The Regulation of VO2 Transition Temperature through Oxygen and Hydrogen Atom Control

Alternative Title
Minhwan Ko
Alternative Author(s)
Minhwan Ko
Hyungtak Seo
일반대학원 에너지시스템학과
The Graduate School, Ajou University
Publication Year
Alternative Abstract
Vanadium dioxide (VO2) is a typical Mott material having a metal-semiconductor transition at 341K, and many researches have been made because it can be used as a selector or transistor of next-generation memory. However, since the transition temperature is close to room temperature, switching reliability is low at the high temperature (i.e., > 341K) at which the device can easily reach during circuit operation so that desired characteristics cannot be obtained. To overcome this technical barrier, various studies have been conducted on the control of transition temperature in VO2 through impurity doping. The recent studies have been conducted using various elemental dopants such as W, Cr, Y, and Ti. However, studies on transition temperature changes through doping in thin film have some limitation that transition temperature varies according to the condition of thin film. In this study, we attempted to achieve a reliable transition temperature control in VO2. A VO2 nanobeam was synthesized by using VTC as a source of powder mixed with V2O5 and TiO2, and the ratio of TiO2 to V2O5 of the source powder was 0, 2, 4, 5, 10 at% Respectively. In addition, to solve the problem of the VTC method, the new VO2 nanobeam method of the DD method was devised and optimized. Then, the VO2 nanobeam fabricated using the DD method was doped with hydrogen using RIE plasma. The VO2 nanobeam formed through VTC and DD method identified the rectangular nanobeam shape through an optical microscope (OM) and the scanning electron microscope (SEM). The X-ray diffraction (XRD), transmission electron microscope (TEM), Energy-dispersive X-ray spectroscopy (EDS) and Secondary-ion mass spectrometry (SIMS) show that the phase and composition of the nanobeam are VO2 monoclinic. Finally, gold electrodes were deposited on both ends of the nanobeam to confirm the electrical characteristics and the transition temperature. It was confirmed that the transition temperature increased constantly as the Ti ratio of the source increased, reached the maximum value at 5 at%, and then decreased again. Since V 2p XPS spectra revealed the oxidation of V oxidation state, Ti precursor played a role in O supplier from surface V-O bonds as forming volatile Ti-O species. Therefore, this result implies that Ti reactants can be used as VO2 nanobeam surface chemical modifier to manipulate MIT transition temperature as maintaining homogenous VO2 phase, which is very useful for Mott device application. The distance dependence problem of the VTC method is solved by the DD method, and the VO2 nanobeam synthesized by the DD method is the same phase structure as the VO2 nanobeam synthesized by the VTC method, but the transition temperature is slightly increased due to the substrate did. Furthermore, hydrogen-doped VO2 nanobeam has been shown to be able to control the conductivity level at room temperature by controlling plasma power and time. This means that the transition temperature can be effectively controlled through the use of plasma-doped hydrogen and oxygen doping using a Ti reactant to use VO2 as a Mott device.

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Graduate School of Ajou University > Department of Energy Systems > 3. Theses(Master)
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