Byeong Ju Bae

Fabrication of Moth-Eye Structure on Glass by Ultraviolet Imprinting Process with Polymer Template

An antireflection moth-eye structure was fabricated on a glass substrate by ultraviolet nanoimprint lithography (UV-NIL). A Ni template with an artificial conical structure was fabricated by laser interference lithography an used as a stamp for embossing. A transparent PVC template was fabricated by hot embossing. The embossed poly(vinyl chloride) (PVC) film was then used as an imprint template after depositing SiO2 and a self-assembled monolayer (SAM). Using the embossed PVC film as a UV-NIL stamp, a polymer based moth-eye structure was formed on the glass template and its transmittance, parallel to surface normal, was increased to 93% for a single side patterned and 97% for a double side patterned. However, at wavelengths shorter than 430 nm, the transmittance of 30°-rotated glass substrate with a moth-eye structure became lower than that of the bare glass substrate, while the transmittance was not changed for longer wavelength regions.

Fast switching behavior of nanoscale Ag6In5Sb59Te30 based nanopillar type phase change memory

Ag and In co-doped SbTe phase change material (AgInSbTe) was used to fabricate nanopillar phase change memory. The AgInSbTe nanopillar type phase change device with 200 nm of diameter was fabricated by nanoimprint lithography and was reversibly changed between the resistances of 10(4) and 10(6) Omega by applying set/reset pulses using conducting atomic force microscopy. Due to the fast crystallization nature of AgInSbTe, the set operation of the device could be done with only 50 ns of set pulse. The fast crystallization nature of AgInSbTe is also responsible for the decrease in reset voltage of devices set with a short pulse.

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...

Spectromicroscopic investigation of lateral-type Ge2Sb2Te5 device failure

Scanning photoelectron microscopy with synchrotron radiation was used to investigate the failure phenomena of phase-change memory devices based on the Ge2Sb2Te5 (GST) system with a native oxygen impurity. The scanning photoelectron microscopy (SPEM) images and spectra obtained on the surface of the SET-failed device showed that many of the Sb atoms as well as some of the Ge atoms had diffused toward the region far away from the Mo electrodes. On the other hand, most of the Te atoms remained in the middle part of the GST. This suggests that device failure resulted in the out-diffusion of Sb atoms through SET and RESET processing, especially on the surface. The remaining GST system with less Sb was suggested to be one of the causes of the failure of the phase transition by SET and RESET.

Fabrication of Moth-Eye Pattern on a Lens Using Nano Imprint Lithography and PVA Template

Antireflection pattern, moth-eye structure, was fabricated on lens using Ultra Violet nanoimprint lithography and flexible template. Ni template with conical shaped structure was used as a master template to molding. The flexible poly vinyl alcohol template was fabricated by molding. This poly vinyl alcohol template was used as an imprint template of imprint at lens. Using Ultra Violet nanoimprint lithography and poly vinyl alcohol template, polymer based moth-eye structure was formed on lens and its transmittance was increased up to 94% from 92% at 550 nm wavelength.

Fabrication and Evaluation of Nanopillar-Shaped Phase-Change Memory Devices

In this study, nanopillar-shaped phase-change memory devices of various sizes were simply fabricated by nanosphere lithography, and their electrical characteristics were evaluated by conductive atomic force microscopy (AFM). As nanosphere materials, 180-nm diameter polystyrene balls were used for a size-controllable mask, silica balls with a diameter of 200 nm for a high etching-resistance mask, and sub-50 nm Ag nanoparticles were used for sub-50-nm-scale fabrication. Using the polystyrene balls, silica balls, and Ag nanoparticles, nanopillar-shaped phase-change memory devices with various diameters, heights as large as 1 µm, and sizes as small as less than 50 nm were successfully fabricated. The electrical properties of the nanopillar-shaped Ge2Sb2Te5 devices were evaluated by conductive AFM with an electrical measurement system.

Glass Substrate with UV Imprinted Polymer Moth Eye Structure

Artificial polycarbonate moth eye structured plate was used to emboss the moth eye nano-pattern into PVC films. Embossing was done at 100°C to prevent any damage on polycarbonate template. With embossing of moth eye nano-patterns, transmittance of PVC film was increased up to 6% over 400nm to 800nm wavelength region. This embossed PVC film was then used as an imprint template after depositing thin layer of SiO2 and self-assembled monolayer. Consequently, polymer based moth eye nano-patterns were formed on glass template after UV imprinting and its transmittance was increased from 90% to 92%.