Hae-Sung Kim

Two-dimensional photonic crystal color filter development

Reflective color filters using two-dimensional photonic crystals based on sub-wavelength gratings were proposed and constructed. Using low-cost nanoimprint lithography, an amorphous silicon layer was deposited through the low-temperature PECVD process and patterned into two-dimensional structures. The isolated amorphous silicon patterns were readily crystallized using a multi-shot excimer laser annealing at low energy. A study of the close relationship between color filter reflectance and silicon pattern crystallinity is introduced. Theoretical and experimental results show that the proposed color filters have high reflectance and, moreover, decrease the dependence on incident angle compared to one-dimensional photonic crystal color filters.

High angular tolerant color filter using subwavelength grating

A reflective color filter based on a two-dimensional subwavelength grating is proposed. The filter has been designed by performing numerical simulations and has been fabricated on 5×5 mm2 quartz glass using electron beam lithography. The grating color filter shows reflectance of 74% and spectral width of about 80 nm. Furthermore, it has good angular tolerance, up to ±45°, for unpolarized incident light. By analyzing the reflectance spectral distributions in the band diagram, we found that high angular tolerance is achieved due to the high refractive index contrast of grating structures.

The fabrication of Co-Pt electro-deposited bit patterned media with nanoimprint lithography.

Bit patterned media with 25 nm hole diameter and 50 nm pitch size were fabricated with serial processes comprising master patterning with electron-beam lithography, a Si etching process, multi-layer soft stamp replication, and UV nanoimprinting, followed by Co-Pt magnetic material filling by electro-deposition. From these processes, the designed patterns were well defined, and perpendicular magnetic anisotropy of the fabricated bit patterned media was obtained.

Development of Microlens for High-Density Small-Form-Factor Optical Pickup

A microlens of numerical aperture (NA) 0.85 a small-form-factor optical pickup, following the specifications of the Blu-ray disc (BD), was designed, fabricated and evaluated. To avoid difficulties in the fabrication of a high-NA objective lens and to obtain a low chromatic aberration, a new hybrid lens unit was designed to have a refractive lens and a diffractive lens. The micro-plano-aspheric refractive lens was fabricated using glass molding technology, and the diffractive lens was fabricated in a two-dimensional array using the electron beam mastering and consecutive UV embossing process. For the evaluation of the developed lens unit, diffraction efficiency was measured with the proposed diffraction efficiency measurement method, and the wavefront error of the lens unit was evaluated using a modified Mach–Zehnder interferometer. The measured average efficiency of the diffractive lens was approximately 85% and the RMS wavefront error of the lens unit was 0.0376 λrms.

Single crystal-like Si patterns for photonic crystal color filters

A novel fabrication method for a two-dimensional photonic crystal color filter based on guided mode resonance is proposed. An amorphous silicon layer deposited through the low-temperature plasma enhanced chemical vapor deposition (PECVD) process is patterned into two-dimensional structures using low-cost nanoimprint lithography. It is then effectively crystallized using multi-shot excimer laser annealing at low energy. We have demonstrated analytically and experimentally that single crystal-like silicon patterns on a glass substrate can offer high-efficiency photonic crystal color filters for reflective display applications. The highly crystallized silicon patterning scheme presented here may be very attractive for a variety of devices requiring high carrier mobility and high optical efficiency.

Super slim optical pickup for mobile storage device applications

This paper addresses the design, fabrication and packaging issues of SSOP(super slim optical pickup) module using blury technology. By using blu-ray technology, which uses a 407nm LD (Laser Diode) and an objective lens having NA (Numerical Aperture) 0.85, storage devices become miniaturized but have a high capacity. The developed prototype uses the integrated structure of a SiOB (Silicon Optical Bench) and a mirror substrate. The SiOB should be processed in order that a thin film PD(Photodiode) and interconnections, LD, Lens, QWP(Quarter Wave Plate) and HOE can be placed, and on the Silicon Substrate should Micromachined Silicon Mirror be formed. The SiOB is aligned and bonded with the wafer on which Silicon Mirror was formed. Then, it is diced. Because it is fabricated through this order, the super slim optical pickup can be fabricated by using wafer-level process. As a final step LD on the SiOB and HOE are mounted, assembled and bonded using an active alignment. The proposed SSOP was prototyped and characterized by measuring wavefront error and detecting static focusing and tracking error signals.

Diffraction limit of the focusing waveguide grating coupler for optical probe information storage

A focusing waveguide grating coupler (FWGC) has been applied to an optical information storage element. To achieve minimum diffraction, focusing and high-coupling efficiency with high power, several fabrication and design difficulties have to be overcome. In this work, we report some new strategies to improve the fabrication and design, and greatly improve the pattern quality in defining curved gratings in the nanometre range using single-step electron-beam lithography with a conventional exposure mode. We also present the optimum fabrication conditions for the FWGC and the minimum diffraction limit (1.1 µm) obtained for the structure, which is optically the smallest diffraction spot size obtainable from diffraction gratings focusing beams into a spot in air.

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.