Jun Hyung Lim

Solution-processed InGaZnO-based thin film transistors for printed electronics applications

This letter reports the utility of using the sol-gel process for exploring the library of multicomponent ZnO-based oxides as an active layer of thin film transistors. We chose InGaZnO as a starting material and modulated the Ga content to examine the potential of this material. Increasing the Ga ratio from 0.1 to 1 brought about a dynamic shift in the electrical behavior from conductor to semiconductor. This exploratory work critically helped us fabricate a device with robust device performance (a mobility of 1∼2 cm2 V−1 s−1 for the 400 °C-sintered samples and 0.2 cm2 V−1 s−1 for the 300 °C-sintered samples).

Effect of annealing temperature on microstructural evolution and electrical properties of sol-gel processed ZrO2/Si films

High-permittivity (k) ZrO2/Si(100) films were fabricated by a sol-gel technique and the microstructural evolution with the annealing temperature (Ta) was correlated with the variation of their electrical performance. With increasing Ta, the ZrO2 films crystallized into a tetragonal (t) phase which was maintained until 700 °C at nanoscale thicknesses. Although the formation of the t-ZrO2 phase obviously enhanced the k value of the ZrO2 dielectric layer, the maximum capacitance in accumulation was decreased by the growth of a low-k interfacial layer (IL) between ZrO2 and Si with increasing Ta. On the other hand, the gate leakage current was remarkably depressed with increasing Ta probably due to the combined effects of the increased IL thickness, optical band gap of ZrO2, and density of ZrO2 and decreased remnant organic components.

Hydrothermally Grown In-doped ZnO Nanorods on p-GaN Films for Color-tunable Heterojunction Light-emitting-diodes

The incorporation of doping elements in ZnO nanostructures plays an important role in adjusting the optical and electrical properties in optoelectronic devices. In the present study, we fabricated 1-D ZnO nanorods (NRs) doped with different In contents (0% ~ 5%) on p-GaN films using a facile hydrothermal method, and investigated the effect of the In doping on the morphology and electronic structure of the NRs and the electrical and optical performances of the n-ZnO NRs/p-GaN heterojunction light emitting diodes (LEDs). As the In content increased, the size (diameter and length) of the NRs increased, and the electrical performance of the LEDs improved. From the electroluminescence (EL) spectra, it was found that the broad green-yellow-orange emission band significantly increased with increasing In content due to the increased defect states (oxygen vacancies) in the ZnO NRs, and consequently, the superposition of the emission bands centered at 415 nm and 570 nm led to the generation of white-light. These results suggest that In doping is an effective way to tailor the morphology and the optical, electronic, and electrical properties of ZnO NRs, as well as the EL emission property of heterojunction LEDs.

Effect of dual frequency on the plasma characteristics in an internal linear inductively coupled plasma source

An internal-type linear inductive antenna, referred to as a “double comb-type antenna,” was used as a large area plasma source with a substrate size of 880×660mm2 (fourth generation glass size). The effects of the dual frequency (2 and 13.56MHz) radio frequency (rf) power to the antenna as well as the power ratio on the plasma characteristics were investigated. High-density plasma on the order of 1.7×1011cm−3 could be obtained with a dual frequency power of 5kW (13.56MHz) and 1kW (2MHz) at a pressure of 15mTorr Ar. This plasma density was lower than that obtained for the double comb-type antenna using a single frequency alone (5kW, 13.56MHz). However, the use of the dual frequency with a rf power ratio of approximately 1(2MHz):5(13.56MHz) showed better plasma uniformity than that obtained using the single frequency. Plasma uniformity of 6.1% could be obtained over the substrate area. Simulations using FL2L code confirmed the improvement in the plasma uniformity using the dual frequency to the double comb-...

Characteristics of Ce-Doped ZrO2 Dielectric Films Prepared by a Solution Deposition Process

The microstructural and electrical properties of sol-gel deposited ultrathin Zr 1―x Ce x O 2 films with different Ce contents (x = 0, 0.1, 0.3, and 0.5) were studied using various characterization tools. Ce doping reduced the crystallization (densification) temperature and increased the dielectric constant of the Zr 1―x Ce x O 2 film. There was no degradation of the hysteresis characteristics, and a systematic negative shift in the flatband voltage was observed by incorporating Ce atoms. Leakage current measurements showed no detrimental effects of Ce doping up to x = 0.5, and the conduction mechanism analyses revealed that the Zr 1―x Ce x O 2 films follow a Poole-Frenkel (PF) conduction, exhibiting a systematic increase in the linear slope of the PF plot possibly due to the decrease in dielectric trap sites with increasing Ce content.

