Hak-Rin Kim | Kyungpook National University (original) (raw)

Papers by Hak-Rin Kim

SID Symposium Digest of Technical Papers, 2011

In this paper, we demonstrate a new surface patterning method for controlling the azimuthal ancho... more In this paper, we demonstrate a new surface patterning method for controlling the azimuthal anchoring energy and pretilt of liquid crystal alignment layer using topologically mixed surface patterns. In our method, the micro‐groove structure is spontaneously formed by the preparation, where the macro‐groove and micro‐groove surface pattern determine the surface pretilt and the azimuthal LC anchoring, respectively.

Crystals

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimid... more In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) LC modes with negative dielectric LC (n-LC), delicate material engineering is required to avoid surface-charge-dependent image flickering and sticking problems, which severely degrade with lowering operation frequency. Therefore, this paper proposes a photocontrolled variable-resistivity PI layer in order to systematically investigate the voltage holding and discharging properties of the FFS n-LC modes, according to the PI resistivity (ρ) levels. By doping fullerene into the high-ρ PI as the photoexcited charge-generating nanoparticles, the ρ levels of the PI were continuously controllable with a wide tunable range (0.95 × 1015 Ω∙cm to 5.36 × 1013 Ω∙cm) through Ar laser irra...

2020 IEEE International Conference on Consumer Electronics (ICCE), 2020

A bi-focal geometric phase (GP) lens can be used to improve the depth range of an integral floati... more A bi-focal geometric phase (GP) lens can be used to improve the depth range of an integral floating display to form switchable depth planes. However, due to a chromatic aberration of a GP lens to form R/G/B sub-images at different locations, a color breaking of floated image can occur. In this paper, we propose a novel method to compensate that chromatic aberration by integrating R/G/B pixels at depths.

Polymer Journal, 2020

To develop highly sensitive updatable hologram materials, an azobenzene monomer was synthesized h... more To develop highly sensitive updatable hologram materials, an azobenzene monomer was synthesized herein that supports effective photoisomerization under visible green beam irradiation. Furthermore, an acetylene group was introduced via Sonogashira coupling for higher birefringence. Polymerization was performed on the synthesized azobenzene monomer and on the methyl methacrylate (MMA) monomer, which serves as the skeleton of the film. The structures of all molecules were characterized by nuclear magnetic resonance (NMR) spectroscopy, and UV-Visible absorption spectroscopy was performed to analyze their optical properties. The holographic writing and rewriting capabilities of the newly synthesized azobenzene side-chain polymer were characterized by using a green laser as a writing beam, which showed that a high diffraction efficiency was reliably achievable under low-energy laser irradiation when evaluated with a four-wave-mixing optical scheme. In this study, high birefringent acetylene group containing azobenzene-based polymers were synthesized as materials for rewritable green-laser holograms, and their properties were evaluated. Birefringence change of polymer, which has an absorption wavelength suitable for green laser (532 nm), is 0.018. The diffraction efficiency of polymer was 72% under low-energy irradiation (7 J/cm2). These results show that the hologram recording material made in this study with high birefringent azobenzene are stable, without undergoing decomposition even when repeated recording and rewriting were performed.

Physical chemistry chemical physics : PCCP, Jan 25, 2018

We derived a new analytic physical model for describing the temperature-dependent dielectric perm... more We derived a new analytic physical model for describing the temperature-dependent dielectric permittivities εe(T) and εo(T) in anisotropic mesophase molecules of nematic liquid crystals (NLCs). These temperature-dependent dielectric properties of NLCs could be explained by a six-parameter dielectric permittivity model, where the analytic dielectric permittivity curves of εe(T), εo(T), and Δε(T) from the model using the six parameters ε*, Aε, Bε, (Δε)o, λε, and T* showed excellent agreement with experimental data. The six-parameter dielectric permittivity model was compared to the conventional four-parameter refractive index model. To systematically investigate the temperature-dependent properties of the refractive indices (ne(T) and no(T)) and dielectric permittivities according to the molecular structure of the NLCs, four similar types of fluorinated phenyl bicyclohexane NLCs were selected. Using the presented models, the temperature-dependent behaviour of these four fluorinated NL...

