Yong Jai Cho

In situ control of oxygen vacancies in TiO 2 by atomic layer deposition for resistive switching devices

Oxygen vacancies (V(O)) have profound effects on the physical and chemical performance of devices based on oxide materials. This is particularly true in the case of oxide-based resistive random access memories, in which memory switching operation under an external electrical stimulus is closely associated with the migration and ordering of the oxygen vacancies in the oxide material. In this paper, we report on a reliable approach to in situ control of the oxygen vacancies in TiOx films. Our strategy for tight control of the oxygen vacancy is based on the utilization of plasma-enhanced atomic layer deposition of titanium oxide under precisely regulated decomposition of the precursor molecules (titanium (IV) tetraisopropoxide, Ti[OCH(CH₃)₂]₄) by plasma-activated reactant mixture (N₂+O₂). From the various spectroscopic and microstructural analyses by using Rutherford backscattering spectrometry, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, confocal Raman spectroscopy, and spectroscopic ellipsometry, we found that the precursor decomposition power (R(F)) of plasma-activated reactant mixture determines not only the oxygen vacancy concentration but also the crystallinity of the resulting TiO(x) film: nanocrystalline anatase TiO(x) with fewer oxygen vacancies under high R(F), while amorphous TiOx with more oxygen vacancies under low RF. Enabled by our controlling capability over the oxygen vacancy concentration, we were able to thoroughly elucidate the effect of oxygen vacancies on the resistive switching behavior of TiO(x)-based memory capacitors (Pt/TiO(x)/Pt). The electrical conduction behavior at the high resistance state could be explained within the framework of the trap-controlled space-charge-limited conduction with two characteristic transition voltages. One is the voltage (V(SCL)) for the transition from Ohmic conduction to space-charge-limited conduction, and the other is the voltage (V(TFL)) for transition from space-charge-limited conduction to trap-filled-limited conduction. In this work, we have disclosed for the first time the dependence of these two characteristic transition voltages (i.e., V(SCL) and V(TFL)) on the oxygen vacancy concentration.

3-D Surface Profile Measurement Using An Acousto-optic Tunable Filter Based Spectral Phase Shifting Technique

An acousto-optic tunable filter based 3-D micro surface profile measurement using an equally spaced 5 spectral phase shifting is described. The 5-bucket spectral phase shifting method is compared with a Fourier-transform method in the spectral domain. It can provide a fast measurement capability while maintaining high accuracy since it needs only 5 pieces of spectrally phase shifted imaging data and a simple calculation in comparison with the Fourier transform method that requires full wavelength scanning data and relatively complicated computation. The 3-D profile data of micro objects can be obtained in a few seconds with an accuracy of

Surface Form Measurement Using Single Shot Off-axis Fizeau Interferometry

{\sim}10nm

Ellipsometric examination of optical property of the Si–SiO2 interface using the s-wave antireflection

. The 3-D profile method also has an inherent benefit in terms of being speckle-free in measuring diffuse micro objects by employing an incoherent light source. Those simplicity and practical applicability is expected to have diverse applications in 3-D micro profilometry such as semiconductors and micro-biology.

Snapshot phase sensitive scatterometry based on double-channel spectral carrier frequency concept.

This paper describes the surface form measurement of a spherical smooth surface by using single shot off-axis Fizeau interferometry. The demodulated phase map is obtained and unwrapped to remove the

Angle-resolved annular data acquisition method for microellipsometry

2\pi

Enhancement of biomolecular detection sensitivity by surface plasmon resonance ellipsometry

ambiguity. The unwrapped phase map is converted to height and the 3D surface height of the surface object is reconstructed. The results extracted from the single shot off-axis geometry are compared with the results extracted from four-frame phase shifting in-line interferometry, and the results are in excellent agreement.

Ultrasensitive, label-free detection of cardiac biomarkers with optical SIS sensor

Using variable-angle spectroscopic ellipsometry and introducing two models (a three-phase and a two-film model), we examined the optical properties of thermally grown SiO2 layers on Si, with special focus on phase difference Δ and amplitude ratio tan ψ for the s and p waves. We found an abrupt flip of the cos Δ curve from which the s and p-wave antireflection conditions were determined and evaluated the interface sensitivities for cos Δ and tan ψ based on the three-phase (ambient-oxide substrate) and the two-film (ambient-oxide-interlayer substrate) model. The sensitivities for cos Δ and tan ψ were shown to have maximum values at the same angle of incidence and photon energy in the s-wave antireflection condition. By fitting the variable-angle spectroscopic ellipsometry data measured in the s-wave antireflection condition, the thickness of the Si–SiO2 interface was determined as 0.784±0.003 nm for a 52-nm thick oxide sample and 0.764±0.002 nm for a 150-nm-thick oxide one. We also found that the effective ...

A new spectral imaging ellipsometer for measuring the thickness of patterned thin films

Spectroscopic ellipsometry is one of the most important measurement schemes used in the optical nano-metrology for not only thin film measurement but also nano pattern 3D structure measurement. In this paper, we propose a novel snap shot phase sensitive normal incidence spectroscopic ellipsometic scheme based on a double-channel spectral carrier frequency concept. The proposed method can provide both Ψ(λ) and Δ(λ) only by using two spectra acquired simultaneously through the double spectroscopic channels. We show that the proposed scheme works well experimentally by measuring a binary grating with nano size 3D structure. We claim that the proposed scheme can provide a snapshot spectroscopic ellipsometric parameter measurement capability with moderate accuracy.

Optical characterization of silicon dioxide layers grown on silicon under different growth conditions

An ellipsometric data acquisition method is introduced to measure the optical properties of sample. It is based on a microellipsometer hardware layout integrated a high numerical aperture objective lens, which is aligned in the normal direction of sample surface. This technique enables to achieve ellipsometric data at multiple incident angle with a sub-mum probe beam size, moreover real-time measurement is possible due to no moving parts. The experimental results of different SiO(2) thin film are demonstrated, also calibration technique is described.