Magnetoelectric multiferroics, where a ferromagnetic and a ferroelectric order coexist and are coupled in a single phase, have been a hot topic in condensed matter physics for a long time owing to their ability to facilitate nextgeneration applications. In this review, we briefly introduce basic concept of the magnetoelectric multiferroic oxides as well as their history, physical origins, and significant achievements. The key moments contributing to the progress of magnetoelectric multiferroics are snapshotted chronologically, and then a discussion on the major magnetic exchange interactions and the ferroelectric origins are presented along with their coupling behavior. Furthermore, we argue a need for modifying the present classification of magnetoelectric multiferroics before presenting the evolution of multiferroics using representative examples with their properties such as magnetic/ferroelectric transition temperature, magnetization/electric polarization, and magnetoelectric coefficient. We hope that this brief review will provide the community researchers with insights into magnetoelectric multiferroic oxides.

IEEE Standard on Piezoelectricity has been utilized for decades though it has shown significant issues that prevent researchers from obtaining accurate materials coefficients. To resolve these issues, our research group recently proposed partial electrode (PE) method. PE method utilizes samples that consist of the center part covered with electrode, and the side part either covered or not covered with electrode for obtaining both intensive and extensive elastic parameters. In this review, we introduce our PE method, along with physical phenomenology and background, such as issues of IEEE standard, to bolster readers understanding of needs for developing new measurement method that can compensate the standard method. It is shown that development of the PE method not only provides technological benefits, but also gives scientific importance for the piezoelectric research community from its extremely high data accuracy.

Inductively coupled plasma reactive ion etching (ICP-RIE) of copper thin films patterned with SiO₂ hard masks was carried out using piperidine/O₂/Ar gas mixture. The etch rate, etch selectivity, and etch profile of copper thin films were investigated by varying gas concentration in piperidine/O₂/Ar gas mixture. In addition, the etch parameters including ICP RF power, DC-bias voltage to substrate, and process pressure were varied to examine the etch characteristics. X-ray photoelectron spectroscopy and optical emission spectroscopy were employed to elucidate the etch mechanism under piperidine/O₂/Ar gas chemistry. Finally, 150 nm-line patterned copper thin films were successfully etched using piperidine/ O₂/Ar etch gas under the optimized etch conditions.

A machine vision inspection system consists of a camera, optics, illumination, and image acquisition system. The illumination system among these uses LED lighting source. Therefore, the driving method of LED lighting source is very important. The two main driving methods of LED lighting system for machine vision are Pulse Width Modulation (PWM) control driving and strobe control driving. PWM control driving method has problems such as a temperature rising of LED and a flickering in image measurement for inspection. On the other hand, strobe control driving method has a difficulty in the control of light intensity because of too short on-time. In this study, we propose a new hybrid-dimming control driving method for LED lighting source for machine vision. The proposed new hybrid-dimming control driving method can control current intensity and current on-time simultaneously so that it can extract clearer images with a high precision without the light saturation of image.

The transfer characteristics of amorphous indium gallium zinc oxide thin film transistor (a-IGZO TFT) showed the distortion in the subthreshold region after gate bias stress, in addition to the parallel shift of threshold voltage. The capacitancevoltage (C-V) curve was also deformed from its initial shape after the gate bias stress. This study analyzes both the C-V and transfer curves plotted on the same gate voltage axis in order to investigate the mechanism driving the distortion in the transfer curve. It is deduced that an additional interfacial trap states at the bottom interface of a-IGZO are produced during gate bias stress, thereby they exhibit the back channel effect, which explains the origin of the distortion in the transfer curve and the deformation of C-V curve.

In this study, solder joints mixed with graphene-nanosheets (GNSs) were investigated for the manufacture of highly reliable electronic devices. In order to analyze the effect of adding GNSs, experiments were performed by adding various amounts of GNSs (0.01, 0.05, 0.1, 0.3, 0.5 wt%). To compare and analyze the properties of the solder joints to which GNSs were added, shear forces were measured, and cross-sectional observation was performed. The bonding strength of the solder joints containing 0.05% GNSs was the highest, and the bonding strength of the solder joints with higher GNSs contents did not increase. This is because, as the content of GNSs increases, the viscosity of the solder paste also increases; therefore, the solder paste detachability from the metal mask was lowered and a sufficient amount was not applied. In addition, due to the high content of GNSs, the fluidity of solder powder and paste decreased, resulting in defects in the shape of the solder joint. Therefore, the optimal GNSs content in this study was 0.05%, and studies for optimal viscosity should be continued.

Durability of superconductors used to fabricate superconducting power machines is important, since the machines need to operate stably. Quench properties of GBCO (GdBa₂Cu₃O₇) coated conductor tapes laminated with brass were measured and analyzed to investigate the durability of tapes under repeated short-circuit conditions. With short currents applied to the tapes repeatedly, the quench properties of tapes were measured, and bubbles generated during quenches were observed. The results showed that quench resistance and distribution were maintained after repeated quenches. They were maintained after repeated quenches at various applied voltages, which show durability of the tapes under repeated short-circuit conditions. The quench distribution was uniform throughout repeated quenches, which contributed to the durability of tapes.

The 22.9 kV vacuum interrupter (VI) built-in load bus switcher (LBS), which is most often used as a load switch for distribution, extinguishes the arc that occurs during normal load opening and closing and fault current interruption within the VI housing to quickly switch circuits. As a protective device for contact separation, the rated current is supplied in a normal state. When a fault current flows due to a fault or an accident in the power system, the contact is disconnected in a vacuum state to block the fault current. In this study, in order to design the optimal VI, the heat dissipation characteristics of VI according to the center electrode distance 0/1/2/3 cm were analyzed by applying the finite element method, and the results were reflected to improve the structure of the VI.

We investigated deep levels in n-type 4H-SiC epitaxy layer of the Schottky barrier diodes (SBD) and Junction Barrier Schottky (JBS) diodes by using deep level transient spectroscopy (DLTS). The I-V characteristics of the JBS devices show ~100 times lower leakage current level than SBDs owing to the grid structures in JBS. The reliable responses of the diodes for deep level transient analysis showed from C-V characteristics. Several deep electron traps were revealed by DLTS measurements in epitaxial layers in 4H-SiC. In both types of diodes, the peaks corresponding to shallow energy levels were observed with slightly different values of 0.132 eV for JBS and 0.186 eV for SBDs. The two remarkable deep level peaks (J2 and J3) have been obtained with 0.257 eV and 0.273 eV in JBS, and they were analyzed to have a similar trap concentration of ~10¹⁴ cm^-3. The comparison results showed that the defects could be related with device fabrication procedures such as ion-implantation and growth.