Effect of Al2O3 Deposition on Performance of Top-Gated Monolayer MoS2-Based Field Effect Transistor

Deposition of high-k dielectrics on two-dimensional MoS2 is an important process for successful application of the transition-metal dichalcogenides in electronic devices. Here, we show the effect of H2O reactant exposure on monolayer (1L) MoS2 during atomic layer deposition (ALD) of Al2O3. The results showed that the ALD-Al2O3 caused degradation of the performance of 1L MoS2 field effect transistors (FETs) owing to the formation of Mo-O bonding and trapping of H2O molecules at the Al2O3/MoS2 interface. Furthermore, we demonstrated that reduced duration of exposure to H2O reactant and postdeposition annealing were essential to the enhancement of the performance of top-gated 1L MoS2 FETs. The mobility and on/off current ratios were increased by factors of approximately 40 and 103, respectively, with reduced duration of exposure to H2O reactant and with postdeposition annealing.

Selective plasma etching of ZrOx to Si using inductively coupled BCl3∕C4F8 plasmas

In this study, the etch characteristics of ZrOx and the etch selectivity to Si were investigated using BCl3∕C4F8 plasmas. The etching mechanism was also investigated. Increasing the C4F8 percentage to 4% formed a C–F polymer layer on the silicon surface due to the increased flux ratio of CFx∕F to the substrate, while no such C–F polymer was formed on the ZrOx surface due to the removal of carbon from CFx by the oxygen in ZrOx. By using 3–4% C4F8 in the BCl3∕C4F8 mixture, infinite etch selectivity of ZrOx to silicon and photoresist could be obtained while maintaining the ZrOx etch rate above 400A∕min.

Synergistic effect of Indium and Gallium co-doping on growth behavior and physical properties of hydrothermally grown ZnO nanorods

We synthesized ZnO nanorods (NRs) using simple hydrothermal method, with the simultaneous incorporation of gallium (Ga) and indium (In), in addition, investigated the co-doping effect on the morphology, microstructure, electronic structure, and electrical/optical properties. The growth behavior of the doped NRs was affected by the nuclei density and polarity of the (001) plane. The c-axis parameter of the co-doped NRs was similar to that of undoped NRs due to the compensated lattice distortion caused by the presence of dopants that are both larger (In3+) and smaller (Ga3+) than the host Zn2+ cations. Red shifts in the ultraviolet emission peaks were observed in all doped NRs, owing to the combined effects of NR size, band gap renormalization, and the presence of stacking faults created by the dopant-induced lattice distortions. In addition, the NR/p-GaN diodes using co-doped NRs exhibited superior electrical conductivity compared to the other specimens due to the increase in the charge carrier density of NRs and the relatively large effective contact area of (001) planes. The simultaneous doping of In and Ga is therefore anticipated to provide a broader range of optical, physical, and electrical properties of ZnO NRs for a variety of opto-electronic applications.

Cryogenic System for 80-kV DC HTS Cable in the KEPCO Power Grid

DC HTS cable has advantages in the absence of ac loss. Therefore, the Korea Electric Power Corporation (KEPCO) has started a project of operating and manufacturing technology for applying an 80-kV 500-MW 500-m-long dc HTS cable to the commercial power grid since 2011. LS Cable Ltd. has joined this project for designing and manufacturing an HTS power cable, and KEPCO has taken on cryogenic system and real power grid operation. The cryogenic system for an 80-kV dc HTS cable is composed mainly of Stirling-type cryocoolers. The Stirling cryocooler has been examined and verified by real grid operation in Icheon substation, and we therefore became assured of reliability for the cooling HTS cable system. We present the cryogenic system design, installation, and some results of preliminary tests in this paper.

Effect of W addition on the microstructure and properties of Ni-W substrates for coated conductors

We fabricated Ni and Ni-W alloys for use as substrates in YBCO coated conductor applications and evaluated the effects of the W addition on the texture, microstructure, and mechanical and magnetic properties of the substrate. Pure Ni and Ni-W (2, 3, and 5 at.%) alloys were prepared by plasma arc melting and then cold rolled and annealed in the temperature range of 600-1300/spl deg/C. The texture of the substrates was evaluated by pole-figure and orientation distribution function (ODF) analysis. The magnetic properties were also evaluated using the physical property measurement system (PPMS). It was observed that the Ni-W substrates had a stronger cube texture and a wider annealing temperature range in which the cube texture became stable than those of the pure Ni substrate. The full-width at half-maximums (FWHMs) of in-plane texture for the Ni-W substrate were 4.42/spl deg/-5.57/spl deg/ at an annealing temperature of 800/spl deg/C-1300/spl deg/C, while that of pure Ni was 9.5/spl deg/ at 800/spl deg/C. Therefore, it is considered that the addition of W enhances the formation of the cube texture and improves the texture stability at higher annealing temperatures. In addition, the Ni-W substrates had a smaller grain size and higher mechanical strength and hardness, as compared to those of the pure Ni substrate. These improvements are probably due to various strengthening mechanisms, such as solid solution hardening and/or grain size strengthening. PPMS analysis showed that the addition of W effectively reduced the saturation magnetization in an applied magnetic field, as well as the Curie temperature.