Jeung Sang Go

A novel fabrication of in-channel 3-D micromesh structure using maskless multi-angle exposure and its microfilter application

This paper presents a novel fabrication method of in-channel three-dimensional micromesh structures using the conventional photolithography. The micromesh was realized by exposing UV light from the backside of the SU-8 coated metal-patterned glass substrate for different angles. Numbers of exposure and irradiation angle decided the shape and the size of micromesh. Based on this technique, three different micromesh-inserted microchannel structures were fabricated. For hydrodynamic characterization, their flow resistances were measured. Finally, for the application of micro total analysis system (/spl mu/TAS), the microfilter was fabricated and its filtering property was demonstrated.

Design of a microfin array heat sink using flow-induced vibration to enhance the heat transfer in the laminar flow regime

This paper presents design guidelines for a microfin array heat sink using flow-induced vibration to increase the heat transfer rate in the laminar flow regime. Effect of the flow-induced vibration of a microfin array on heat transfer enhancement was investigated experimentally by comparing the thermal resistances of the microfin array heat sink and those of a plain-wall heat sink. At the air velocities of 4.4 and 5.5 m/s, an increase of 5.5 and 11.5%, respectively, in the heat transfer rate was obtained. The microfin flow sensor also characterized the flow-induced vibration of the microfin. It was determined that the microfin vibrates with the fundamental natural frequency regardless of the air velocity. It was also shown that the vibrating displacement of the microfin is increased with increasing air velocity and then saturated over a certain value of air velocity. Based on the numerical analysis of the temperature distribution resulting from microfin vibration and experimental results, a simple heat transfer model (heat pumping model) was proposed to understand the heat transfer mechanism of a microfin array heat sink. Under the geometric and structural constraints, the maximum heat transfer enhancement was obtained at the intersection of the minimum thickness of the microfin and constraint of the bending angle.

Dry etching of polydimethylsiloxane using microwave plasma

This paper presents a new polydimethylsiloxane (PDMS) dry-etching method that uses microwave plasma. The applicability of the method for fabricating microstructures and removing residual PDMS is also verified. The etch rate of PDMS was dominantly influenced by the gas flux ratio of CF4/O2 and the microwave power. While the PDMS etch rate increased as the flux ratio of CF4 was increased, the etch rate decreased as the flux ratio of O2 was increased. The maximum etch rate of 4.31 µm min−1 was achieved when mixing oxygen (O2) and tetrafluoromethane (CF4) at a 1:2 ratio at 800 W power. The PDMS etch rate almost linearly increased with the microwave power. The ratio of the vertical etch rate to the lateral etch rate was in a range of 1.14–1.64 and varied with the gas fluxes. In consideration of potential applications of the proposed PDMS etching method, array-type PDMS microwells and network-type microprotrusion structures were fabricated. The contact angle was dramatically increased from 104° (non-etched PDMS surface) to 148° (etched PDMS surface) and the surface was thereby modified to be superhydrophobic. In addition, a thin PDMS skin that blocked holes and PDMS residues affixed in nickel microstructures was successively removed.

A disposable, dead volume-free and leak-free monolithic PDMS microvalve

A new fabrication method of a membrane-inserted pneumatically-driven microvalve is presented. The device is entirely made from PDMS. To ensure dead volume-free and leak-free, the valve chamber is formed with smooth surface using molding of UV-curable bond. Also, to place a PDMS membrane on the molded PDMS substrate, bonding with spin-coated PDMS membrane is performed, indicating to align-less assembly. As a reference of bonding characterization, the curing ratio, defined as the ratio of soft bake time and hard cure time of PDMS at the same soft cure temperature, is introduced. The best bonding feature is obtained at the curing ratio of 0.06. The maximum tensile bonding strength is examined. Finally, the performance of the membrane-inserted monolithic PDMS valve is tested.

Surface Wettability in Terms of the Height and Depression of Diverse Microstructures and Their Sizes

Surface wettability in terms of the height, depression, and sizes of diverse microstructures was examined. We considered three different types of microstructures: square pillars, square pores, and hexagonal pores. An increase in pore fraction causes a decrease in the contact area between a water drop and the microstructures, resulting in an increase in contact angle. It was verified that the contact angle of the square pillar microstructure is higher than those of the square pore and hexagonal pore microstructures for the same pore fraction. Of the pore-based microstructures, the square-pore microstructure has a higher contact angle than the hexagonal pore microstructure. However, it was observed that water drops were more stable with respect to pore fraction on the hexagonal pore microstructures. In addition, compared with the pillar microstructure, the pore-based microstructures exhibited more stable contact angles for different structure heights.

