Sang Jun Kim

Study of Oxygen-Doped GeSbTe Film and Its Effect as an Interface Layer on the Recording Properties in the Blue Wavelength

An oxygen-doped GeSbTe interface layer improves the overwriting characteristics of the phase-change optical disk in the blue wavelength. The thermal and optical properties of oxygen-doped GeSbTe film and its crystal structure were investigated. Crystallization temperature and activation energy of the amorphous Ge–Sb–Te–O films are increased with the oxygen concentration while the melting point is decreased. The refractive index of the crystalline state monotonically increases with the oxygen concentration of the film, while its extinction coefficient monotonically decreases. In terms of the crystalline structure, fcc characteristic peaks disappear gradually with oxygen concentration, and above 35 at.% of oxygen, hexagonal peaks appear.

Enhanced Readout Signal of Elliptic-Bubble Super Resolution Near Field Structure by Temperature-Dependent Complex Refractive Index of Phase-Change Medium

We propose a model elucidating the readout mechanism of the super resolution near-field structure (super-RENS) with an elliptic-bubble structure. The temperature dependence of the complex refractive index of Ge2Sb2Te5 is determined by in situ ellipsometry. The complex refractive index of Ge2Sb2Te5 shows quite an abrupt change at approximately 608°C. The temperature profile is calculated using a proposed first-order differential equation. Above the threshold readout power, Ge2Sb2Te5 is locally heated over the critical temperature when thickest region of Ge2Sb2Te5 is in commensurate with the center position of the Gaussian laser power distribution, which results in the abrupt amplification of signal-to-noise ratio (SNR) of the calculated reflectance. Thus, a model revealing the essential aspect of the elliptic-bubble super-RENS is proposed to elucidate its readout mechanism.

Experimental Setup for in Situ Investigation of Phase Changing Behavior in Phase-Change Random-Access Memory Medium by Microfocusing Nanosecond-Time-Resolved Ellipsometry

An ellipsometer with nanosecond time resolution has been proposed for the investigation of the phase change behavior of Ge2Sb2Te5 heated by electrical pulses of 20–100 ns in real time. This passive single-wavelength ellipsometer has a division-of-amplitude photopolarimeter (DOAP) configuration for polarization state detection to collect ellipsometric data in nanoseconds and consists of a microfocusing lens system to achieve a spot size of ~15 µm.

Study of Ultra-Small Optical Anisotropy Profile of Rubbed Polyimide Film by using Transmission Ellipsometry

Anisotropy profile of a rubbed polyimide film is investigated using both a modified ultra high precision transmission ellipsometer and the analysis software previously developed to determine the optic axis distribution of discotic liquid crystals in the wide view film. The distorted sinusoidal variation of the ellipsometric constants obtained at an oblique angle of incidence indicates that the optic axis varies from

Ellipsometric Simulation and Preliminary Observation of Fast Crystallization Behavior of Ge2Sb2Te5 Amorphous Thin Films at Elevated Temperature

14.7^{\circ}

Irreversible Optical Properties of AgOx Mask Layer with Temperature for Super-Resolution Near-Field Structure Application Investigated by in situ, ex situ Ellipsometry

to

Enhanced Readout Signal of Elliptic Bubbled Super-RENS by Temperature Dependent Complex Refractive Index of Phase Change Medium

40.6^{\circ}

Experimental Setup for In situ Investigation of Phase Changing Behavior in Pram Medium by Micro-Focusing Nanosecond Time Resolved Ellipsometry

from the sample plane. The magnitude and distribution of anisotropy is expressed in terms of no, ne, and the cosine-shaped tilt angle distribution of the optic axis in a rubbed polyimide film.

Real-Time Growth Control of Ge–Sb–Te Multilayer Film as Optical Recording Media by In Situ Ellipsometry

We examine the fast crystallization kinetics of the stoichiometric Ge–Sb–Te alloy film by using a modified Johnson–Mehl–Avrami (JMA) equation and additive reaction for nonisothermal transformation. It is expected that utilization of the fast crystallization kinetics of the recording medium occurring at the first stage of cascaded crystallization will significantly reduce the erase time at elevated temperatures. We also show an ellipsometric configuration which enables one to confirm the fast crystallization kinetics in nanosecond time resolution.

Spectro-Ellipsometry Investigation of Cascaded Crystallization Behavior of Phase-Change Ge–Sb–Te Alloy

The optical properties of AgOx thin films used as mask layers for a super-resolution near-field structure (super-RENS) were determined by in situ and ex situ ellipsometries and UV/VIS spectrometry. Irreversible changes of optical properties of AgOx thin films with temperature were also investigated.