We have studied the thermal stability of NCM622 cathode material for Li-ion batteries using real-time synchrotron x-ray scattering below 600°C in both air and vacuum. The expansion of the mean particle size, which reached maximum values of 10.3 μm in air and 10.6 μm in vacuum at 200°C, was attributed to the dehydration of intergranular water within the NCM622 powders. Across all annealing temperatures, the amount of crystal NCM622 phase in air was consistently higher than that in vacuum. The crystal domain sizes in air showed less variation than that in vacuum during annealing from RT to 500°C. These indicate that the crystal NCM622 phase is more thermally stable during annealing in air than in vacuum. This stability is attributed to the presence of 21% oxygen in air, which is absent under vacuum conditions.

Dye adsorption is one of the most time-consuming processes in the fabrication of dye-sensitized solar cells (DSSCs), typically requiring approximately 24 h at room temperature. In this study, the effect of adsorption temperature and time on photovoltaic performance of DSSCs was investigated in order to reduce processing time and improve device productivity. Nanoporous TiO₂ photoelectrodes were immersed in N719 dye solution at 60°C for 3 h, 10 h, 17 h, and 24 h, and their performance was compared with that of cells sensitized at room temperature for 24 h. Photovoltaic characterization under AM 1.5 illumination showed that DSSCs sensitized at 60°C exhibited improved performance compared to those sensitized at room temperature. The device sensitized at 60°C for 3 h showed comparable or higher conversion efficiency than the reference cell sensitized for 24 h at room temperature. The improvement in device performance is attributed to enhanced dye adsorption kinetics resulting from increased reaction rate between the carboxyl groups of N719 dye molecules and hydroxyl groups on the TiO₂ surface. Electrochemical impedance spectroscopy analysis revealed reduced recombination resistance at the TiO₂/dye/electrolyte interface for cells sensitized at elevated temperature. UV–Vis absorption analysis confirmed increased dye loading on the TiO₂ surface for the 60°C condition. These results demonstrate that elevated temperature dye adsorption significantly reduces processing time while maintaining photovoltaic performance, providing an effective strategy for improving manufacturing efficiency of DSSCs.

The potential of replacing crosslinked polyethylene (XLPE) with an eco-friendly alternative, polypropylene (PP), as insulating material is investigated for overhead power distribution lines. Although XLPE exhibits excellent electrical and mechanical properties, the byproducts generated during crosslinking pose environmental challenges. PP is a viable alternative because of recyclability and absence of byproducts during crosslinking. This study evaluated alternating current (AC) breakdown strength, contact angle, and tracking resistance of two commercially available XLPE samples and three types of PP (PP1, PP2, PP3) with varying additive content. AC breakdown strength, analyzed using the Weibull distribution, facilitated relative comparison of insulation performance. PP2 exhibited scale parameters comparable to or exceeding those of XLPE. Contact angles exceeding 90° displayed hydrophobicity across all samples. To address pass/fail evaluation limitations, arcing images from tracking tests were analyzed using the box-counting method for fractal dimension analysis. Fractal dimensions increased with arcing extent, and complexity increased with test duration. Tracking resistance performance order was PP3, PP1, CC, PP2, OC which was attributed to enhanced heat dissipation properties of filler additives. The proposed quantitative method for comparing tracking resistance through fractal dimension analysis, explored the feasibility of using PP insulating materials in overhead power distribution lines.

The safety and stability concerns of liquid electrolytes in conventional lithium-ion batteries have accelerated the development of solid-state alternatives. NASICON type ceramics Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) offer promising properties, including high bulk ionic conductivity and good compatibility with lithium anodes. However, their practical application is hindered by grain boundary resistance and relatively low total ionic conductivity. This study investigates the effect of Ta₂O₅ doping on LATP to overcome these limitations. Doping with 5 wt% Ta₂O₅ improved the ionic conductivity to 2.95 × 10-4 S/cm by enhancing lattice structure, reducing grain boundary resistance, and suppressing the formation of secondary phase. Additionally, Ta₂O₅ positively influenced the sintering behavior, resulting in a denser, and more uniform microstructure. These enhancements suggest that Ta₂O₅-doped LATP is a strong candidate for next-generation all-solid-state lithium-ion batteries.

