Conductive inks are essential for developing flexible and wearable electronic devices, where printability and electrical performance must be finely balanced. However, achieving high conductivity while minimizing costly silver filler content remains a key challenge in ink formulation. In this work, we demonstrate that a simple ball-milling process transforms spherical silver particles into platelet-shaped fillers, dramatically enhancing conductivity at equivalent filler loading. The resulting inks show a reduction in sheet resistance from ~180 Ω/□ to ~ 0.57 Ω/□ at 70 wt% filler content, with improved performance attributed to surface-to-surface contact between platelets. Moreover, we show that filler content influences not only electrical conductivity but also ink viscosity, with the 53.8 wt% formulation achieving a practical balance between conductivity, processability, and cost. This morphology- and composition-controlled ink design offers a scalable strategy for manufacturing high-performance, cost-effective conductive inks suitable for next-generation printed electronics.

In this study, we fabricated a metamorphic high-electron-mobility transistor (mHEMT) device with a T-type gate structure for the implementation of W-band monolithic microwave integrated circuits (MMICs) and investigated its characteristics. To fabricate the mHEMT device, a recess process for etching of its Schottky layer was applied before gate metal deposition, and an e-beam lithography using a triple photoresist film for the T-gate structure was employed. We measured DC and RF characteristics of the fabricated device to verify the characteristics that can be used in W-band MMIC design. The mHEMT device exhibited DC characteristics such as a drain current density of 747 mA/mm, maximum transconductance of 1.354 S/mm, and pinch-off voltage of -0.42 V. Concerning the frequency characteristics, the device showed a cutoff frequency of 215 GHz and maximum oscillation frequency of 260 GHz, which provide sufficient performance for W-band MMIC design and fabrication. In addition, active and passive modeling was performed and its accuracy was evaluated by comparing the measured results. The developed mHEMT and device models could be used for the fabrication of W-band MMICs.

A newly proposed T-shape piezoelectric actuator, composed of piezoelectric benders, was designed and studied. This actuator has four legs, and can walk in both forward and backward directions. The piezoelectric actuator has a simple structure and can be easily fabricated. It consists of a piezoelectric bender and a joint. The piezoelectric bender is composed of carbon and ceramic materials. Therefore, there is an advantage in that it can be fabricated on a very small scale. Elliptical displacements of the piezoelectric actuators were analyzed by finite element analysis. Elliptical motion at the tip occurred at two voltages having a 90-degree phase difference. Based on the finite element analysis results, prototype actuators with maximum displacements were fabricated, and the characteristics of their movements were characterized.