Atomic layer deposition of TiO2 thin film for biomedical applications

Abstract

Atomic Layer Deposition (ALD) is a bottom-up process for the manufacturing of inorganic nanostructured thin films, with thickness down to a fraction of a monolayer. Thanks to its unique mechanism of growth, ALD is a powerful technique that has achieved a lot of interest. In this work, a low pressure ALD process was employed to deposit titanium dioxide (TiO2) for biomedical neuro-chips applications based on electrolyte-oxide-semiconductor field-effect transistors (EOSFET). The aim was to optimize a custom-made ALD process for the deposition of high-k dielectric TiO2 starting from titanium tetra-isopropoxide and deionized water. Dense and pinhole-free thin films were deposited by working at controlled temperature (T<300°C) and by varying the process parameters. The structure-properties correlation of the grown thin films was studied by X-Ray Diffraction, Scanning Electron Microscopy, X-Ray Photoelectron Spectroscopy, Secondary Ion Mass Spectrometry and Ellipsometry. To evaluate the functional biomedical applications of TiO2 thin films via ALD, preliminary cellular-neuronal biocompatibility in-vitro tests were explored. Moreover, to study the influence on cell attachment/adhesion and growth, the surface chemical functionality was explored by wettability analyses by using Water Contact Angle (WCA). Next, to avoid a progressive atmospheric contamination, the hydrophilicity was restored exposing the samples by UV radiation and studying the WCA variation at different exposure times. Finally, further work will test neuronal in-vitro bioactivity by neurons deposition for a possible biomedical application, for the purpose of recording electrical activity and stimulating damaged brain areas.