Bismuth layer-structured ferroelectrics with high Curie temperatures have recently attracted significant attention as promising candidates for high-temperature piezoelectric applications. However, the conventional solid-state reaction method entails high-temperature processing that induces bismuth volatilization, thereby degrading device reliability. In this study, we employed a co-precipitation method enabling atomic-level mixing to significantly lower the synthesis temperature of Nb/Tadoped Bi₄Ti₃O₁₂ ceramics compared to the solid-state reaction method. Experimental results demonstrated that the coprecipitation method yielded a pure single phase at 600℃ without intermediate phases. Furthermore, the synthesized nanopowders, with an average size of 100 nm, lowered the onset temperature of sintering shrinkage to 650℃, approximately 200℃ lower than that of the solid-state counterpart. The low-temperature synthesis process proposed in this work is expected to contribute to the performance enhancement of high-temperature piezoelectric devices by effectively suppressing bismuth volatilization and ensuring compositional stability.

AlGaN/GaN High Electron Mobility Transistors (HEMTs) are emerging as next-generation semiconductors optimized for high-power and high-frequency applications, with their performance highly dependent on the surface and interface quality of the AlGaN/GaN structure. In particular, the 2-Dimensional Electron Gas (2DEG) formed in the AlGaN layer is susceptible to trapping by surface defects, which degrades electrical characteristics and makes the device vulnerable to degradation. In this study, we propose an approach to enhance device reliability and performance by forming a gallium oxynitride (GaON) interfacial layer through O₂ plasma treatment on the AlGaN surface. This method effectively suppresses interface defects, resulting in improved electrical properties such as reduced interface trap density (Dit), threshold voltage (Vth) shift, increased drain current density (Id), and enhanced transconductance density (gm). Furthermore, this surface treatment demonstrates the potential for process simplification by improving the electrical characteristics of power semiconductor devices without the need for complex deposition steps.

Multilayer ceramic capacitors (MLCCs) are essential for high-capacitance, miniaturized, and reliable electronic applications. This study examines the impact of layer stacking on the dielectric and electrical properties of MLCCs using a BaTiO₃-based dielectric with MgO, Mn₃O₄, Yb₂O₃, V₂O₅, and (BaCa)SiO₃ glass additives. MLCCs with 10 um-thick dielectric layers and varying Ni electrode layers (10, 30, 50, and 100 layers) were fabricated. The dielectric constant increases significantly up to 30 layers due to compressive stress and sintering densification but it becomes linear beyond 30 layers. Dissipation factor and ESR decrease with higher stacking due to improved sinterability, while breakdown voltage declines exponentially from defect accumulation and thermal stress. Insulation resistance decreases but stabilizes relative to capacitance. C-V results show stress-induced polarization suppression, which reduces the dielectric constant under high voltage. Optimized stacking and sintering conditions are crucial for MIL-PRF-32535 compliant MLCC designs.

This study developed a dielectric composition for high-capacitance MLCCs with C0G and U2J temperature compensation characteristics (Class I) under reducing conditions. The potential application of this composition in highpermittivity class I MLCCs was examined. Using (Ba₀.₂₄Ca₀.₁₆Sr₀.₆)(TiₓZr₁₋ₓ)O₃. XRD analysis showed that secondary phases like Sr₂TiO₄ and TiO₂ formed at higher Ti content, affecting the stoichiometric balance. Adjusting the Ti/Zr molar ratio resulted in a dielectric constant of 41.2 ~ 105, a dielectric loss of 0.082 ~ 0.174%, and insulation resistance above 1.6 × 10¹³ ohms at 25℃. The TCC shifted from C0G to U2J as the Ti/Zr ratio increased, but the composition enabled the design of high-capacitance and high-voltage MLCCs with favorable dielectric and electrical properties.

