Morphologic, structural, and optical characterization of sol-gel derived TiO2 thin films for memristive devices

Sol-gel derived TiO2 thin films were prepared by spin- coating from an alcoholic solution of titanium isopropoxide. With the aim to develop titania layers suitable for memristive devices, the films were deposited onto test structures based on fused silica quartz substrates patterned with a Ti (5nm)/Pt (50nm) layer. The reported fabrication protocol is suitable for the development of a memristive device. Optical, structural, and morphological features of the samples were investigated with complementary techniques, such as scanning electron microscopy (SEM), prism coupling m-line and micro-Raman spectroscopy as well as transmittance and profilometry measurements. The quality of the surface of the obtained films was evaluated by SEM technique, and the morphology of samples deposited with different fabrication protocols was investigated. Additionally, a computer code for the refractive index and thickness estimation from the transmittance spectra was developed by unconstrained optimization procedure. The results of simulation were in good agreement with the experimental data obtained by m-line measurements. Moreover, the porosity of a specific set of test unannealed films has been estimated. TiO2 films exhibit thickness of tens of nm, and micro-Raman spectroscopy in conjunction with SEM indicate the presence of anatase phase after thermal annealing at 400 °C. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)