Fabrication of Titanium Dioxide Thin Films by Dip Coating Process for Resistive Switching Applications

Abstract

Resistive switching devices have recently drawn enormous attention for the fabrication of next generation memory devices. Metal oxide thin films have drawn great deal of interest for memristor devices due to their CMOS compatibility. Titanium oxide (TiO2) is an excellent material for resistive switching applications because it is an insulating material, which consists of oxygen vacancies and has good thermal stability with high dielectric constant as well. TiO2 based resistive random-access memory (RRAM) devices have boosted up due to their higher writing speed and low operation power. In this research, TiO2 thin films are prepared by the sol-gel dip coating process with the optimized annealed temperature of 500 ºC. The morphological, structural characterizations of TiO2 thin films have been carried out by the Field Emission scanning electron microscope (FESEM, Nova Nano SEM 450), X-ray diffraction (XRD, Rigaku Ultima IV) and Raman spectroscopy techniques, respectively. The oxide and interface charge density of TiO2 thin films are estimated by capacitance-voltage measurements using Al/TiO2/Si metal oxide semiconductor (MOS) structures. The resistive switching behavior of TiO2 thin films are carried out using Al/TiO2/p++ Si metal insulator metal (MIM) structure. The switching operation has taken place by the formation and rupture of conductive filament, which is investigated further by estimating the current On/Off ratio. The films, coated with a withdrawal speed of 1 cm/min, have shown better resistive switching properties. The effects of different rapid thermal annealing process parameters on the resistive switching studies of TiO2 films are investigated. The resistive switching behavior is found to be varied with rapid thermal annealing (RTA) temperature, duration and ambient. For the improvement of resistive switching studies, structural modifications such as porous, thin film-nanorods hybrid structures, multilayer TiO2 films are synthesized. Porous TiO2 are synthesized using Pluronic F-127, thiourea additives with appropriate molar ratio. The film deposition for 8 % of thiourea has shown Set current with On/Off ratio of 1.4 × 105. The phase of the TiO2 film is found to be changed from anatase to rutile phase for high temperature annealing. The thin film-nanorods hybrid structures of TiO2 are fabricated with various nanorod growth parameters such as temperature and time and followed by dip coating at 1 cm/min to coat thin film layer on nanorods. The samples, grown at 180 ºC for 60 min, have shown improved resistive switching behavior. Thereafter, TiO2-ZnO multilayer films are synthesized in order to investigate the resistive switching behavior of ix the stack layers. The stack layers, synthesized with TiO2/ZnO/TiO2/TiO2 geometry, have shown Set current On/Off ratio of 1.45 × 104. The significant improvement in the current On/Off ratio has depicted the use of dip coated TiO2 films for futuristic low cost, high performance memory devices.