Metal sacrificial-layer-assisted transfer is a promising strategy for transferring thermally annealed thin films onto flexible polymer substrates without exposing the receiver substrate to thermal damage. However, stable release of the annealed thin-film stack remains challenging because high-temperature annealing can alter the etching behavior of the sacrificial metal layer and the protective oxide layer. In this study, we propose a thin-film transfer process using a Ni metal sacrificial layer and etch access holes, in which an SU-8/Ti/SiO₂ transferable stack was fabricated on a rigid sapphire donor substrate, annealed at 400–700°C, selectively released by Ni etching, and transferred onto a flexible PET receiver substrate. As the annealing temperature increased from 400 to 700°C, the SiO₂ etch rate decreased from 6.8–6.96 to 2.61–3.83 nm/s, while the Ni release time increased from 72–77 to 82–95 min; nevertheless, the transferable stack was successfully transferred under all process conditions with image-based transfer yields of 58.81–82.76%, with the highest yield obtained for the 200 nm Ni sacrificial layer annealed at 550°C. These results demonstrate the process feasibility of the proposed metal sacrificial-layer and etch-access-hole-based transfer approach for transferring thermally annealed thin-film structures from rigid donor substrates to flexible receiver substrates.

As technologies such as artificial intelligence, autonomous driving, the Internet of Things, wearable electronics, and edge computing continue to spread in the era of the Fourth Industrial Revolution, the importance of hardware security for the safe storage, transmission, and processing of large volumes of data has grown substantially. One of the key components of such security systems is the true random number generator (TRNG), which produces unpredictable random numbers for cryptographic use. In recent years, research on TRNGs has increasingly moved beyond conventional CMOS-based approaches toward semiconductor devices built from emerging materials. These material-based TRNGs offer several advantages, including high integration density, low power consumption, compact form factors, and strong suitability for next-generation edge and IoT environments, because they can directly exploit the intrinsic stochasticity of the device itself as an entropy source. In this review, recent studies on TRNGs based on emerging material-based semiconductor devices are examined from the perspectives of entropy sources, device structures, randomness validation, and wearable/flexible extensions. By bringing together the key physical mechanisms, device platforms, evaluation criteria, and prospects for wearable and flexible electronics in edge and IoT environments, this review aims to provide a useful framework for future research on hardware security devices.

Wearable temperature sensors are becoming increasingly important for continuous health monitoring, personalized healthcare, and biointegrated electronic systems. However, conventional temperature-sensing platforms often suffer from limited thermal sensitivity, insufficient mechanical compliance, and unstable performance under repeated deformation, making it difficult to detect subtle physiological temperature variations in real time. Here, this tutorial status report presents a fabrication strategy for highly sensitive wearable temperature sensors based on gold-doped crystalline silicon nanomembranes. Gold diffusion into crystalline silicon introduces deep-level impurity states that modulate the Fermi level and shift the freeze-out region toward the physiological temperature range, enabling an ultrahigh negative temperature coefficient of resistance. By integrating the gold-doped silicon nanomembrane with a polyimide-supported ultrathin platform, neutral mechanical plane design, and serpentine mesh interconnects, the resulting device can provide high thermal sensitivity, fast response, conformal skin attachment, and stable operation under mechanical deformation. This fabrication approach is expected to broaden the use of impurity-engineered silicon nanomembranes in next-generation wearable sensors, flexible bioelectronics, and multifunctional healthcare monitoring systems.

Flexible and wearable electronics, which require stable operation under mechanical deformation, are increasingly utilizing Eutectic Gallium-Indium (EGaIn) for their conductive components. This study presents a systematic approach to fabricating highly reliable, deformable electrodes via a direct-ink-writing (DIW) 3D printing process using EGaIn as the functional ink. We conducted a thorough optimization of key printing parameters, specifically the extrusion pressure and printing speed, to achieve stable and uniform conductive lines. Through this optimization, we successfully established an optimal process window, achieving a stable line width of approximately 130 μm at an extrusion pressure of 300 kPa and a printing speed of 16 mm/s. The fabricated flexible electrodes exhibited exceptional electromechanical stability, maintaining negligible resistance change (< 0.82%) both under severe bending (3 mm radius) and after 100 repetitive bending cycles. This work demonstrates that the 3D printing of EGaIn is a viable and effective method for creating robust, high-performance electrodes for the next generation of deformable and wearable electronic devices.