The continuous and long-lasting monitoring of physiological signals induced from the human body is crucial for health monitoring, disease diagnosis, and treatment. In this study, we have reported the Seebeck effect-based flexible selfpowered temperature sensor which can convert the electric signals from lateral temperature difference. For demonstrating temperature sensor arrays, the p-type thermoelectric (TE) composite films were fabricated by dispersing the Bi_0.5Sb_1.5Te₃ (BST) powders inside poly-vinylidene fluoride matrix and subsequently attached to the patterned electrode foils. The inorganic BST powders-embedded TE composite films with activated area of 0.5 × 1 cm² harvest a maximum voltage of 1.7 mV, a maximum current of 5.6 mA, and an output power of 2.6 nW from the temperature gradient (ΔT) of 20 K. Finally, the fabricated selfpowered temperature sensor array well detected the pattern images of external thermal source of ΔT = 20 K. This study manifests flexible temperature sensor array which paves the way for further advancements in this field.

In parallel with the efforts to improve the device performance in modern integrated circuits, it is necessary to downscale their core components, field-effect transistors (FETs), generally gauged by their physical gate length. Upon such device scaling, the emergence of the short-channel effect impedes further scaling into the nanometer scale in the silicon VLSI (Very-Large-Scale-Integration) system. To address this issue, two-dimensional (2D) semiconductors, leveraging their atomically thin thickness and dangling-bond-free characteristics, are being highlighted as a material solution for future scaling technology without severe mobility degradation. Despite the expected ideal physical properties, 2D semiconductors have yet to realize their full potential owing to the limited development of integration technology. In this context, we survey and review the tailored van der Waals integration technologies for 2D FETs. In particular, we provide an in-depth study of both van der Waals integrated contact and dielectric methods along with an explanation of customized materials. In essence, this van der Waals integrationcentered approach will be a core strategy to implement the high-performance 2D transistors that meet the demand of FET miniaturization.

Piezoelectric materials, which convert mechanical energy into electrical signals, are widely used in various industrial applications such as sensors, actuators, and energy harvesting devices. This study aims to enhance the performance of Pb(Mg_1/3Nb_2/3)O₃-Pb(Al_1/2Nb_1/2)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PAN-PZT) piezoelectric ceramics by investigating the effects of varying PAN and PMN content and adding Nb₂O₅ on their piezoelectric properties. The results show that with 2 mol% of PMN and PAN, the morphotropic phase boundary (MPB) region exhibits the highest piezoelectric properties. Additionally, excess Nb₂O₅ positively influenced the piezoelectric properties, maximizing electro-mechanical coupling factor (k_p=63%, d₃₃=440 pC/N). These findings contribute to developing next-generation high-performance piezoelectric materials, with potential for improved efficiency and performance in various industries.

Perovskite, which follows the chemical formula ABX3 and exhibits an octahedral structure, is primarily a hybrid of organic and inorganic materials. It can be broadly categorized into three types based on dimensionality: 0D nanocrystals, quasi- 2D, and 3D bulk structures. As a result, it is gaining attention as a next-generation optoelectronic material for applications in light-emitting devices, solar cells, and sensors. This paper provides insights into dimension of perovskites, their respective synthesis methods, and current research trends, thereby offering prospects for advancements in the study of next-generation optoelectronic materials.

In this study, the effect of thickness on the Sn-doped β-Ga₂O₃ thin films was investigated. β-Ga₂O₃ is a next-generation material for power semiconductors and optoelectronics owing to its remarkable properties, such as an ultra-wide bandgap, excellent thermal and chemical stability, and large breakdown voltage. However, its inherently low conductivity can be limiting in applications that require high conductivity; therefore, improving the conductivity of β-Ga₂O₃ is important. In this study, Sn-doped β-Ga₂O₃ thin films with various thicknesses were deposited on β-Ga₂O₃ substrates. All the fabricated samples exhibited β-phase with a uniform and dense surface and transmittance of above 80% in the visible region. In particular, the 100 nm samples showed the highest carrier concentration and mobility and the lowest resistivity. Thus, these findings are expected to play an important role in improving the performance of devices by controlling the thickness of thin films.