Renewable Energy and Power Quality Journal, 2011

In this paper, we fabricated organic solar cells using spray-coating with substrate heated method... more In this paper, we fabricated organic solar cells using spray-coating with substrate heated method. We heated substrate temperature to 50 °C, 100 °C, and 150 °C respectively, during spray-coating process and observed different morphologies of the active layer. The difference of morphologies affected the performance of the organic solar cell. One of these samples, substrate heated as 150 °C, showed an open voltage of 0.61 V, short current density of 20 mA/cm 2 and power conversion efficiency of 3.84%.

Journal of Sensor Science and Technology, 2007

Journal of the Optical Society of Korea, 2016

We present a polarization-dependent prism array film for controlling the viewing angle distributi... more We present a polarization-dependent prism array film for controlling the viewing angle distribution of liquid crystal (LC) display panels without loss of light efficiency. On a directional backlight unit, our polarization-dependent prism array film, made into a stacked bilayer with a well-aligned liquid crystalline reactive mesogen (RM) layer on the UV-imprinted prism structure, can continuously control the light refraction function of the prism array by electrically switching incident polarization states of a polarization-controlling layer prepared by a twisted nematic LC mode. The viewing angle control properties of the polarization-dependent prism array film are analyzed under different prism angle and refractive index conditions of the RM layer. A simple analytic model is also presented to describe the intermediate viewing angle distributions with continuously varying applied voltages and incident polarization states.

Phase Transitions, 2016

ABSTRACT We studied the structural order in randomly perturbed nematic liquid crystals using a ra... more ABSTRACT We studied the structural order in randomly perturbed nematic liquid crystals using a random anisotropic nematic-type lattice model. Simulations were carried out at zero temperature and at various other temperatures, for which we varied the concentration of impurities p, anchoring strength W and imposed external strength fields B at two different histories: temperature-quenched history (TQH) and field-quenched history. The Haller approximation method utilized the temperature dependence of the order parameter to determine the pseudo-critical exponent β at different values of p and W. Consequently, the values of β increased when p and W were increased. Additionally, applying an external field B for investigating the parameters revealed that the TQH established long-range order for high magnitudes of B at zero temperature (T* = 0) and T* = 0.5.

We have demonstrated the novel technique for spacing two flexible substrates in stable by using r... more We have demonstrated the novel technique for spacing two flexible substrates in stable by using rigid pillar spacer array and micro-contact printing assembling technique. Specially designed columnar structure generates self-collected adhesive polymer feature results in a good adhesion and a high mechanical stability to the external bending deformations.

Journal of Information Display, 2010

This paper presents the effects of a dielectric layer and an electrolyte on the driving performan... more This paper presents the effects of a dielectric layer and an electrolyte on the driving performance of an electrowetting on dielectric (EWOD)‐based liquid lens. The range of tunable focal length of the EWOD‐based liquid lens was highly dependent on the conditions of the dielectric layer, which included an inorganic oxide layer and an organic hydrophobic layer. Moreover, experiments on the

2014 International Symposium on Optomechatronic Technologies, 2014

We demonstrate a fabrication method of multi-focusing micro lens array (MLA) through thermal refl... more We demonstrate a fabrication method of multi-focusing micro lens array (MLA) through thermal reflow method, and its optical properties. In our multi-focusing MLA, each lens structure was hexagonally packed, and we introduced a partial developing process and a confinement wall structure made by cross-linked photo resist (PR) material to fix a diameter of reflowed spherical lens structure. Due to the base PR layer supporting the thermal reflow process and the guiding structure, the thermally reflowed PR lens structure has different radius of curvatures with different numerical apertures (NAs), where the reflowed PR lens structure could be precisely modeled by the initial volume of the double cylinder PR structure. The multi-focusing MLA we fabricated by using ultraviolet (UV) curable polymer with 1.51 refractive index had four different focal lengths of which values were 0.9 mm, 1.1 mm, 1.6 mm and 2.5 mm, respectively, with four different NAs of which values were 0.1799, 0.2783, 0.3973 and 0.4775, respectively, where the fill factor was 0.7727.

