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

TiO2 has attracted much attention due to its potential widespread applications, includingcapacitors, photocatalysis, solar energy conversion and, more recently, redox-basedrandom access memories (ReRAM). For micro and nano-electronics applications, TiO2is usually grown through Chemical and Physical Vapour Deposition techniques, such asAtomic 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 insidethe oxide. Thus, anodizing can be proposed as a simple and low cost way to grow TiO2and to tune its structure, thickness and morphology by controlling substrate compositionand oxidation conditions. Furthermore, it has been demonstrated that incorporation offoreign species, such as Si, during anodic titanium oxide growth can suppress fieldcrystallization [1], modify solid state properties (dielectric constant, band gap etc. [2])and, thus, change defects concentration and distribution inside TiO2. In this work wewant to study the occurrence of resistive switching phenomena in anodic films grownon Ti and Ti-17at.%Si to 5 V (Ag/AgCl) in 1 M H3PO4. Photoelectrochemicalmeasurements were performed in order to estimate band gap, flat band potential andconductivity type of the films as a function of growing conditions, while information ofthe dielectric constant of the oxides were obtained by impedance and differentialcapacitance measurements. The experimental results showed that incorporation ofsilicon in TiO2 has no significant effect on the band gap of the oxide, which resultedvery close to that usually measured for amorphous anodic titanium oxide. On the otherhand, a significant effect of silicon was evidence on dielectric constant of the anodicfilms which resulted to be sensitively lower than that of anodic TiO2.Quasi static current-voltage measurements were carried out to verify the presence ofresistive switching phenomena into both the oxides, i.e. if the resistance of the twoterminalelement (Metal/Anodic film/Pt) changes under application of an externalelectric field between two stable states, a high-resistive state (HRS) and a low-resistivestate (LRS). Durability tests were also carried out to assess the possible use of thisdevice as ReRAM. The obtained results were rationalized taking into account the effectof anodizing conditions and Si incorporation on the amorphosity and stoichiometry ofTiO2.References[1] H. Habazaki, et. al., Corr. Sci., 45, (2003), 2063.[2] F. Di Quarto, et. al., , Electrochim. Acta, 110, (2013), 157.