k-Jun Seo

High performance solution-processed amorphous zinc tin oxide thin film transistor

Thin film transistors (TFTs) with amorphous zinc tin oxide (ZTO) channel layer were fabricated by a simple and low-cost solution process. The ZTO thin films are highly transparent (>90% transmittance) in the visible region. The ZTO TFTs fabricated at 400 and 500 °C are operated in enhancement mode. The TFT annealed at 500 °C shows a mobility of 14.11 cm2 V−1 s−1, a threshold voltage of 1.71 V, a subthreshold slope of 0.4 V dec−1 and an on–off current ratio greater than 108. In addition, we investigated the gate bias stability of the TFT. Positive gate bias results in a positive shift of the threshold voltage due to the charge trapping in the channel/dielectric interface.

Solution-Processed Indium-Zinc Oxide Transparent Thin-Film Transistors

Transparent thin-film transistors (TTFTs) with an indium-zinc oxide (IZO) active layer by the solution-processed deposition method were fabricated and their TFT characterization was examined. Solution-processed IZO thin films were amorphous and highly transparent with >90% transmittance in the visible region with an optical bandgap of 3.1 eV. Spin-coated IZO TTFTs were operated in depletion mode and showed a field-effect mobility as high as 7.3 cm 2 /V s, a threshold voltage of 2.5 V, an on/off current ratio greater than 10 7 , and a subthreshold slope of 1.47 V/decade.

Er3+ luminescence and cooperative upconversion in ErxY2−xSiO5 nanocrystal aggregates fabricated using Si nanowires

Er3+ luminescence and cooperative upconversion in ErxY2−xSiO5 nanocrystal aggregates fabricated using Si nanowires is investigated. X-ray diffraction and photoluminescence spectroscopy indicate that the composition of the final nanocrystals can be varied continuously from pure Y2SiO5 to pure Er2SiO5 while keeping the crystal structure the same. Analysis of concentration and pump-power dependence of the Er3+ photoluminescence intensity and decay time shows that while cooperative upconversion occurs at high Er concentrations, the cooperative upconversion coefficient is only (2.2±1.1)×10−18cm3∕s at a Er concentration of 1.2×1021cm−3. This is nearly ten times lower at more than ten times higher Er concentration than that reported from Er-doped silica and demonstrates the viability of using such silicates for compact, high-gain Si-based optical material for Si photonics.

Large-scale fabrication of single-phase Er2SiO5 nanocrystal aggregates using Si nanowires

Single-phase Er2SiO5 nanocrystal aggregates were produced on a large scale using Si nanowire (Si-NW) arrays as templates. A dense array of Si-NWs was grown by vapor-liquid-solid mechanism using Au catalyst on Si (111) substrate. Afterwards, ErCl3∙6H2O dissolved ethanol solution was spin coated and annealed first at 900°C for 4min in a flowing N2∕O2 environment and then at 1200°C in a flowing Ar environment for 3min. X-ray diffraction, scanning electron microscope, and high-resolution transmission electron microscope measurements indicate that due to the use of Si-NWs, such a short annealing procedure is sufficient to completely transform the Er-coated Si-NWs into a thick, large-area aggregate of pure, single-phase to Er2SiO5 oxyorthosilicate nanocrystals. The crystalline nature of Er2SiO5 film and the loose nature of the aggregate result in an atomlike Er3+ spectrum with a very narrow luminescence linewidth at 1.53μm, which together with a complete lack of temperature quenching of Er3+ luminescence and a ...

Postannealing Process for Low Temperature Processed Sol–Gel Zinc Tin Oxide Thin Film Transistors

We fabricated zinc tin oxide (ZTO) thin film transistors (TFTs) using a stable ZTO sol―gel solution at a low annealing temperature of 300°C. To enhance transistor performance, the ZTO films were postannealed under vacuum and wet air consecutively. The vacuum and wet air postannealed ZTO TFTs exhibited high saturation mobilities (5.5 cm 2 /V s), low subthreshold swing (0.38 V/dec), and high on―off current ratio (8 × 10 8 ). We analyzed the ZTO films before and after postannealing by X-ray photoelectron spectroscopy to explain the origin of the enhanced performance.

Fabrication and characterization of sol-gel-derived zinc oxide thin-film transistor

Thin-film transistors (TFTs) with zinc oxide channel layers were fabricated through a simple and low-cost solution process. Precursor solution concentration, annealing temperature, and the process were controlled for the purpose of improving the electrical properties of ZnO TFTs and analyzed in terms of microstructural scope. The fabricated ZnO films show preferential orientation of the (002) plane, which contributes to enhanced electron conduction and a dense surface. The results show that the TFT characteristics of the film are clearly affected by the microstructure. The optimized TFT operates in a depletion mode, shows n-type semiconductor behavior, and is highly transparent (>90%) within the visible light

Improved negative bias illumination instability of sol-gel gallium zinc tin oxide thin film transistors

We investigated the Ga doping effect on the performance and negative bias illumination instability of sol-gel zinc tin oxide (ZTO) thin film transistors (TFTs). The performance of the Ga doped ZTO (GZTO) TFTs is controlled and optimized by the concentration of Ga ions, which suppress the formation of oxygen vacancies. The negative bias illumination instability of the devices with a sol-gel hybrid material passivation layer is compared through a time-evolution stress analysis and illumination wavelength dependence measurements. The GZTO TFT exhibits improved stability relative to the ZTO TFT, because Ga ions effectively decrease charge trapping sites originating from oxygen vacancies.

A selective fluorescent probe for cysteine and its imaging in live cells

A probe for the detection of cysteine over homocysteine based on 2-(2′-hydroxyphenyl)benzothiazole (HBT) was prepared and used in confocal microscopy experiments. The probe was designed to block excited state intramolecular proton transfer (ESIPT). When bromopropionyl group protection is removed, HBT is recovered via nucleophilic substitution and intramolecular cyclization. The probe was found to have a detection limit of 2.8 μM and exhibits a ∼20-fold increase. The probe showed cell membrane permeability and efficacy in living Hep3B cells.

Improvement of photo-induced negative bias stability of oxide thin film transistors by reducing the density of sub-gap states related to oxygen vacancies

The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-induced negative bias stability of the resulting thin film transistors were studied. As the indium ratio increases, optical absorption via sub-gap states increases, and the threshold voltage degradation under negative bias temperature stress (NBTS) with light illumination becomes more severe. By applying high pressure anneal treatments in oxygen ambient, the density of sub-gap states is reduced by an order of magnitude compared to air-annealed devices. Consequently, significant improvements are observed in the threshold voltage shifts and the stretched exponential parameters under NBTS with light illumination.

Effects of Sol-Gel Organic-Inorganic Hybrid Passivation on Stability of Solution-Processed Zinc Tin Oxide Thin Film Transistors

We fabricated solution-processed zinc tin oxide (ZTO) TFTs with sol-gel organic-inorganic hybrid passivation layers owing to their solution-processibility and good water and oxygen barrier property. The sol-gel organic-inorganic hybrid passivation layers reduce hysteresis of the TFTs without deterioration of performance. The gate bias stability and the environmental stability under high temperature and relative humidity are also improved compared to unpassivated and poly(methyl methacrylate) (PMMA) passivated TFTs. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3603845] All rights reserved.