Smart electronic skin (E-skin) is an emerging technology that integrates electronic devices with human skin, enhancing human-machine interactions. One critical challenge in its development is effective thermal management to ensure device reliability, longevity, and user comfort. This review highlights passive cooling techniques - thermal conduction, convection, radiation, and phase-change materials - as key strategies to address this challenge without additional power consumption. These integrated mechanisms have demonstrated the ability to efficiently dissipate heat, preventing thermal buildup and maintaining optimal performance in E-skin devices. Recent advancements indicate that combining these methods can significantly enhance the thermal management of flexible electronics. Future research should focus on refining these materials and techniques to overcome challenges related to cost, durability, and environmental stability, thereby advancing the practical application of E-skin technology.

Citations

• Wearable sweat glucose monitoring patches enabled by double network hydrogel-MoS2/PEDOT: PSS nanocomposite
  Suraj Shinde, Omkar A. Patil, Sang Yoon Park, Se Jin Choi, Omkar Pawar, Daniel J. Joe, Sooman Lim, Han Eol Lee
  Microchemical Journal.2025; 215: 114309.     CrossRef

This study proposes an innovative methodology for developing flexible printed circuit boards (FPCBs) capable of conforming to three-dimensional shapes, meeting the increasing demand for electronic circuits in diverse and complex product designs. By integrating a traditional flat plate-based fabrication process with a subsequent three-dimensional thermal deformation technique, we have successfully demonstrated an FPCB that maintains stable electrical characteristics despite significant shape deformations. Using a modified polyimide substrate along with Ag flake-based conductive ink, we identified optimized process variables that enable substrate thermal deformation at lower temperatures (~130℃) and enhance the stretchability of the conductive ink (ε ~30%). The application of this novel FPCB in a prototype 3D-shaped sensor device, incorporating photosensors and temperature sensors, illustrates its potential for creating multifunctional, shape-adaptable electronic devices. The sensor can detect external light sources and measure ambient temperature, demonstrating stable operation even after transitioning from a planar to a three-dimensional configuration. This research lays the foundation for next-generation FPCBs that can be seamlessly integrated into various products, ushering in a new era of electronic device design and functionality.

Next-generation wide-bandgap semiconductors such as SiC, GaN, and Ga₂O₃ are being considered as potential replacements for current silicon-based power devices due to their high mobility, larger size, and production of high-quality wafers at a moderate cost. In this study, we investigate the gradual modulation of chemical composition in multi-stacked metal oxide semiconductor thin films to enhance the performance and bias stability of thin-film transistors (TFTs). It demonstrates that adjusting the Ga ratio in the indium gallium oxide (IGO) semiconductor allows for precise control over the threshold voltage and enhances device stability. Moreover, employing multiple deposition techniques addresses the inherent limitations of solution-processed amorphous oxide semiconductor TFTs by mitigating porosity induced by solvent evaporation. It is anticipated that solution-processed indium gallium oxide (IGO) semiconductors, with a Ga ratio exceeding 50%, can be utilized in the production of oxide semiconductors with wide band gaps. These materials hold promise for power electronic applications necessitating high voltage and current capabilities.

Laser-induced plasmonic sintering of metal nanoparticles (NPs) holds significant promise as a technology for producing flexible conducting electrodes. This method offers immediate, straightforward, and scalable manufacturing approaches, eliminating the need for expensive facilities and intricate processes. Nevertheless, the metal NPs come at a high cost due to the intricate synthesis procedures required to ensure long-term reliability in terms of chemical stability and the prevention of NP aggregation. Herein, we induced the self-generation of metal nanoparticles from Ag organometallic ink, and fabricated highly conductive electrodes on flexible substrates through laser-assisted plasmonic annealing. To demonstrate the practicality of the fabricated flexible electrode, it was configured in a mesh pattern, realizing multi-touchable flexible touch screen panel.

