Bongchul Kang

Diffuse dielectric anomaly in perovskite-type ferroelectric oxides in the temperature range of 400–700 °C

The diffuse dielectric anomaly by the dielectric relaxation found at the high-temperature region of 400–700 °C was investigated in perovskite-type ferroelectric oxides such as BaTiO3, (Pb,La)TiO3, and (Pb,La)(Zr,Ti)O3 ceramics. We observed that the diffuse dielectric anomaly in perovskite oxides was strongly affected by oxygen-related processing parameters. We have modified the Debye relaxation equation by introducing the mobile dipole of the thermal motion of oxygen vacancies in order to explain the temperature-dependent behavior of the diffuse dielectric anomaly. A relationship between the dielectric polarization/relaxation and the electrical conduction by the thermal motion of oxygen vacancies was microscopically suggested to explain the origin of the diffuse dielectric anomaly found at 400–700 °C in perovskite-type ferroelectric oxides.

Microelectrode fabrication by laser direct curing of tiny nanoparticle self-generated from organometallic ink

In this paper, we present a new laser direct patterning method that selectively cures nanoparticles self-generated from organometallic ink by proper thermal decomposition. This approach has several advantages in the curing rate, resolution and pattern quality compared with the conventional nanoparticle ink based direct laser curing method. It was found that a laser wavelength which is more weakly absorbed by the nanoparticles could produce a more stable and homogeneous curing condition. Finally, arbitrary shaped silver electrodes with narrow width and uniform profile could be achieved on a polymer substrate at a high curing rate of 25 mm/s. This process can be applied for flexible electronics fabrications on heat sensitive polymer substrates.

Adaptive Fabrication of a Flexible Electrode by Optically Self-Selected Interfacial Adhesion and Its Application to Highly Transparent and Conductive Film

A novel adaptive electrode fabrication method using optically self-selected interfacial adhesion between a laser-processed metal layer and polymer film is introduced to fabricate cost-effectively a high-resolution arbitrary electrode with high conductivity. The quality is close to that from vacuum deposition on a highly heat sensitive polymer film, with active response to various design requirements. A highly conductive metal film (resistivity: 3.6 μΩ cm) below a 5 μm line width with a uniform stepwise profile and mirror surface quality (R(rms) : 5-6 nm) is fabricated on a cheap polymer film with a heat resistance limit of below 100 °C. Severe durability tests are successfully completed without using any adhesion promoters. Finally, a highly transparent and conductive electrode with a transparency above 95% and sheet resistance of less than 10 Ω sq⁻¹ is fabricated on a polymer film and on glass by using this method. These results can help realize a potential high-throughput, low-cost, solution-processable replacement for transparent conductive oxides.

Laser-assisted fabrication of single-layer flexible touch sensor

Single-layer flexible touch sensor that is designed for the indium-tin-oxide (ITO)-free, bendable, durable, multi-sensible, and single layer transparent touch sensor was developed via a low-cost and one-step laser-induced fabrication technology. To this end, an entirely novel approach involving material, device structure, and even fabrication method was adopted. Conventional metal oxides based multilayer touch structure was substituted by the single layer structure composed of integrated silver wire networks of sensors and bezel interconnections. This structure is concurrently fabricated on a glass substitutive plastic film via the laser-induced fabrication method using the low-cost organometallic/nanoparticle hybrid complex. In addition, this study addresses practical solutions to heterochromia and interference problem with a color display unit. As a result, a practical touch sensor is successfully demonstrated through resolving the heterochromia and interference problems with color display unit. This study could provide the breakthrough for early realization of wearable device.

High-resolution and high-conductive electrode fabrication on a low thermal resistance flexible substrate

Processes based on the liquid-state pattern transfer, like inkjet printing, have critical limitations including low resolution and low electrical conductivity when fabricating electrodes on low thermal resistance flexible substrates such as polyethylene terephthalate (PET). Those are due to the nonlinear transfer mechanism and the limit of the sintering temperature. Although the laser direct curing (LDC) of metallic inks is an alternative process to improve the resolution, it is also associated with the disadvantages of causing thermal damage to the polymer substrate. This paper suggests the laser induced pattern adhesion transfer method to fabricate electrodes of both high electrical conductivity and high resolution on a PET substrate. First, solid patterns are cost-effectively created by the LDC of the organometallic silver ink on a glass that is optically and thermally stable. The solid patterns sintered on the glass are transferred to the PET substrate by the photo-thermally generated adhesion force of the substrate. Therefore, we achieved electrodes with a minimum line width of 10 ?m and a specific resistance of 3.6 ??cm on the PET substrate. The patterns also showed high mechanical reliability.

