Anodic TiO2 in ReRAM: Influence of Si-doping on the Resistive Switching Properties of Titanium Oxide

Abstract

TiO2 has attracted much attention due to its potential widespread applications, including capacitors, photocatalysis, solar energy conversion and, more recently, redox-based random access memories (ReRAM). For micro and nano-electronics applications, TiO2 is usually grown through Chemical and Physical Vapour Deposition techniques, such as Atomic Layer Deposition (ALD), Pulsed Laser Deposition (PLD), Sputtering and so on. In ReRAM field, the control of oxide structure (crystallinity, defects concentration etc.) and the choice of electrodes are crucial to have resistive switching phenomena inside the oxide. Thus, anodizing can be proposed as a simple and low cost way to grow TiO2 and to tune its structure, thickness and morphology by controlling substrate composition and oxidation conditions. Furthermore, it has been demonstrated that incorporation of foreign species, such as Si, during anodic titanium oxide growth can suppress field crystallization [1], modify solid state properties (dielectric constant, band gap etc. [2]) and, thus, change defects concentration and distribution inside TiO2. In this work we want to study the occurrence of resistive switching phenomena in anodic films grown on Ti and Ti-17at.%Si to 5 V (Ag/AgCl) in 1 M H3PO4. Photoelectrochemical measurements were performed in order to estimate band gap, flat band potential and conductivity type of the films as a function of growing conditions, while information of the dielectric constant of the oxides were obtained by impedance and differential capacitance measurements. The experimental results showed that incorporation of silicon in TiO2 has no significant effect on the band gap of the oxide, which resulted very close to that usually measured for amorphous anodic titanium oxide. On the other hand, a significant effect of silicon was evidence on dielectric constant of the anodic films which resulted to be sensitively lower than that of anodic TiO2. Quasi static current-voltage measurements were carried out to verify the presence of resistive switching phenomena into both the oxides, i.e. if the resistance of the twoterminal element (Metal/Anodic film/Pt) changes under application of an external electric field between two stable states, a high-resistive state (HRS) and a low-resistive state (LRS). Durability tests were also carried out to assess the possible use of this device as ReRAM. The obtained results were rationalized taking into account the effect of anodizing conditions and Si incorporation on the amorphosity and stoichiometry of TiO2. References [1] H. Habazaki, et. al., Corr. Sci., 45, (2003), 2063. [2] F. Di Quarto, et. al., , Electrochim. Acta, 110, (2013), 157.