Negative-tone block copolymer lithography by in situ surface chemical modification.

Negative-tone block copolymer (BCP) lithography based on in situ surface chemical modification is introduced as a highly efficient, versatile self-assembled nanopatterning. BCP blends films consisting of end-functionalized low molecular weight poly(styrene-ran-methyl methacrylate) and polystyrene-block-Poly(methyl methacylate) can produce surface vertical BCP nanodomains on various substrates without prior surface chemical treatment. Simple oxygen plasma treatment is employed to activate surface functional group formation at various substrates, where the end-functionalized polymers can be covalently bonded during the thermal annealing of BCP thin films.

Improved AlGaInP vertical emitting light-emitting diodes using direct printing.

In this study, we fabricated a high-brightness AlGaInP light-emitting diode (LED) using the direct printing technique and dry etching. In general, wet etching is used for surface roughening to improve the light extraction of AlGaInP red LEDs. However, a structure fabricated by wet etching has limited height and shows a tiled cone shape after the etching process due to the AlGaInP crystal structure.

Fabrication of SiNx-based photonic crystals on GaN-based LED devices with patterned sapphire substrate by nanoimprint lithography.

SiNx-based photonic crystal (PhC) patterns were fabricated on the ITO electrode layer of a GaN-based light-emitting diode (LED) device on a patterned sapphire substrate (PSS) by a UV nanoimprint lithography process in order to improve the light extraction of the device. A three-dimensional finite-difference time-domain simulation confirmed that the light extraction of a GaN LED structure on a PSS is enhanced when SiNx PhC patterns are formed on the ITO top layer. From the I-V characteristics, the electrical properties of patterned LED devices with SiNx-based PhC were not degraded compared to the unpatterned LED device, since plasma etching of the p-GaN or the ITO layers was not involved in the patterning process.

Improvement of photon extraction efficiency of GaN-based LED using micro and nano complex polymer structures.

A micro- and nanoscale complex structure made of a high refractive index polymer (n = 2.08) was formed on the ITO electrode layer of an edge-emitting type GaN blue light-emitting diode (LED), in order to improve the photon extraction efficiency by suppressing total internal reflection of photons. The nanoimprint lithography process was used to form the micro- and nanoscale complex structures, using a polymer resin with dispersed TiO2 nano-particles as an imprint resin.

Forming the graded-refractive-index antireflection layers on light-emitting diodes to enhance the light extraction.

Distributed antireflection (AR) layers with different composition ratios of ITO and SiO(2) formed on an ITO electrode of GaN-based LEDs provide substantial enhancement in light-extraction efficiency. By using the coradio frequency magnetron sputtering deposition, four 50 nm thick AR layers with graduated refractive indices were fabricated. The effect of the AR layers on enhancing the efficiency of the LED device was analyzed by electroluminescence (EL) and I-V measurements.

Fabrication of flexible UV nanoimprint mold with fluorinated polymer-coated PET film.

UV curing nanoimprint lithography is one of the most promising techniques for the fabrication of micro- to nano-sized patterns on various substrates with high throughput and a low production cost. The UV nanoimprint process requires a transparent template with micro- to nano-sized surface protrusions, having a low surface energy and good flexibility. Therefore, the development of low-cost, transparent, and flexible templates is essential.

The fabrication of a patterned ZnO nanorod array for high brightness LEDs.

In this study, a patterned ZnO nanorod array was formed on the ITO layer of GaN-based light-emitting diodes (LEDs), to increase the light extraction efficiency of the LED. The bi-layer imprinted resin pattern was used for selective growth of the ZnO nanorod array on the ITO layer. Compared to conventional LEDs grown on patterned sapphire substrate (PSS), the deposition of the blanket ZnO layer on the ITO layer increased the light extraction efficiency of the LED by about 10%.

Fabrication of 70 nm-sized zero residual polymer patterns by thermal nanoimprint lithography.

The formation of a residual layer under the imprinted patterns is commonly observed after the imprinting process. In order to utilize the imprinted patterns into the top-down process, the removal process of the residual layer using oxygen plasma is inevitable. However, the critical dimension of the imprinted patterns can be degraded during the residual layer removal process and this degradation becomes severer for smaller sized patterns.

Thermal imprinting of nano-patterns using thiol-based self-assembled monolayer-treated nickel template.

A highly durable imprint template is essential for the industrialization of nanoimprint lithography (NIL). Conventionally, Si-based materials were used for the fabrication of imprint templates. However, their fabrication is very expensive and they can be easily damaged during repeated imprint processes due to their brittleness and poor mechanical properties.

Insertion of two-dimensional photonic crystal pattern on p-GaN layer of GaN-based light-emitting diodes using bi-layer nanoimprint lithography.

Nanoimprint lithography (NIL) was adapted to fabricate two-dimensional (2-D) photonic crystal (PC) pattern on the p-GaN layer of InGaN/GaN multi quantum well light-emitting diodes (LEDs) structure to improve the light extraction efficiency. For the uniform transfer of the PC pattern, a bi-layer imprinting method with liquid phase resin was used. The p-GaN layer was patterned with a periodic array of holes by an inductively coupled plasma etching process, based on SiCl4/Ar plasmas.