Cu₂O metal oxide was synthesized using NaBH₄ as a reducing agent in this study. The transformation of Cu composite with the pH adjustment was investigated, and the conditions for Cu₂O synthesis were analyzed. As pH of the solution was changed, the synthesized Cu composite evolved into Cu/Cu₂O and Cu/Cu₂O/CuO composites. The Cu₂O composite synthesized under conditions closest to pure Cu₂O was heat-treated at 200℃. The remaining minor Cu metal was oxidized, resulting in pure Cu₂O particles with enhanced crystallinity. The synthesized Cu₂O exhibited various morphology with particle sizes of about 160~720 nm, and the shape and size of the Cu₂O particles remained significantly unchanged after heat treatment. Surface analysis was conducted to compare the changes before and after heat treatment. No significant changes were observed, except for those attributed to water evaporation. The Cu₂O synthesized via this simple chemical reduction method can be utilized in various application fields, including catalysts, optical devices, and sensors.

This study investigates the effects of chemical etching for anti-glare (AG) treatment and the subsequent deposition of a TiZrO₂/SiO₂ double-layer anti-reflection (AR) coating on glass surfaces. The AG treatment was performed using ammonium fluoride in gel form via screen printing, followed by electron beam deposition of SiO₂/TiZrO₂ layers. The surface roughness, optical transmittance, and refractive index were analyzed. The results revealed that while the surface roughness increased with larger screen patterns during the AG treatment, it was reduced by the deposition of the AR layers. Additionally, the gloss caused by external light was higher with lower surface roughness, but it was effectively reduced by the AR coating. The optical reflectance showed minimal changes during the AG treatment, remaining similar to that of bare glass substrates. However, the AR coating significantly decreased reflectance. The combination of AG treatment and AR coating improved optical transmittance and reduced gloss, making this method beneficial for enhancing visibility in automotive displays. The findings suggest that this approach can mitigate the impact of external light and improve the clarity of displayed information, making it suitable for automotive display applications.

Memristors, as next-generation memory devices, have garnered significant academic interest. Among them, TiO₂/TiO_2-x based memristors have particularly attracted substantial scholarly attention. Research on the activation and stability of TiO2 based memristor devices through process parameters is essential. Here, to determine the impact of process parameters on the activation of TiO₂/TiO_2-x based memristor devices, we fabricated the memristor devices using a sputtering system andconducted annealing at 400℃. Additionally, to analyze the electrical characteristics of the devices, we measured the I-V curves and C-V curves. Also, we examined TiO₂/TiO_2-x based memristor devices surface using SEM. Consequently, it was observed that the devices subjected to annealing exhibited improved hysteresis curves in the I-V characteristics, a reduced bandgap, and changes in resistance compared to the non-annealed devices. The retention test results further demonstrated that the set/reset characteristics of the devices were stable, confirming their potential applicability as memory devices.

In this study, we fabricated single grain YBCO bulk superconductors with control of the distance between the seed and the upper surface of the YBCO compacts. The magnetic levitation force of the YBa₂Cu₃O₇ superconducting bulk, which corresponds to the energy amount of the superconducting bulk, was measured to be 32.634 N at the center of the bulk where the seed was placed. Under field cooling conditions, a capture magnetic force of 2.17 kG was observed at the center of the bulk. The trapped magnetic force curve corresponding to the stability of the superconducting bulk means that the superconducting specimens were well grown in the form of single grains.