Citations

• Controlling Structures and Properties of NaCl‐Containing Alginate/Polyacrylamide Tough Hydrogels via a One‐Pot Process
  Taeuk Eom, Hyunseung Kim, Jihun Choi, Soon Joo Yoon, Yoon Kyeung Lee, Kwi‐Il Park, Chang Kyu Jeong
  Chemistry – A European Journal.2026;[Epub]     CrossRef
• Wearable sweat glucose monitoring patches enabled by double network hydrogel-MoS2/PEDOT: PSS nanocomposite
  Suraj Shinde, Omkar A. Patil, Sang Yoon Park, Se Jin Choi, Omkar Pawar, Daniel J. Joe, Sooman Lim, Han Eol Lee
  Microchemical Journal.2025; 215: 114309.     CrossRef

Flash lamp annealing (FLA) of metal nanoparticle (NP) ink has provided powerful strategies to fabricate highperformance electrodes on a flexible substrate because of its rapid processing capability (in milliseconds), low-temperature process, and compatibility with to roll-to-roll process. However, metal NPs [e.g., gold (Au), silver (Ag), copper (Cu), etc.] have limitations such as difficulty in synthesizing fine metal NPs (diameter less than 10 nm), high price, and degradation during ink storage and FLA processing. In this regard, organometallic ink has been proposed as a material that can replace metal NPs due to their low-cost (usually 1/100 times cheaper than metal nano inks), low-temperature processability, and high material stability. Despite these advantages, the fabrication of flexible electrodes through FLA treatment of organometallic compounds has not been extensively researched. In this paper, we experimentally guide how to determine the optimal conditions for forming electrodes on flexible substrates by considering material parameters, and flashlight processing parameters (energy density, pulse duration, etc) to minimize the difficulties that may arise during the FLA of organometallic ink.

Perovskite materials are promising candidates for next-generation optoelectronic devices owing to their outstanding external quantum efficiency, high color purity, and ability to tune the light emission wavelength. However, conventional thermal annealing processes caused the degradation of perovskite, resulting in poor optoelectronic properties and a short lifetime. Herein, we propose a laser-induced recrystallization of perovskite thin film to enhance its light-emitting properties. Laser-induced recrystallization process was performed using rapid and instantaneous laser heating, which successfully induced grain growth of the perovskite material. The laser processing conditions were thoroughly optimized based on theoretical calculations and various material analyses such as x-ray diffraction, scanning electron microscope, and photoluminescence spectroscopy.

With the advent of the IoT (internet of things) era, there has been discussion on how to efficiently use various information from daily life. In academic and industrial society, various smart devices such as smart watches, smart phones, and smart glasses have been developed and commercialized for narrowing the physical/psychological distance with user information. According to recent developments of smart devices, the contemporary people have desired to check their body information and treat disease by themselves. According to the needs of the time, biological researches by phototherapy/monitoring have been actively conducted. Among various light sources, microLEDs have been spotlighted due to their superior optoelectric properties and stability. In this paper, we would like to review the state-of-the research results on the next-generation biological therapy devices via microLEDs.

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.

In this study, we developed the solution-processed PMMA-HfOx hybrid ReRAM devices to overcome the respective drawbacks of organic and inorganic materials. The performances of PMMA-HfOx hybrid ReRAM were compared to those of PMMA- and HfOx-based ReRAMs. Bipolar resistive switching behavior was observed from these ReRAMs. The PMMA-HfOx hybrid ReRAMs showed a larger operation voltage margin and memory window than PMMA-based and HfOx-based ReRAMs. The reliability and electrical instability of ReRAMs were remarkably improved by blending the HfOx into PMMA. An Ohmic conduction path was commonly generated in the LRS (low resistance state). In HRS (high resistance state), the PMMA-based ReRAM showed SCLC (space charge limited conduction). the PMMA-HfOx hybrid ReRAM and HfOx-based ReRAM revealed the Pool-Frenkel conduction. As aresult of flexibility test, serious defects were generated in HfOx film deposited on PI (polyimide) substrate. On the other hand, the PMMA and PMMA-HfOx films showed an excellent flexibility without defect generation.