Highly effective gold nanoparticle-enhanced biosensor array on the wettability controlled substrate by wiping

We demonstrate the use of a highly effective biosensor array to fulfill the requirements of high intensity, reduced nonspecific adsorption (NSA), and low sample usage. The mixed self-assembled monolayers (SAMs), consisting of methyl-terminated and methoxy-(polyethylene glycol (PEG))-terminated silanes, were newly applied as the background layer to reduce the background NSA via wettability control. The surface was modified by a plasma process with a pattern mask. Gold nanoparticles (AuNPs) were grafted within pattern-modified regions to increase intensity and were modified with protein G variants with cysteine residues to immobilize the antibody proteins directly. The target protein samples were selectively dewetted by the high throughput wiping process, while retaining semi-contact with the substrate. The data revealed that the background NSA was significantly reduced by 78% with selective dewetting compared to the standard method. Furthermore, the peak intensity was improved 5 times by applying AuNPs as ...

High-energy, flexible micro-supercapacitors by one-step laser fabrication of a self-generated nanoporous metal/oxide electrode

A high-performance and flexible micro-supercapacitor based on a self-generated nanoporous silver layer was fabricated by a one-step laser-induced growth-sintering process of a particle-free organometallic solution. The porous structures self-generated on a polymer film and were freely adjustable by controlling the rate of laser input dose. By changing the patterning mode, the nanoporous electrodes with extremely high surface area and highly conductive current collectors were formed in a single processing domain. Electrodeposition of hetero metal oxides (manganese and iron oxides) as the active materials followed, and a flexible micro-supercapacitor with high volumetric energy density of 16.3 mW h cm−3 and power density of 3.54 W cm−3 was formed. This was achieved through the large surface area and high electrical conductivity of the nanoporous silver layer, and high operating voltage due to the asymmetrical electrode configuration. This method resulted in a faster and more cost-effective manufacturing process than conventional MSCs fabrication. It also achieved the highest volumetric energy density in metal/oxide-based MSCs as a state-of-the-art performance.

Heterodyne interference lithography for one-step micro/nano multiscale structuring

A heterodyne interference lithography method using two slightly different wavelengths for one-step multi-scale fabrication of micro/nano hybrid structures is presented. This method has been used to locally fabricate one- and two-dimensional periodical sub-wavelength nanopatterns with a spatial periodicity of several micrometers. Furthermore, multilayered nanostructures with different layer compositions were fabricated by simply controlling the intensity ratio of the two wavelengths. As a result, this method can cost-effectively maximize the degree of freedom of the interference lithography method. The heterodyne interference lithography method can potentially be used in the fabrication of unconventional bio-mimetically engineered surfaces as well as heterocomplexed optics.

Solution-based adaptive parallel patterning by laser-induced local plasmonic surface defunctionalization

Adaptive mass fabrication method based on laser-induced plasmonic local surface defunctionalization was suggested to realize solution-based high resolution self-patterning on transparent substrate in parallel. After non-patterned functional monolayer was locally deactivated by laser-induced metallic plasma species, various micro/nano metal structures could be simultaneously fabricated by the parallel self-selective deposition of metal nanoparticles on a specific region. This method makes the eco-friendly and cost-effective production of high resolution pattern possible. Moreover, it can respond to design change actively due to the broad controllable range and easy change of key patterning specifications such as a resolution (subwavelength~100 μm), thickness (100 nm~6 μm), type (dot and line), and shape.

Parallel laser fabrication of film-embedded microstructures using reusable functionalized template

This study proposes a new parallel mass-production method for obtaining microstructures embedded in flexible films, utilizing a laser-processed reusable functionalized template and a laser-induced adhesive transfer. This physical shape-free template can be cost-effectively fabricated by means of the laser-induced plasmonic defunctionalization of a self-assembled monolayer. The resulting metal nanoparticle microstructure, deposited self-selectively on the template, is transferred to a flexible film by a photo-induced instantaneous interfacial adhesion film in parallel; this process being optimized using molecular dynamics simulations. This method is demonstrated to be capable of the high-efficiency and eco-friendly production of high resolution and durable microstructures in flexible films, using a reusable template to eliminate material waste. Moreover, key design parameters such as the resolution, thickness, type, and shape of microstructures can be actively changed.