• Electronics and Telecommunications Trends
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• v.34 no.5
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• pp.71-80
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• 2019

Gallium nitride (GaN) can be used in high-voltage, high-power-density/-power, and high-speed devices owing to its characteristics of wide bandgap, high carrier concentration, and high electron mobility/saturation velocity. In this study, we investigate the technology trends for X-/Ku-band GaN RF power devices and MMIC power amplifiers, focusing on gate-length scaling, channel structure, and power density for GaN RF power devices and output power level and output power density for GaN MMIC power amplifiers. Additionally, we review the technology trends in gallium arsenide (GaAs) RF power devices and MMIC power amplifiers and analyze the technology trends in RF power devices and MMIC power amplifiers based on both GaAs and GaN. Furthermore, we discuss the current direction of national research by examining the national and international technology trends with respect to X-/Ku-band power devices and MMIC power amplifiers.

• Journal of IKEEE
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• v.23 no.1
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• pp.326-329
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• 2019

Gallium nitride(GaN) has been a superior candidate for the next generation power electronics. As GaN-on-Si substrate technology is mature, there has been new demand for monolithic integration of GaN technology with Si CMOS devices. In this work, (110)Si CMOS process was developed and the fabricated devices were evaluated in order to confirm the feasibility of utilizing domestic foundry facility for monolithic integration of Si CMOS and GaN power devices.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.9-15
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• 2018

This paper shows the principles and characteristics of the transient liquid phase (TLP) bonding technology for power modules packaging. The power module is semiconductor parts that change and manage power entering electronic devices, and demand is increasing due to the advent of the fourth industrial revolution. Higher operation temperatures and increasing current density are important for the performance of power modules. Conventional power modules using Si chip have reached the limit of theoretical performance development. In addition, their efficiency is reduced at high temperature because of the low properties of Si. Therefore, Si is changed to silicon carbide (SiC) and gallium nitride (GaN). Various methods of bonding have been studied, like Ag sintering and Sn-Au solder, to keep up with the development of chips, one of which is TLP bonding. TLP bonding has the advantages in price and junction temperature over other technologies. In this paper, TLP bonding using various materials and methods is introduced. In addition, new TLP technologies that are combined with other technologies such as metal powder mixing and ultrasonic technology are also reviewed.

• Journal of Powder Materials
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• v.28 no.2
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• pp.150-163
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• 2021

Interest in eco-friendly materials with high efficiencies is increasing significantly as science and technology undergo a paradigm shift toward environment-friendly and sustainable development. MXenes, a class of two-dimensional inorganic compounds, are generally defined as transition metal carbides or nitrides composed of few-atoms-thick layers with functional groups. Recently MXenes, because of their desirable electrical, thermal, and mechanical properties that emerge from conductive layered structures with tunable surface terminations, have garnered significant attention as promising candidates for energy storage applications (e.g., supercapacitors and electrode materials for Li-ion batteries), water purification, and gas sensors. In this review, we introduce MXenes and describe their properties and research trends by classifying them into two main categories: transition metal carbides and nitrides, including Ti-based MXenes, Mo-based MXenes, and Nb-based MXenes.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.23-31
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• 2021

Surface texturing is a promising route to reduce the friction forces between two surfaces in sliding contact. To this end, the fabrication of micro dimples is one of the most widely used surface texturing methods. According to published results, textured surfaces with elliptical micro dimples offer the best friction performance. Therefore, we fabricated elliptical micro dimples on carbon steel (SM45C) by using dual frequency vibration assisted machining. High and low frequencies of 16.3 kHz and 230 Hz were applied to the 3D resonant elliptical vibrator. The 3D resonant elliptical vibrator with a triangular cubic boron nitride insert was assembled on a computer numerically controlled turning lathe. Oval micro dimples of various profiles were manufactured on carbon steel. In terms of the profile of the elliptical micro dimples, the experimental results indicated that the average micro dimple width and depth were 112 ㎛ and 7.7 ㎛. These dimensions are closely related to the cutting conditions and can be easily controlled.

