Evaluation of Chemical Structure and Resistance Switching Characteristics of Undoped Titanium Oxide and Titanium–Yttrium Mixed Oxide

Abstract

We have studied the chemical bonding features in the region near the TiO2/Pt interface after resistance change to gain a better understanding of the mechanism of resistance switching in TiO2-based resistance random access memory (ReRAM). For the Pt/TiO2/Pt structure after resistance switching, oxidation of the Pt electrode at the Pt/TiO2 interface in switching from a high resistance state (HRS) to a low resistance state (LRS) and reduction of this Pt-oxide in switching from the LRS to the HRS were observed by hard X-ray photoelectron spectroscopy. The result suggests that the generation of oxygen vacancies in the Ti-oxide matrix is responsible for the formation of the conductive pass resulting in the LRS and that repeatable redox reaction at the Pt/TiO2 interface plays an important role in resistance switching behavior. To modify the oxide network, which leads to the change in the conduction pass formation, trivalent Y ions were added to the oxide matrix of quadrivalent Ti ions. Raman scattering and X-ray diffraction measurements show that the crystallization of TiO2 by thermal annealing was suppressed by the Y2O3 addition. In Au/TiYxOy/Pt structures, it has been demonstrated that the variations in resistance switching voltages are markedly suppressed by the Y2O3 addition to TiO2.