Resistive switching in Pt/TiO$_{2}$/Pt

Recently, the resistive switching behavior in TiO$_{2}$ has drawn attention due to its application to resistive random access memory (RRAM) devices. TiO$_{2}$ shows characteristic non-volatile resistive switching behavior, i.e. reversible switching between a high resistance state (HRS) and a low resistance state (LRS). Both unipolar resistive switching (URS) and bipolar resistive switching (BRS) are found to be observed in TiO$_{2}$ depending on the compliance current for the electroforming. In this thesis the characteristic current-voltage (I-V) hysteresis in three different states of TiO$_{2}$, pristine, URS-activated, and BRS-activated states, was investigated and understood in terms of the migration of oxygen vacancies in TiO$_{2}$. The IV hysteresis of pristine TiO$_{2}$ was found to show volatile behavior. That is, the temporary variation of the resistance took place depending on the applied voltage. However, the I-V hysteresis of URS- and BRS-activated states showed non-volatile resistive switching behavior. Some evidences proving the evolution of oxygen gas during electroforming were obtained from time-of-flight secondary ion mass spectroscopy analysis and the variation of the morphology of switching cells induced by the electroforming. On the assumption that a large number of oxygen vacancies are introduced by the electroforming process, the I-V behavior in electroformed switching cells was simulated with varying the distribution of oxygen vacancies in electroformed TiO$_{x}$ (x $\lesssim$ 2). The I-V hysteresis undergoing the BRS was simulated with taking into consideration oxygen formation/annihilation reactions at a Pt/TiO$_{x}$ interface. The oxygen-related reactions given as a function of the applied voltage affect the distribution of oxygen vacancies in TiO$_{x}$, consequently, the Schottky barrier height at the cathode/TiO$_{x}$ interface is influenced by the oxygen vacancy distribution. Therefore, the BRS behavior including the electroforming characteristics could be understood in terms of the oxygen-related electrochemical reactions