Hydrothermal Growth Of TiO₂Films And The Resistive Switching Properties

With the development of the semiconductor industry, the unit size of the storage device isreducing. Memristor shows superiority in high storage capacity, small size, high-speed, lowenergy consumption characteristics, and is expected to replace the transistor to become newtype storage devices. Due to its good physical and chemical stability, TiO2thin film haspotential applicaition in memristor devices. In the present study, TiO2films were preparedwith a hydrothermal synthesis method, the RRAM properties of the memristors made of TiO2film were investigated, and the resistance switching mechanisms were analyzed.In this work, TiO2thin films were synthesized from a novel F--containing solution, and asol-gel TiO2seed layer was introduced during the growth. The effect of the solutioncomposition, seed layer, growth temperature and time on the morphologies, structure and theRRAM properties were explored. By comparing the RRAM properties of the growth TiO2film and the sol-gel TiO2films, the the resistance switching mechanisms of TiO2films werestudied.The experimental results demonstrate that, preheating the growth solution improves thesaturation of TiFx(OH)4-xhydrolyzed from the precursor species TiF62-, which prevents theetching of TiO2seed lay by the solution. The thickness of one single lay of TiO2seed is about20-30nm, the thichness of TiO2film grown for3h is about100nm, and the films are highlyoriented in (004) direction. The seed layer provides the active points for the formation of thecrystal nuclei, which helps to improve the density of the film. The strong bonding strength ofF-to Ti can reduce the hydrolyzation rate of the precursor species as well as the crystal facetenergy. The slow hydrolyzation rate improves the crystallinity of TiO2film, the lower energyof (001) facet and the selective dehydration of Ti complexing species support the orientationgrowth of TiO2film.The research results on the RRAM properties of TiO2film show that, the memoristor unitmade of of TiO2film of the poor density produced the large electricity leakage, and the on/offratio is reduced. Increasing the film thickness can increase the on/off voltage, and the energyconsumption is also increased. The oriented structure of TiO2film provides the diffusion channel for the charging carriers of the memoristor units, which reduces the diffusion energybarrier and the on/off voltage of the film. The TiO2memoristor with the low-work-functiontop electrode shows good switching property but the TiO2memoristor with high-work-fuctiontop electrode gives only the Schottky contact characteristcs. Based these conclusions, thecharging carrier diffusition mechanisms can be deduced.Further experimental results suggest that, with the similar thickness, compared to therandom TiO2film prepared with the sol-gel technology, the (001)-oriented TiO2film showslarge resistance on/off ratio, low on/off voltage, and good RRAM stablility. The RRAMproperites are improved with the enhanced orientation of the film. Compared to the FTOsubstrate, the surface of the Pt substrate is much smoother, on which the density and theoriention are improved. Correspondingly, the on/off voltage of the memoristors on the Ptsubstrate is decreased, the stability is better, and the problems caused by the structural defectsrelated to the nonuniform of the film thicknes are weakened.