• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.5.2-5.2
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• 2009

From 10 years ago, the development of nano-devices endeavored to achieve reconstruction of information technology (IT) and nano technology (NT) industry. Among the many materials for the IT and NT industry, zinc oxide (ZnO) is a very promising candidate material for the research of nano-device development. Nano-structures of ZnO-based materials were grown easily via various methods and it attracts huge attention because of their superior electrical and optical properties for optoelectronic devices. Recently, among the various growth methods, MOCVD has attracted considerable attention because it is suitable process with benefits such as large area growth, vertical alignment, and accurate doping for nano-device fabrication. However, ZnO based nanowires grown by MOCVD process were had the principal problems of 1st interfacial layers between substrate and nanowire, 2nd a broad diameter (about 100 nm), and 3rd high density, and 4th critical evaporation temperature of Zinc precursors. In particular, the growth of high performance nanowire for high efficiency nano-devices must be formed at high temperature growth, but zinc precursors were evaporated at high temperature.These problems should be repaired for materialization of ultra high performance quantum devices with quantum effect. For this reason, we firstly proposed the growth method of vertical aligned slim MgZnO nanowires (< 10 nm) without interfacial layers using self-phase separation by introduced Mg at critical evaporation temperature of Zinc precursors ($500^{\circ}C$). Here, the self-phase separation was reported that MgO-rich and the ZnO-rich phases were spontaneously formed by additionally introduced Mg precursors. In the growth of nanowires, the nanowires were only grown on the wurzite single crystal seeds as ZnO-rich phases with relatively low Mg composition (~36 at %). In this study, we investigated the microstructural behaviors of self-phase separation with increasing the Mg fluxes in the growth of MZO NWs, in order to secure drastic control engineering of density,diameter, and shape of nanowires.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.235-240
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• 2010

We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of $500^{\circ}C$. It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at $250^{\circ}C$ and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.8
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• pp.602-607
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• 2013

Concern for the TOS (Transparent Oxide Semiconductor) is increasing with the recent increase in interest for flexible device. Especially MgZnO has attracted a lot of attention. $Mg_xZn_{1-x}O$, which ZnO-based wideband-gap alloys is tuneable the band-gap ranges from 3.36 eV to 7.8 eV. In particular, the flexible substrate, the crystal structure of the amorphous as well as the surface morphology is not good. So research of MgZnO thin films growth on flexible substrate is essential. Therefore, in this study, we studied on the effects of the oxygen partial pressure on the structural and crystalline of $Mg_{0.1}Zn_{0.9}O$ thin films. MgZnO thin films were deposited on PES substrate by using pulsed laser deposition. We used XRD and AFM in order to observe the structural characteristics of MgZnO thin films. UV-visible spectrophotometer was used to get the band gap and transmittance. Crystallization was done at a low oxygen partial pressure. The crystallinity of MgZnO thin films with increasing temperature was improved, Grain size and RMS of the films were increased. MgZnO thin films showed high transmittance over 80% in the visible region.

• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.162-167
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• 2023

Diverse structures of Mn oxides in natural and engineered systems occur from the transformation of δ-MnO₂, the most common crystalline phase of nucleated Mn oxides, to other structures via redox reactions, adsorption of metals, etc. Recently, together with emerging interests of Zn-based rechargeable battery systems, which use Mn oxides as a cathode, the transformation and recrystallization of Mn oxides have garnered interests. Here, using hydrothermal reaction of Zn-doped δ-MnO₂, the formation of todorokite and chalcophanite is observed. When the concentration of doped Zn increases, the formation of chalcophanite is dominant, but occurs slower than that of the lower concentration of doped Zn. This study will provide a new understanding of the effect of Zn on the recrystallization process of Mn oxides during redox cycles in energy storage systems and environmental systems.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.20-20
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• 2007

Nanowire-based field-effect transistors (FETs) decorated with nanoparticles have been greatly paid attention as nonvolatile memory devices of next generation due to their excellent transportation ability of charge carriers in the channel and outstanding capability of charge trapping in the floating gate. In this work, top-gate single ZnO nanowire-based FETs with and without Au nanoparticles were fabricated and their memory effects were characterized. Using thermal evaporation and rapid thermal annealing processes, Au nanoparticles were formed on an $Al_2O_3$ layer which was semi cylindrically coated on a single ZnO nanowire. The family of $I_{DS}-V_{GS}$ curves for the double sweep of the gate voltage at $V_{DS}$ = 1 V was obtained. The device decorated with nanoparticles shows giant hysterisis loops with ${\Delta}V_{th}$ = 2 V, indicating a significant charge storage effect. Note that the hysterisis loops are clockwise which result from the tunneling of the charge carriers from the nanowire into the nanoparticles. On the other hand, the device without nanoparticles shows a negligible countclockwise hysterisis loop which reveals that the influence of oxide trap charges or mobile ions is negligible. Therefore, the charge storage effect mainly comes from the nanoparticles decorated on the nanowire, which obviously demonstrates that the top-gate single ZnO nanowire-based FETs decorated with Au nanoparticles are the good candidate for the application in the nonvolatile memory devices of next generation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.96-96
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• 2007