8th International Conference on Electrical and Computer Engineering, 2014

We presented improved density and aspect ratio of ZnO nanowires which were hydrothermally grown o... more We presented improved density and aspect ratio of ZnO nanowires which were hydrothermally grown on spin coated ZnO seed layer. After UVO treatment on silicon surface, spin coated ZnO seed layer showed a high coverage density due to increased surface wettability without forming island like growth in conventional method. ZnO active nucleation sites showed a positive increasing relation with increase in coverage density. Whereas, increased spin coating time had risen surface roughness with rise in coverage area, UVO treated surface wettability change had showed lower surface roughness. Moreover, seed layer thickness remained unaffected for surface wettability changing effect. This let ZnO nanowires grow on the increased ZnO active nucleation sites without hindrance of other nanowires. Hence, higher density and aspect ratio ZnO nanowires were achieved by controlling surface wettability via UVO treatment.

SPIE Newsroom, 2012

Using oblique beams with two prism sheets produces a special bluephase liquid crystal mode that s... more Using oblique beams with two prism sheets produces a special bluephase liquid crystal mode that solves problems of high operating voltage, low brightness, and hysteresis switching.

2007 Asia Optical Fiber Communication and Optoelectronics Conference, 2007

ABSTRACT We developed a simple and versatile patterning method for advanced organic displays with... more ABSTRACT We developed a simple and versatile patterning method for advanced organic displays with high resolution and uniformity in large area. Our patterning method involves the optical formation of selective wetting regions, where a regular array of functional polymer patterns is obtained by a standard spin-casting process. It is demonstrated that polymeric semiconductors and light-emitting polymers can be patterned to produce periodic arrays with feature resolution down to sub-micrometers using the selective wettability. This wettability-based patterning technique of soluble functional polymers would be directly applicable for organic displays and plastic electronics.

MRS Proceedings, 2006

To detect biological events, biosensors require a transducer part where specific biomolecular bin... more To detect biological events, biosensors require a transducer part where specific biomolecular binding events at a bioreceptor part is converted to measurable quantitative signals. Currently, most of biosensors adopt a fluorescent or radioactive probing technique as a transducer. However, such approaches require expensive and sophisticated analysis procedures with laboratory-based equipment.In this work, we propose a novel method for optically detecting hybridization results in a deoxyribonucleic acid (DNA) chip using an anchoring transition of liquid crystal (LC) alignment. To investigate the effects of structural changes of DNA on the LC alignment, we used a functional substrate on which single-stranded oligonucleotide DNA (ssDNA) was selectively immobilized to a Biotin Chip substrate. In our experiment, we used a 19-mer oligoDNA or p53 tumor suppressor as a bioreceptor and its complementary partner oligoDNA as a target material.Before hybridization, surface nematic LC (NLC) molecu...

ABSTRACT An electrolyte-based dual-axis tilt sensor has been newly designed, fabricated using mic... more ABSTRACT An electrolyte-based dual-axis tilt sensor has been newly designed, fabricated using micro electro mechanical systems (MEMS) technique and reported in this paper. For tilt detection on two axes, four sensing electrodes have been formed on the four sidewalls of the truncated pyramid cavity and a common electrode at the bottom of the cavity for contacting the electrolyte through a via-hall. The measured characteristic of the tilt sensor demonstrates approximately 50 mV of change in the output voltage per degree of inclination angle in ±70° of operating angle range on two axes.

Optical Engineering, 2003

... [bold Yonghyun Kim] received his BS degree with summa cum laude in ... In 1994 he joined the ... more ... [bold Yonghyun Kim] received his BS degree with summa cum laude in ... In 1994 he joined the faculty of the School of Electrical Engineering, Seoul National University, where he is now an associate professor. ... In 2002 he received the Presidential Young Scientist Award of Korea. ...

Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, 1999

ABSTRACT

Japanese Journal of Applied Physics, 2010

In this paper, we propose methods to enhance the durability of a microelectromechanical system (M... more In this paper, we propose methods to enhance the durability of a microelectromechanical system (MEMS)-based liquid droplet lens driven by electrowetting. The enhanced durability of the lens is achieved through not only improvement in quality of dielectric layer for electrowetting by minimizing concentration of coarse pinholes, but also mitigation of physical and electrostatic stresses by reforming lens cavity. Silicon dioxide layer is deposited using plasma enhanced chemical vapor deposition, splitting the process into several steps to minimize the pinhole concentration in the oxide layer. And the stresses-reduced cavity in a form of overturned tetra-angular truncated pyramid with rounded corners, which is based on simulated results, is proposed and realized using silicon wet etching processes combined into anisotropic and isotropic etching.