The key to determining the lifetime of OLED device is how much brightness can be maintained. It can be said that there are internal and external causes for the degradation of OLED devices. The most important cause of internal degradation is bonding and degradation in the excited state due to the electrochemical instability of organic materials. The structure of OLED modeled in this paper consists of a cathode layer, electron injection layer (EIL), electron transport layer (ETL), light emission layer, hole transport layer (HTL), hole injection layer (HIL), and anode layer on a glass substrate from top to bottom. It was confirmed that the temperature generated in OLED was distributed around the maximum of 343.15 K centered on the emission layer. It can be seen that the heat distribution generated in the presented OLED structure has an asymmetrically high temperature distribution toward the cathode, which is believed to be because the sizes of the cathode and positive electrode are asymmetric. Therefore, when designing OLED, it is believed that designing the structures of the cathode and anode electrodes as symmetrically as possible can ensure uniform heat distribution, maintain uniform luminance of OLED, and extend the lifetime. The thermal distribution of OLED was analyzed using the finite element method according to Comsol 5.2.

This reports the electrical properties of single-crystal β-gallium oxide (β-Ga₂O₃) vertical Schottky barrier diodes (SBDs) with a different guard ring structure. The vertical Schottky barrier diodes (V-SBDs) were fabricated with two types guard ring structures, one is with metal deposited on the Al₂O₃ passivation layer (film guard ring: FGR) and the other is with vias formed in the Al₂O₃ passivation layer to allow the metal to contact the Ga₂O₃ surface (metal guard ring: MGR). The forward current values of FGR and MGR V-SBD are 955 mA and 666 mA at 9 V, respectively, and the specific on-resistance (Ron,sp) is 5.9 mΩ·cm² and 29 mΩ·cm². The series resistance (Rs) in the nonlinear section extracted using Cheung’s formula was 6 Ω, 4.8 Ω for FGR V-SBD, 10.7 Ω, 6.7 Ω for MGR V-SBD, respectively, and the breakdown voltage was 528 V for FGR V-SBD and 358 V for MGR V-SBD. Degradation of electrical characteristics of the MGR V-SBD can be attributed to the increased reverse leakage current caused by the guard ring structure, and it is expected that the electrical performance can be improved by preventing premature leakage current when an appropriate reverse voltage is applied to the guard ring area. On the other hand, FGR V-SBD shows overall better electrical properties than MGR V-SBD because Al₂O₃ was widely deposited on the Ga₂O₃ surface, which prevent leakage current on the Ga₂O₃ surface.

This study examines a manufacturing process for the photoelectrode material of dye-sensitized solar cell (DSSC) intending to increase efficiency through the surface plasmon resonance phenomenon of nanoparticles with a composite structure made of Ag and TiO₂. This invention involves the use of Ag and TiO₂ nanoparticles in the solar cell. These nanoparticles cause surface plasmon resonance, which amplifies and scatters incident solar energy, enhancing the dye’s rate of light absorption. It also makes it possible to absorb energy in wavelength ranges that were previously difficult to do, which increases efficiency. Centrifugal separation and heat synthesis are used to create the composite metal structures, and certain combinations are used to decide the particle morphologies. To increase the efficiency of organic solar cells and DSSC, the Ag/TiO₂ composite structure is therefore quite likely to be used.

This paper introduces an optimized oxygen (O₂) plasma surface treatment technique to enhance sphere lithography on hydrophobic photoresist surfaces. The focus is on semiconductor manufacturing, particularly the creation of finer structures beyond the capabilities of traditional photolithography. The key breakthrough is a method that makes substrate surfaces hydrophilic without altering photoresist patterns. This is achieved by meticulously controlling the O₂ plasma treatment duration. The result is the consistent formation of nano and microscale patterns across large areas. From an academic perspective, the study deepens our understanding of surface treatments in pattern formation. Industrially, it heralds significant progress in semiconductor and precision manufacturing sectors, promising enhanced capabilities and efficiency.

In this study, we successfully synthesized copper oxide (Cu₂O) particles through a hydrothermal method at a relatively low temperature (150℃). The synthesis involved the precise control of molar concentrations of NaOH. Notably, Cu₂O particles were effectively synthesized when NaOH concentrations of 0.15 M and 0.20 M were utilized. While attempts were made at different molar concentrations, the synthesis of pure Cu₂O particles was only achieved at concentrations of 0.15 M and 0.20 M. In this experimental investigation, Cu₂O synthesized under these specific conditions exhibited absorption characteristics within the wavelength range of 640 to 570 nm, consistently exhibiting a band gap energy of 1.9 eV. These Cu₂O particles, characterized by their small band gap energy and straightforward synthetic method, hold significant promise for various applications including semiconductors and solar cells.