Low voltage organic TFTs (OTFTs) and ZnO based TFTs (<5V), utilizing room temperature deposited $Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7$ (BZN) thin films were recently reported, pointing to high-k gate insulators as a promising route for realizing low voltage operating flexible electronics. $Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7$ (BZN) thin film is one of the most promising materials for gate insulator because of its large dielectric constant (~60) at room temperature. However their tendency to suffer from relatively high leakage current at low electric field (>0.3MV/cm) hinder the application of BZN thin films for gate insulator. In order to improve leakage current characteristics of BZN thin film, we mixed 30mol% MgO with 70mol% BZN and their dielectric and electric properties were characterized. We fabricated field-effect transistors with transparent oxide semiconductor ZnO serving as the electron channel and high-k $(Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7)_{0.7}(MgO)_{0.3}$ as the gate insulator. The devices exhibited low operation voltages (<4V) due to high capacitance of the $(Bi_{1.5}Zn_{1.0}Nb_{1.5}O_7)_{0.7}(MgO)_{0.3}$ dielectric.

• JSTS:Journal of Semiconductor Technology and Science
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• v.11 no.3
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• pp.153-161
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• 2011

In this work, we report the physics-based SPICE model of amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) and demonstrate the SPICE simulation of amorphous InGaZnO (a-IGZO) TFT inverter by using Verilog-A. As key physical parameter, subgap density-of-states (DOS) is extracted and used for calculating the electric potential, carrier density, and mobility along the depth direction of active thin-film. It is confirmed that the proposed DOS-based SPICE model can successfully reproduce the voltage transfer characteristic of a-IGZO inverter as well as the measured I-V characteristics of a-IGZO TFTs within the average error of 6% at $V_{DD}$=20 V.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.25 no.3
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• pp.69-77
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• 2019

Agar-based nanocomposite films were prepared by incorporation of zinc oxide nanoparticles (ZnONP) and grapefruit seed extract (GSE). The composite films were characterized using FT-IR, UV-visible spectroscopy and thermalgravimetric analysis (TGA). The composite films showed light absorption peaks at 220 and 380 nm, characteristic for GSE and ZnONP, respectively. The UV-light transmittance of the agar film was markedly reduced from 54.4 ± 1.3% to 5.8 ± 2.5% with little sacrifice of transparency when 3 wt% ZnONP and 5 wt% GSE were added. The mechanical and water vapor barrier properties increased slightly though they were not significant statistically by the addition of ZnONP and GSE. The nanocomposite films showed stronger antibacterial activity against L. monocytogenes than E. coli O157: H7 and the antibacterial activity was affected by bacterial types as well as concentrations of ZnONP and GSE. The nano-composite film incorporated with 3 wt% of ZnONP and 5 wt% of GSE exhibited strong antibacterial activity against Listeria monocytogenes and E. coli O157: H7. The results indicate that 3 wt% of ZnONP and 5 wt% of GSE are the optimal concentrations for producing functional agar/ZnONP/GSE composite films.

• Journal of Energy Engineering
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• v.15 no.2 s.46
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• pp.107-117
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• 2006

The status of water splitting thermochemical cycle for hydrogen production was reviewed in this article. Mass production of hydrogen could be possible using the thermochemical process which is similar to the concept of conventional chemical reaction system if the high temperature heat source is available. The mediators (chemicals and reagents) should be used to split chemically stable water, and should be recycled in a closed cycle in order to be environmentally acceptable. Though there is no process to reach commercial stage, IS cycle, two-step cycles based on metallic oxide such as ZnO/Zn, $Fe_3O_4/FeO$ and the associated cycles are attracted due to their possibilities of application. Development of materials for high temperature and/or corrosive conditions during thermochemical process is still important topic in some thermochemical processes.

• ETRI Journal
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• v.31 no.6
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• pp.660-666
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• 2009

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top-gate In-Ga-Zn-oxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below $200^{\circ}C$, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as $Si_3N_4$ and $Al_2O_3$, the electrical properties are analyzed. After post-annealing at $200^{\circ}C$ for 1 hour in an $O_2$ ambient, the sub-threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative-bias stress tests on TFTs with a $Si_3N_4$ IDL, the degradation sources are closely related to unstable bond states, such as Si-based broken bonds and hydrogen-based bonds. From constant-current stress tests of $I_d$ = 3 ${\mu}A$, an IGZO-TFT with heat-treated $Si_3N_4$ IDL shows a good stability performance, which is attributed to the compensation effect of the original charge-injection and electron-trapping behavior.