Relationships between elaboration conditions, structural parameters and electrical properties in metal oxides nanometric periodic multilayers

Abstract

Ti/TiOx and W/WOx multilayered thin films have been deposited by DC reactive sputtering using the reactive gas pulsing process (RGPP). It is implemented to produce regular alternations of metal‐oxide compounds at the nanometric scale [1, 2]. Structure and growth have been investigated by High Resolution Transmission Electron Microscopy (HRTEM), Scanning Transmission Electron Microscopy (STEM) Energy Dispersive X‐rays Spectroscopy (EDX) and Energy Electron Loss Spectroscopy (EELS). Regularity of titanium and tungsten based alternations, quality of interfaces as well as oxygen diffusion through the multilayered structure have been examined taking into account the reactivity of oxygen towards the metals. Electrical measurements have been also carried out with the van der Pauw method to determine resistivity changes with temperature. CTEM has been performed to determine the thickness of the periodic metallic and oxide layers from 3 to 40 nm. HRTEM experiments have been carried out to study the atomic structure of the periodic layers. The study of HRTEM images has allowed determining a growth model with the following series: (rutile‐)TiO 2 , fcc‐TiO and α‐Ti for Titanium system. This result has been confirmed by SAED experiments. Chemical information was obtained from the core‐loss EELS and EDX spectra. Core‐loss study was particularly performed for TiOx samples to quantify the elemental composition from the Ti‐L 2,3 and O‐K edges (Fig. 1). The systematic presence of oxygen has been pointed out in the rich‐metal sub‐layer, corresponding to the TiO phase already pointed out by HRTEM. Concerning tungsten system, the layers appear to be mainly amorphous. Therefore, low‐loss EELS study was performed and has allowed determining a growth model with the following series: W/W 3 O/WO 3 /W 3 O (Fig. 2). The knowledge of the structural parameters has allowed determining a first relation between the elaboration conditions (control of the pressure value) and the structural parameters. Electrical and structural results have also been related to propose a law linking the resistivity values ρ to the structural parameters as total thickness e tot , metal λ met and oxide λ ox layers thickness and metal elemental composition C met (Fig. 3).