To evaluate the possibility as a multi-level memory medium for the Ge2Sb2Te5/TiN/W-doped Ge2Sb2Te5 cell structure, the crystallization rate and stabilization characteristics according to voltage (V)- and current (I)- pulse sweeping were investigated. In the cell structures prepared by a magnetron sputtering system on a p-type Si (100) substrate, the Ge2Sb2Te5 and W-doped Ge2Sb2Te5 thin films were separated by a barrier metal, TiN, and the individual thicknesses were varied, but the total thickness was fixed at 200 nm. All cell structures exhibited relatively stable multi-level states of high-middle-low resistance (HR-MR-LR), which guarantee the reliability of the multilevel phase-change random access memory (PRAM). The amorphousto- multilevel crystallization rate was evaluated from a graph of resistance (R) vs. pulse duration (T) obtained by the nanoscaled pulse sweeping at a fixed applied voltage (12 V). For all structures, the phase-change rates of HR→MR and MR→LR were estimated to be approximately t<20 ns and t<40 ns, respectively, and the states were relatively stable. We believe that the doublestack structure of an appropriate Ge-Sb-Te film separated by barrier metal (TiN) can be optimized for high-speed and stable multilevel PRAM.

We have studied the effects of Ag on the characteristics of Sn₄₈In₅₂Ag_x (wt%) low-melting solders for photovoltaic ribbons. The Sn₄₈In₅₂ (wt%) solder coexisted in the InSn₄ and In₃Sn alloys. Ag atoms added in the solder formed an AgIn₂ alloy by reacting with some part of In atoms, while they did not react with Sn atoms. The addition of Ag atoms in the Sn₄₈In52Agx (wt%) solders showed useful results; an increase in peel strength and a decrease in melting temperature. The peel strength of the ribbon plated with the Sn⁴⁸In⁵² (wt%) solder was 53.6 N/mm², and that of the Sn⁴⁸In⁵²Ag1 (wt%) solder largely increased to 125.1 N/mm². In the meanwhile, the melting temperature of the Sn₄₈In⁵² (wt%) solder was 119.2℃, and that of the Sn48In52Ag1 (wt%) solder decreased to 114.0℃.

The Ga₂O₃ thin films were deposited using an RF sputtering system and the effect of crystallographic and optical properties under rapid thermal annealing conditions on Ga₂O₃ thin film was evaluated. A rapid thermal annealing method can fabricate a crystalline Ga₂O₃ thin film which is applied to various fields with a low cost and a high efficiency compared with the conventional post-annealing method. In this study, the Ga₂O₃ treated at 900℃ for 1 min showed the beta and gamma phases in XRD measurement. In optical properties, the crystalline Ga₂O₃ represented a high transmittance of more than 80% in the visible region and was calculated with a high optical bandgap energy of 4.58 eV. The beta and gamma phases Ga₂O₃ can be obtained by adjusting the rapid thermal annealing temperatures, and the various properties such as the optical bandgap energy can be controlled. Moreover, it is expected that crystalline Ga₂O₃ can be applied to various devices by controlling not only temperature but process time.

Recently, with the development of the smart device market, the integration of high-functional devices has increased the heat density, causing overload of the device, and resulting in various problems such as shortened lifespan, performance degradation, and failure. Therefore, research on heat dissipation materials is being actively conducted to realize next-generation electronic products. The heat dissipation material is characterized in that it is easy to dissipate heat due to its high thermal conductivity and minimizes leakage current flowing through the heat dissipation material due to its low electrical conductivity. In this study, flower-shaped Al₂O₃ and BN composites were engineered with a simple hydrothermal synthesis approach, and their thermal conductivity characteristics were compared and evaluated for each synthesis condition for the application to a heat dissipation material. Spherical BN and flower-shaped Al₂O₃ were easily obtained, and SEM/EDS analyses confirmed the uniform presence of BN between the Al₂O₃, and it can be expected that these shapes can affect the thermal conductivity.