• Korean Journal of Metals and Materials
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• v.46 no.11
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• pp.708-712
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• 2008

The influence of high temperature gas nitriding (HTGN) in STS347 and STS310S steels was experimentally investigated. The HTGN was carried out at $1,050^{\circ}C{\sim}1,150^{\circ}C$ for 10 hrs in a gaseous atmosphere containing $1kg/mm^2$ of nitrogen. After HTGN, fine precipitates of $Cr_2N$ and NbN appeared in austenite on the surface of STS 347, while nitrogen pearlite, which was layeredof $Cr_2N$ and austenite alternatively, appeared in austenite on the surface of STS 310S. The surface hardness of HTGN-treated, STS 347 and STS 310S specimens was 250~360 Hv and 270~400 Hv, respectively, depending on the temperature of HTGN. The nitrogen content was analyzed 1.4 wt% and 1.6 wt% at the surface layer of STS 347 and STS 310S steels, respectively. In addition, an improvement in the corrosion resistance of HTGN treated specimens was observed.

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.722-727
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• 2009

The bipolar plates are not only the major part of the polymer electrolyte membrane fuel cell (PEMFC) stack in weight and volume, but also a significant contributor to the stack costs. Stainless steels are considered to be good candidates for bipolar plate materials of the PEMFC due to their low cost, high strength and easy machining, as well as corrosion resistance. In this paper, 316L stainless steel with and without nitrogen ion implantation were tested in simulated PEMFC environments for application as bipolar plates. The results showed that the nitride formed by nitrogen ion implantation contributed the decrease of the interfacial contact resistance without degradation of corrosion property. The combination of excellent properties indicated that nitrogen ion implanted stainless steel could be potential candidate materials as bipolar plates in PEMFC. Current efforts have focused on optimizing the condition of ion implantation.

• Korean Journal of Metals and Materials
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• v.49 no.3
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• pp.203-210
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• 2011

Bake hardening steels have to resist strain aging to prevent the yield strength increment and stretcher strain during press process and to enhance the bake hardenability during baking process after painting. The bake hardening steels need to control the solute carbon and the solute nitrogen to improve the bake hardenability. Ti and/or Nb alloying for nitride and carbide precipitation and low carbon content below 0.003% are used to solve strain aging and formability problem for automotive materials. However, in the present study, the effect of micro-precipitation of copper sulfide on the bake hardenability and fatigue properties of extremely low carbon steel has been investigated. The bake hardenability of Cu-alloyed bake hardening (Cu-BH) steel was slightly higher (5 MPa) than that of Nb-alloyed bake hardening (Nb-BH) steel, but the fatigue limit of Cu-BH steel was far higher (45 MPa) than that of Nb-BH steel. All samples showed the ductile fracture behavior and some samples revealed distinct fatigue stages, such as crack initiation, stable crack growth and unstable crack growth.

• Journal of the Korean institute of surface engineering
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• v.54 no.3
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• pp.139-143
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• 2021

Cr-Al-N coatings were deposited onto WC-Co substrates using a cathodic arc evaporation (CAE) system. CAE technique is recognized to be a very useful process for hard coatings because it has many advantages such as high packing density and good adhesion to metallic substrates. In this study, the influence of deposition temperature as a key process parameter on film growth behavior and mechanical properties of Cr-Al-N coatings were systematically investigated and correlated with microstructural changes. From various analyses, the Cr-Al-N coatings prepared at deposition temperature of 450℃ in the CAE process showed excellent mechanical properties with higher deposition rate. The Cr-Al-N coatings with deposition temperature around 450℃ exhibited the highest hardness of about 35 GPa and elastic modulus of 442 GPa. The resistance to elastic strain to failure (H/E ratio) and the index of plastic deformation (H³/E² ratio) were also good values of 0.079 and 0.221 GPa, respectively, at the deposition temperature of 450℃. Based on the XRD, SEM and TEM analyses, the Cr-Al-N coatings exhibited a dense columnar structure with f.c.c. (Cr,Al)N multi-oriented phases in which crystallites showed irregular shapes (50~100nm in size) with many edge dislocations and lattice mismatches.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.1
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• pp.13-20
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• 2021

GaN has shown good potential owing to its better chemical stability than other materials and tunable bandgap with materials such as InN and AlN. Tunable bandgap allows GaN to make the maximum utilization of the solar spectrum, thus improves the solar-to-hydrogen (STH) efficiency. In addition, GaN band gap contains the oxidation and reduction level of water, so it can split water without external voltage. However, STH efficiency using GaN itself is low and has been actively studied recently to improve it. In this thesis, we have summarized the studies related to the use of GaN as a photoelectrode for photoelectrochemical water splitting.