Hollow-core polymeric nanoparticles for the enhancement of OLED outcoupling efficiency

Abstract This work presents the possibility of the hollow core nanoparticles to improve luminance in an organic light emitting diode device. The finite difference time domain simulation estimates the effect of the hollow core nanoparticles on the external quantum efficiency of the organic light emitting diode device. The efficiency depends on the size and the volume fraction of the hollow core nanoparticles in the polymer layer, together with the refractive index and the thickness of the polymer layer. It is shown that the hollow core nanoparticles dispersed in a polymer layer can enhance the external quantum efficiency by a factor of 2.5. This work also introduces a continuous production method of the hollow core nanoparticles by using the microfluidic self-assembly of amphiphilic polymers and the layer formation dispersed with them for the rigorous light scattering.

Formation of polymeric hollow microcapsules and microlenses using gas-in-organic-in-water droplets

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

Direct Micro Fabrication of Flexible Copper Clad Laminate Using 355 nm UV Laser

In the study for this paper, the 355 nm UV laser was used to modify and to deposit copper patterns onto a polyimide surface. The UV laser breaks chemical bonds and causes chemical reactions to occur on the irradiated surface due to photochemical effects and to photothermal effects. More specifically, the polyimide surface is initially modified using the UV laser and the copper is then deposited directly by the UV laser from the copper formate solution. The polyimide surface was transformed into an oxygen-rich surface by modification and copper traces were deposited on the polyimide surface. The smallest pattern was obtained at a laser fluence of 600 mJ/cm2 and a scan speed of 4.3 mm/s. The maximum thickness was 8.5 µm and the width was 55 µm. While the thickness and the width of the deposited copper traces decreased in accordance with the scan speed of the laser, the surface of the deposited copper traces is extremely rough. Furthermore, the copper had C and O impurities. The resistivity of copper traces was minimum 1.07 ×10-6 Ωm.

Synthesis fluorescent magnetic nanoparticles in a microchannel using the La Mer process and the characterization of their properties

This study presents a stable and controllable synthesis of fluorescent magnetic nanoparticles in a flow-through microchannel for the bimodal use of magnetic activated cells sorting and fluorescence-activated cell sorters. The La Mer process is carried out to synthesize magnetic nanoparticles using co-precipitation. Then, the magnetic nanoparticles are coated with conjugation of chitosan and fluorescent isothiocyanate with two different concentrations. The chemical composition of the magnetic nanoparticles is determined by comparing the standard X-ray diffraction peaks of Fe3O4, and their sizes are also examined by using field emission scanning electron microscopy and dynamic light scattering measurement. The magnetic property of saturation magnetization and coercive field is characterized in a vibrating sample magnetometer. Also, the possibility of external manipulation in the synthesis of the magnetic particles is demonstrated by separating the synthesized fluorescent magnetic nanoparticles into a non-reacting lamination flow. Finally, their fluorescence property is determined by measuring the fluorescence adsorption spectra and the photoluminescence emission spectra in UV–Vis spectroscopy.

Direct fabrication of thin film gold resistance temperature detection sensors on a curved surface using a flexible dry film photoresist and their calibration up to 450 °C

High efficiency heat exchangers, such as intercoolers and recuperators, are composed of complex and compact structures to enhance heat transfer. This limits the installation of conventional temperature sensors to measure the temperature inside the heat exchanger without flow disturbance. To overcome this limitation, we have developed a direct patterning method in which metal is sputtered onto a curved surface using film photoresist and the fabrication of thin film Au resistance temperature detection (RTD) temperature sensors. A photosensitive film resist has been used to overcome the difficulty of 3-dimensional photolithography on a curved surface. The film resist after 2-dimensional photolithography is laminated over an alumina rod which is deposited with Au as an RTD sensing material. The Au metal is etched chemically, and the film resist is removed to form the thin film Au-RTD temperature sensors. They are calibrated by measuring the resistance change against temperature in a thermally controlled furnace. The second order polynomial fit shows good agreement with the measured temperatures with a standard deviation of 0.02 for the temperature range of 20–450 °C. Finally, the performance of the Au-RTD temperature sensors was evaluated.