Joo-Do Park

Fabrication of a 50 nm half-pitch wire grid polarizer using nanoimprint lithography

We report the fabrication of a 50 nm half-pitch wire grid polarizer with high performance using nanoimprint lithography. The device is a form of aluminium gratings on a glass substrate whose size of 5.5 cm × 5.5 cm is compatible with a microdisplay panel. A stamp with a pitch of 100 nm was fabricated on a silicon substrate using laser interference lithography and sidewall patterning. The imprint and the aluminium etching processes are optimized to realize uniform aluminium gratings with aspect ratio of 4. The polarization extinction ratio of the fabricated device is over 2000, with transmission of 85% at a wavelength of 450 nm, which is the highest value ever reported. This work demonstrates that nanoimprint lithography is a unique cost-effective solution for nanopatterning requirements in consumer electronics components.

Color filter incorporating a subwavelength patterned grating in poly silicon

A color filter based on a subwavelength patterned grating in poly silicon was proposed and realized on a quartz substrate. It was produced by utilizing the laser interference lithography technique to feature wide effective area compared to the costly e-beam lithography. An oxide layer was introduced on top of the silicon grating layer as a mask to facilitate the silicon-etching and to enhance the filtering selectivity as well. The structural parameters for the device include the grating pitch and height of 450 nm and 100 nm respectively, the silicon stripe width of 150 nm, and the oxide thickness of 200 nm. The fabricated device offered a spectral response suitable for a blue color filter, exhibiting the center wavelength of approximately 460 nm, the bandwidth approximately 90 nm and the peak transmission 40%. The positional dependence of its performance was examined to find the effective area of 3 x 3 mm(2), where the variation in the relative transmission efficiency and in the center wavelength was less than 10% and 2 nm respectively. Finally, the influence of the angle of the incident beam upon the transfer characteristics of the device was investigated to reveal that the rate of change in the relative transmission was equivalent to about 1.5%/degree.

Fabrication of a nano-wire grid polarizer for brightness enhancement in liquid crystal display

The brightness enhancement of liquid crystal displays (LCD) through polarization recycling was investigated by placing a nano-wire grid polarizer (NWGP) between an LCD panel and a backlight unit. NWGPs with a period of 200 nm were fabricated using laser interference lithography and oblique deposition of aluminium. We optimized the fabrication process and achieved a high transmission of above 90% and a contrast ratio of above 12.5 for the range of wavelengths corresponding to visible light. This condition led to a strong enhancement of the brightness in an LCD with NWGP, which was 1.3 times higher than that without NWGP.

Application of nanoimprint lithography to nano-optics: wire grid polarizer and photonic crystal LED

Two optical devices with nano-scale subwavelength structures have been fabricated by using nanoimprint lithography (NIL). (1) Wire grid polarizer (WGP) is one of key optical components for projection displays with liquid crystal micro-display. Although WGP with 140 nm pitch is commercially available now, it still poses a problem with low extinction ratio (ER) for blue color. Since the ER can be increased by reducing the pitch, fabrication of a WGP with 100 nm pitch was attempted by NIL. We successfully developed thermal nanoimprint and aluminum dry etching processes. Fabricated WGPs showed twice higher ER than 140 nm pitch one. (2) Photonic crystal (PC) structures on LED have been known to enhance the light extraction significantly. Although e-beam lithography has been used for the proof of principle, it is far from real production method. We applied thermal NIL to fabricate PC structures in p-GaN layer of green LED. To identify the PC effect, two structures were fabricated and compared. One structure makes the green light of 525 nm wavelength fall within the photonic band gap (PBG) while the other puts it outside of PBG. The former structure showed 9-fold increment of photoluminescence compared to LED without PC structures, while the latter showed only 6-fold increment

Reliability test results of LGE pulse tube cryocooler

A low-cost and highly reliable cryocooler is strongly required for several applications. In this circumstance, LG Electronics has developed a 5 W at 65 K pulse tube cryocooler with high potential for low-cost manufacturing based on linear motor and compressor technology. Recently dozens of coolers have been fabricated and tested for the verification of performance stability with ambient temperature variation. From tests at high ambient temperature like 60°C, an average performance degradation of 45% is found and good performance stability of coolers is shown. Continuous operation at 40°C is ongoing for the verification of their reliability. To date no failure has been found. This paper discusses the test process, results and MTBF calculation.

Color Filter Based on a Sub-Wavelength Patterned Poly-Silicon Grating Fabricated using Laser Interference Lithography

A color filter was proposed and demonstrated by incorporating a subwavelength patterned 1-dimensional grating in poly silicon. It was produced by employing the laser interference lithography method, providing much wider effective area compared to the conventional e-beam lithography. A layer was introduced on top of the silicon grating layer as a mask for the etching of the silicon, facilitating the etching of the silicon layer. It was theoretically found that the selectivity of the filter was also improved thanks to the oxide layer. The parameters for the designed device include the grating pitch of 450 nm, the grating height of 100 nm and the oxide-layer height of 200 nm. As for the fabricated filter, the spectral pass band corresponded to the blue color centered at 470 nm and the peak transmission was about 40%. Within the effective area of , the variation in the relative transmission efficiency and in the center wavelength was less than 10% and 2 nm respectively. Finally, the influence of the angle of the incident beam upon the transfer characteristics of the device was investigated in terms of the rate of the relative transmission efficiency, which was found to be equivalent to 1.5%/degree.