Seon Yong Hwang

Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography

The fabrication process of photonic crystals in a p‐GaN layer was established to improve the light extraction efficiency of light-emitting diodes (LEDs) by using nanoimprint lithography and inductively coupled plasma (ICP) etching process. Due to low etch selectivity of imprinted pattern, Cr mask patterns were lifted-off from the p‐GaN surface and ICP etch process was followed using SiCl4-based plasma. As a result, two-dimensional pillar array patterns were uniformly fabricated on the p‐GaN layer and the photoluminescence intensity of the photonic crystal patterned LED was increased by 2.6 fold compared to that of the same LED sample without photonic crystal patterns.

Electrical characterization of Ge-Sb-Te phase change nano-pillars using conductive atomic force microscopy

The electrical characteristic of phase change material was studied in nano-scale using nanoimprint lithography and a conducting atomic force microscopy measurement system. Nanoimprint lithography was used to fabricate the nano-scale phase change material pattern. A Pt-coated AFM tip was used as a top electrode to measure the electrical characteristics of the GST nano-pillar. The GST nano-pillar, which is 200 nm in diameter, was amorphized by 2 V and 5 ns reset pulse and was then brought back to the crystalline phase by applying 1.3 V and 150 ns set pulse. Using this measurement system, the GST nano-pillar was switched between the amorphous and crystalline phases more than five times. The results of the reset and the set current measurement with the GST nano-pillar sizes show that the reset and the set currents also decreased with the decrease of the GST pillar size.

Lift-off process using bilayer ultraviolet nanoimprint lithography and methacryloxypropyl-terminated-polydimethylsiloxane-based imprint resin

A high-fidelity lift-off process using bilayer ultraviolet nanoimprint lithography (UV-NIL) to fabricate nanosized metal pattern was demonstrated. High O2 reactive ion etching (RIE) selectivity of the imprinted resist pattern to the underlayer is necessary to create the undercut pattern profile that is essential for the stable lift-off process. A methacryloxypropyl-terminated polydimethylsiloxane (M-PDMS)-based UV-curable liquid-phase imprint resin and a polyvinyl alcohol (PVA) underlayer were applied to bilayer UV-NIL for the high-fidelity lift-off process. The M-PDMS-based imprinted resist pattern showed high etch resistance to O2 plasma and the undercut pattern profile of the PVA underlayer for the lift-off process was formed by the O2 RIE process. The size and shape of the imprinted resist patterns were hardly changed during PVA underlayer etching by O2 RIE. As a result, high-fidelity and high-aspect-ratio metal patterns without rabbit-ear-shaped defects were fabricated by the lift-off process using b...

Enhanced light extraction of light-emitting diodes with photonic crystal pattern fabricated by nanoimprint

A hexagonal array of sub-micron sized holes was fabricated on InGaN/GaN quantum-well light-emitting diodes using nanoimprint lithography. Photoluminescence measurement confirms that light extraction of the LED was enhanced with two-dimensional photonic crystal patterns.

Fabrication of photonic crystal-patterned light emitting diodes using nanoimprint lithography

This work reports on the economical and effective fabrication process of photonic crystal patterns on GaN-based light emitting diode (LED) structures using nanoimprint lithography (NIL) and inductively coupled plasma (ICP) etching process. Results reveal the capability of using NIL to fabricate sub-micron sized, photonic crystal patterns at reduced cost for high brightness LEDs.