Dong Lim Kim

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.

Investigation on the p-type formation mechanism of arsenic doped p-type ZnO thin film

The photoluminescence spectra of As doped p-type ZnO thin films reveal neutral acceptor bound exciton of 3.3437eV and a transition between free electrons and acceptor levels of 3.2924eV. Calculated acceptor binding energy is about 0.1455eV. Thermal activation and doping mechanism of this film have been suggested by the analysis of x-ray photoelectron spectroscopy. p-type formation mechanism of As doped ZnO thin film is related to the AsZn–2VZn complex model. ZnO-based p-n junction was fabricated by the deposition of an undoped n-type ZnO layer on an As doped p-type ZnO layer.

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.

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.

Density-of-States Modeling of Solution-Processed InGaZnO Thin-Film Transistors

The effects of Ga composition on the performance of InGaZnO (IGZO) thin-film transistors (TFTs) prepared by a sol-gel method are investigated, and the density of states (DOS) is characterized by the device modeling. The TFT mode is changed from a depletion type to an enhancement type, and the extracted DOS parameters are reduced with the increase of Ga contents. The extracted DOS distribution has a higher peak value than that of an IGZO TFT prepared by physical vapor deposition.

Improvement in negative bias stress stability of solution-processed amorphous In-Ga-Zn-O thin-film transistors using hydrogen peroxide.

We have investigated the effect of hydrogen peroxide (H2O2) on negative bias stress (NBS) stability of solution-processed amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The instability of solution-processed a-IGZO TFTs under NBS is attributed to intrinsic oxygen vacancy defects (Vo) and organic chemical-induced defects, such as pores, pin holes, and organic residues. In this respect, we added H2O2 into an indium-gallium-zinc oxide solution to reduce the defects without any degradation of electrical performance. The field-effect mobility and sub-threshold slope of the a-IGZO TFTs were improved from 0.37 cm(2) V(-1) s(-1) and 0.86 V/dec to 0.97 cm(2) V(-1) s(-1) and 0.58 V/dec, respectively. Furthermore, the threshold voltage shift under NBS was dramatically decreased from -3.73 to -0.18 V. These results suggest that H2O2 effectively reduces Vo through strong oxidation and minimizes organic chemical-induced defects by eliminating the organic chemicals at lower temperatures compared to a conventional solution process.

Hole Transport Enhancing Effects of Polar Solvents on Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonic acid) for Organic Solar Cells

This study analyzed the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) thin-films prepared by spin-coating solutions made with the polar solvents methanol, acetone, or N,N-dimethylformamide (DMF). A characteristic analysis was carried out for poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM)-based organic solar cells (OSCs) having these modified PEDOT:PSS thin-films as the hole transport layer. The resistivity of the PEDOT:PSS thin-film obtained from the DMF solution was 4.89 × 10(-3) Ω·cm with a roughness of 3.23 × 10° nm, compared to 3.51 × 10(-1) Ω·cm and 7.72 × 10(-1) nm for a pristine PEDOT:PSS thin-film. The dipole moment increase of the solvent led to the decreased resistivity and the increased roughness and transparency of PEDOT:PSS thin-films on the structural arrangement of the polymers. Highly efficient OSCs with a power conversion efficiency of 3.47% were obtained when DMF-treated PEDOT:PSS thin-film was used as the hole transport layer.

Effect of Excimer Laser Annealing on the Performance of Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors

This article reports a method for reducing the contact resistance between amorphous-InGaZnO (a-IGZO) channel and source/drain layer via XeCl excimer laser annealing (ELA) and the device performance of a-IGZO thin-film transistors (TFTs) in terms of laser energy density. The source/drain region in the a-IGZO layer was selectively ELA-treated using a mask, and the resistivity dramatically reduced compared to that of the untreated film (from 10 4 to 10 ―3 Ω cm). Our TFTs had a field-effect mobility of 21.7 cm 2 /V s, an on/off ratio of 1.2 × 10 8 , a threshold voltage of ―0.15 V, and a subthreshold swing of 0.26 V/decade.