Lithium-ion batteries are widely used in various applications, including electric vehicles and portable electronics, due to their high energy density and long cycle life. The performance of lithium-ion batteries can be improved by using solid electrolytes, in terms of higher safety, stability, and energy density. Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is a promising solid electrolyte for all-solid-state lithium batteries due to its high ionic conductivity and excellent stability. However, the ionic conductivity of LATP needs to be improved for commercializing all-solid-state lithium battery systems. In this study, we investigate the microstructures and ionic conductivities of LATP by incorporating B₂O₃ glass ceramics. The smaller grain size and narrow size distribution were obtained after the introduction of B₂O₃ in LATP, which is attributed to the B₂O₃ glass on grain boundaries of LATP. Moreover, higher ionic conductivity can be obtained after B₂O₃ incorporation, where the optimal composition is 0.1 wt% B₂O₃ incorporated LATP and the ionic conductivity reaches 8.8×10^-5 S/cm, more than 3 times higher value than pristine LATP. More research could be followed for having higher ionic conductivity and density by optimizing the processing conditions. This facile approach for establishing higher ionic conductivity in LATP solid electrolytes could accelerate the commercialization of all-solid-state lithium batteries.

The effect of sputtering power on the amorphous Ga₂O₃ thin film deposited using the radio frequency sputtering system was evaluated. Amorphous Ga₂O₃ is cheaper and more efficiently fabricated than crystalline Ga₂O₃, and is studied in various fields such as RRAM, photodetector, and flexible devices. In this study, amorphous Ga₂O₃ was deposited by radio frequency sputtering system and represented a transmittance of over 80% in the visible light region and a homogeneous and dense surface. The optical band gap energy decreased as the sputtering power increased owing to the quantum size effect. Thus, the specific band gap of amorphous Ga₂O₃ can be obtained by adjusting the sputtering power, it indicates amorphous Ga₂O₃ can be used in various fields.

It was reported that a tetragonal phase can be stabilized with maintaining good piezoelectric properties when Na_0.5K_0.5NbO₃ (KNN) is modified with 0.06 mol SrTiO₃. However, such a high amount of SrTiO₃ leads not only to poor sinterability but low Curie temperature (TC). To maintain high TC with good piezoelectric properties in KNN-based lead-free piezoelectric ceramics, this study investigates the effect of Li-doping on the dielectric and piezoelectric properties of 0.96Na_0.5K_0.5NbO₃-0.04SrTiO₃ (KNN-4ST) ceramics. As a result, the orthorhombic-tetragonal phase transition was observed at 2 mol% Li₂CO₃ modified KNN-4ST ceramics, whose TC, d33 and kp values are 328℃, 165pC/N and 0.33, respectively.

In this study, the heteroepitaxial thin film growth of β-Ga₂O₃ was studied according to the position of the susceptor in mist-CVD. The position of the susceptor and substrate was moved step by step from the center of the hot zone to the inlet of mist in the range of 0~50 mm. It was confirmed that the average thickness increased to 292 nm (D1), 521 nm (D2), and 580 nm (D3) as the position of the susceptor moved away from the center of the hot zone region. The thickness of the lower region of the substrate is increased compared to the upper region. The surface roughness of the lower region of the substrate also increased because the nucleation density increased due to the increase in the lifetime of the mist droplets and the increased mist density. Therefore, thin film growth of β-Ga₂O₃ in mist-CVD is performed by appropriately adjusting the position of the susceptor (or substrate) in consideration of the mist velocity, evaporation amount, and temperature difference with the substrate, thereby determining the crystallinity of the thin film, the thickness distribution, and the thickness of the thin film. Therefore, these results can provide insights for optimizing the mist-CVD process and producing high-quality β-Ga₂O₃ thin films for various optical and electronic applications.