Eikhyun Cho

Design methodology accounting for fabrication errors in manufactured modified Fresnel lenses for controlled LED illumination

The increasing demand for lightweight, miniaturized electronic devices has prompted the development of small, high-performance optical components for light-emitting diode (LED) illumination. As such, the Fresnel lens is widely used in applications due to its compact configuration. However, the vertical groove angle between the optical axis and the groove inner facets in a conventional Fresnel lens creates an inherent Fresnel loss, which degrades optical performance. Modified Fresnel lenses (MFLs) have been proposed in which the groove angles along the optical paths are carefully controlled; however, in practice, the optical performance of MFLs is inferior to the theoretical performance due to fabrication errors, as conventional design methods do not account for fabrication errors as part of the design process. In this study, the Fresnel loss and the loss area due to microscopic fabrication errors in the MFL were theoretically derived to determine optical performance. Based on this analysis, a design method for the MFL accounting for the fabrication errors was proposed. MFLs were fabricated using an ultraviolet imprinting process and an injection molding process, two representative processes with differing fabrication errors. The MFL fabrication error associated with each process was examined analytically and experimentally to investigate our methodology.

Effects of Fabrication Errors on the Sensitivity of Nano-Replicated Guided Mode Resonance Protein Sensors

Although an injection molding is a promising method for inexpensive mass production of nanograting substrate for disposable guided mode resonance (GMR) protein sensor, the incomplete filling of nanocavities due to the thick solidified layer in conventional injection molding process may lower the sensitivity of label-free GMR protein sensor. In this study, an instant heating method at the filling stage during the injection molding process was investigated to improve the pattern transcribability of molded nanograting and the sensitivity of fabricated GMR protein sensor. Two types of injection molded nanograting with and without instant heating method were prepared and the effects of pattern fidelity on the performance of fabricated GMR protein sensor were analyzed by theoretical and experimental methods.

Label-free detection of protein-protein interactions on multi-scale micro-well arrays using spatial light modulator

A mass production method of label-free protein microarray integrated with micro-well structures for the use of miniaturized multi-parallel scanning system was investigated. The geometrical parameters of biosensing structure were designed by rigorous coupled wave analysis simulation, and micro-well structures were designed considering the detection and material delivery system. The protein microarray with micro-well structures was fabricated by one-step UV nanoimprinting process using an electroformed multi-scale metallic stamp. Finally, microarray scanning was achieved using optical modulation without applying any motorized system and the feasibility of proposed protein microarray and scanning system was demonstrated by verifying the bio-molecular interactions.

Design and fabrication of a metallic nanostamp using UV nanoimprinting and electroforming for replicating discrete track media with feature size of 35 nm

The demand for high-density data-storage media is increasing, necessitating the development of novel magnetic data-storage technologies. Among the various types of storage media, discrete track media (DTM) is an emerging technology that is being used to overcome the limitations of conventional continuous magnetic data-storage technology, such as the superparamagnetic effect and medium noise. In this study, the authors propose a method of fabricating a metallic stamp for replicating DTM patterns using ultraviolet (UV) nanoimprinting and electroforming, which are inexpensive processes that can be used to fabricate nanostructures with high precision. First, a silicon nanomaster with a feature size of 35 nm and a pitch of 70 nm was designed and fabricated by electron-beam recording and inductively coupled plasma etching. The measured pitch of the silicon master was 71.6 nm. Then, a polymeric master with a full track of nanoline patterns was then replicated from the silicon nanomaster via UV nanoimprinting. To...

Effect of alumina composition and surface integrity in alumina/epoxy composites on the ultrasonic attenuation properties

We report a method of fabricating backing blocks for ultrasonic imaging transducers, using alumina/epoxy composites. Backing blocks contain scatterers such as alumina particles interspersed in the epoxy matrix for the effective scattering and attenuation of ultrasound. Here, the surface integrity can be an issue, where the composite material may be damaged during machining because of differences in strength, hardness and brittleness of the hard alumina particles and the soft epoxy matrix. Poor surface integrity results in the formation of air cavities between the backing block and the piezoelectric element upon assembly, hence the increased reflection off the backing block and the eventual degradation in image quality. Furthermore, with an issue of poor surface integrity due to machining, it is difficult to increase alumina as scatterers more than a specific mass fraction ratio. In this study, we increased the portion of alumina within epoxy matrix by obtaining an enhanced surface integrity using a net shape fabrication method, and verified that this method could allow us to achieve higher ultrasonic attenuation. Backing blocks were net-shaped with various mass fractions of alumina to characterize the formability and the mechanical properties, including hardness, surface roughness and the internal micro-structure, which were compared with those of machined backing blocks. The ultrasonic attenuation property of the backing blocks was also measured.

Formation of multilayered magnetic nanotracks with perpendicular anisotropy via deoxidization using ion irradiation on ultraviolet-imprinted intaglio nanostructures

We proposed a method to fabricate perpendicular magnetic nanotracks in the cobalt oxide/palladium multilayer films using UV-nanoimprinting lithography and low-energy hydrogen-ion irradiation. This is a method to magnetize UV-imprinted intaglio nanotracks via low-energy hydrogen ion irradiation, resulting the irradiated region are magnetically separated from the non-irradiated region. Multilayered magnetic nanotracks with a line width of 140 nm, which were fabricated by this parallel process without additional dry etching process, exhibited a saturation magnetization of 290 emu cm−3 and a coercivity of 2 kOe. This study demonstrates a cost-effective mass production of multilayered perpendicular magnetic nanotracks and offers the possibility to achieve high density storage and memory devices.

Fabrication and evaluation of label-free protein sensor for diagnosing acute myocardial infarction

We proposed a method to fabricate label-free protein sensor with sub-wavelength nanograting structures to be used for diagnosing acute myocardial infarction. A nickel stamp for the injection molding of nanograting integrated protein sensor was fabricated by electroforming process with high fidelity. By using metallic stamp, we replicated label-free protein sensor via injection molding, which is an outstanding method for low-cost and mass production of polymer products. Finally, we performed a feasibility test, examining cardiac troponin T (cTnT) and anti-cTnT interactions. From the results, we demonstrated that the fabricated protein sensor can provide information for the early and accurate detection of cardiac diseases such as acute myocardial infarction.

The effect of nano grating shapes on the sensitivity of guided mode resonance protein sensor fabricated by nano injection molding process

We investigated the effect of nano grating shapes on the sensitivity of nano injection molded guided-mode-resonance protein sensor. To confirm the profile effects, we performed design, fabrication and performance evaluation.

Replication of label-free guided mode resonance filter for protein-sensors using UV nanoimprinting process with metallic nano stamp

Interest in protein sensors using guided-mode resonance (GMR) filters is rapidly growing as the demand for sensitive and reliable protein sensors increases in clinical diagnostic applications and pharmaceutical research. GMR filter-based protein sensors are capable of high sensitivity in the detection of molecular interactions, by measuring the movement of sharp reflectance peaks. We designed a GMR filter by computer simulation, and created a prototype by UV nanoimprinting, using a highly durable metallic nano stamp, which was fabricated by electroforming process with a polymeric master pattern. We also demonstrated the use of this GMR filter as a protein sensor by measuring the peak wavelength value (PWV) and the PWV shift.