to the reduced atomic disorder and evaporation of residual organics. The mobility of the IZO TFTs with Zn Np was 1.92 cm²/V·s at 300^°C annealing.