The effect of surface energy characterized functional groups of self-assembled monolayers for enhancing the electrical stability of oxide semiconductor thin film transistors.

The exact direction of the surface energy characterized functional groups of self-assembled monolayers (SAMs) is proposed for achieving enhanced electrical stability of indium gallium zinc oxide (IGZO) semiconductor thin film transistors (TFTs). The SAM treatment, particularly with the SAM functional group having lower surface energy, makes it difficult to adsorb oxygen molecules difficult onto IGZO. Such an effect greatly improves the positive bias stability (PBS) and clockwise hysteresis stability. For NH2 and CF3 functional groups, SAMs with surface energies of 49.4 mJ m-2 and 23.5 mJ m-2, respectively, improved the IGZO TFT PBS from 2.47 V to 0.32 V after the SAM treatment and the IGZO TFT clockwise hysteresis was also enhanced from 0.23 V to 0.11 V without any deterioration of TFT characteristics. Employing lower surface energy functional groups to the SAM, of the same head and body groups, passivates and protects the IGZO backchannel region from oxygen molecules in the atmosphere. Consequently, the enhanced electrical stability of IGZO TFTs can be achieved by the simple and economic SAM treatment.

The effect of Surface energy characterized functional group of self-assembled monolayer for enhancing electrical stability of oxide semiconductor thin film transistor.

The exact direction, of the surface energy characterized functional group of self-assembled monolayer (SAM), is proposed for achieving the enhanced electrical stability of indium gallium zinc oxide (IGZO) semiconductor thin film transistor (TFT). The SAM treatment, particularly at the SAM functional group having lower surface energy, makes oxygen molecules difficult to be adsorbed onto IGZO. And such an effect much improves positive bias stability (PBS) and clockwise hysteresis stability to the same tendency. For NH2 and CF3 functional group SAMs with surface energies of 49.4 mJ/m2 and 23.5 mJ/m2, respectively, the IGZO TFT PBS was improved from 2.47 V to 0.32 V after the SAM treatment and the IGZO TFT clockwise hysteresis was also enhanced from 0.23 V to 0.11 V without any deterioration of TFT characteristics. Employing lower surface energy functional group to the SAM, of same head group and body group, does passivate and protect the IGZO backchannel region from oxygen molecules in the atmosphere. Consequently, the enhanced electrical stability of IGZO TFT can be achieved by the simple and economic SAM treatment.

Atmospheric-pressure plasma treatment toward high-quality solution-processed aluminum oxide gate dielectric films in thin-film transistors.

We present an atmospheric-pressure plasma (APP) treatment technique to improve the electrical performance of solution-processed dielectric films. This technique can successfully reduce leakage current and frequency dependence of solution-processed dielectric films. The APP treatment contributes to the conversion of metal hydroxide to metal oxide, and in the case of a solution-treated AlO x dielectric thin film, it effectively ascribes to the formation of high-quality AlO x dielectric thin films. The capacitance of the untreated AlO x dielectric thin film varies up to 9.9% with frequency change, but the capacitance of the APP treated AlO x dielectric thin film varies within 1.5%. When the solution-processed InO x thin-film transistors (TFTs) were fabricated using these dielectric films, the field-effect mobility of TFTs with the APP-treated AlO x dielectric film was increased significantly from 9.77 to 26.79 cm2 V-1 s-1 in comparison to that of TFTs with the untreated AlO x dielectric film. We also have confirmed that these results are similar to the properties of the sample prepared at high annealing temperature including electrical performance, conduction mechanism and chemical structure. The APP treatment technique provides a new opportunity to effectively improve the electrical performance of solution-processed dielectrics in the atmosphere at low temperature.

Conductive Polymer-Assisted Metal Oxide Hybrid Semiconductors for High-Performance Thin-Film Transistors.

Metal oxide semiconductors doped with additional inorganic cations have insufficient electron mobility for next-generation electronic devices so strategies to realize the semiconductors exhibiting stability and high performance are required. To overcome the limitations of conventional inorganic cation doping to improve the electrical characteristics and stability of metal oxide semiconductors, we propose solution-processed high-performance metal oxide thin-film transistors (TFTs) by incorporating polyaniline (PANI), a conductive polymer, in a metal oxide matrix. The chemical interaction between the metal oxide and PANI demonstrated that the defect sites and crystallinity of the semiconductor layer are controllable. In addition, the change in oxygen-related chemical bonding of PANI-doped indium oxide (InOx) TFTs induces superior electrical characteristics compared to pristine InOx TFTs, even though trace amounts of PANI are doped in the semiconductor. In particular, the average field-effect mobility remarkably enhanced from 15.02 to 26.58 cm2 V-1 s-1, the on/off current ratio improved from 108 to 109, and the threshold voltage became close to 0 V actually from -7.9 to -1.4 V.

Analysis of Interface Phenomena for High-Performance Dual-Stacked Oxide Thin-Film Transistors via Equivalent Circuit Modeling.

Oxide thin-film transistors (TFTs) have attracted much attention because they can be applied to flexible and large-scaled switching devices. Especially, oxide semiconductors (OSs) have been developed as active layers of TFTs. Among them, indium-gallium-zinc oxide (IGZO) is actively used in the organic light-emitting diode display field. However, despite their superior off-state properties, IGZO TFTs are limited by low field-effect mobility, which critically affects display resolution and power consumption. Herein, we determine new working mechanisms in dual-stacked OS, and based on this, we develop a dual-stacked OS-based TFT with improved performance: high field-effect mobility (∼80 cm2/V·s), ideal threshold voltage near 0 V, high on-off current ratio (>109), and good stability at bias stress. Induced areas are formed at the interface by the band offset: band offset-induced area (BOIA) and BOIA-induced area (BIA). They connect the gate bias-induced area (GBIA) and electrode bias-induced area (EBIA), resulting in high current flow. Equivalent circuit modeling and the transmission line method are also introduced for more precise verification. By verifying current change with gate voltage in the single OS layer, the current flowing direction in the dual-stacked OS is calculated and estimated. This is powerful evidence to understand the conduction mechanism in a dual-stacked OS-based TFT, and it will provide new design rules for high-performance OS-based TFTs.

Titanium dioxide surface modification via ion-beam bombardment for vertical alignment of nematic liquid crystal.

We introduce the characteristics of the titanium dioxide (TiO(2)) inorganic film deposited by rf magnetron sputtering for liquid crystal display applications. The TiO(2) films demonstrated vertical alignment (VA) of the liquid crystals (LCs) obtained by using ion-beam (IB) bombardment. As observed by using x-ray photoelectron spectroscopy, the chemical structure of the TiO(2) was changed by IB bombardment, altering the Ti-O bonding of the Ti 2p spectra to lower intensity levels. Breaking Ti-O bonding by IB bombardment created pretilt angles between the TiO(2) film and LC molecules. The better voltage-transmittance characteristics of the VA LCDs based on TiO(2) film were measured and compared with the same characteristics of polyimide film.

Low-power operation of vertically aligned liquid-crystal system via anatase-TiO(2) nanoparticle dispersion.

Electro-optic performance of a liquid-crystal (LC) system is enhanced by TiO(2) nanoparticle dispersed in nematic liquid crystal (NLC). The 2.5 V threshold voltage of LC for device operation is lowered to 0.5 V through TiO(2) nanoparticle mixing up to 2 wt.%. To characterize the shape and size distribution of the nanoparticles, high-resolution transmission electron microscopy is employed. Transmittance spectra for the TiO(2) dispersed LC structure and nondispersed LC structure showed that transparency of the TiO(2) dispersed LC is similar to that of pure liquid LC.