Titre de la dissertation: « Process-Plasma-Material Properties Relationship in the Deposition of Bismuth Sodium Titanate Thin Films by Magnetron Sputtering ».

Promoteurs de thèse: Monsieur Stéphanos Konstantinidis et Monsieur Damien Remiens (UPHF)

Résumé de la dissertation: This work is dedicated to the synthesis and characterization of ferroelectric piezoelectric Bi_0.5Na_0.5TiO₃ (BNT) thin films. The films were deposited on Si substrates using homemade powder targets by RF magnetron sputtering in an Ar discharge. The target surface analysis, plasma diagnostics, and film characterization were performed, alongside modelling of sputtering and gas-phase transport processes, to understand the correlation between the target-plasma-film chemistry. To optimize the composition of BNT films, the influence of parameters like the target composition, sputtering power density, and target–substrate distance was investigated for addressing the challenges such as excess deposition of Bi during film growth and sublimation-driven Na loss during the annealing of films. This led to the realization of deposition protocol for stoichiometric and highly crystallized BNT films, grown on unheated substrates. To study the root-causes of NaO_x surface defects formation on BNT films, the effect of target composition on the ionized part of deposition flux was investigated. A sublimation process for Na atoms was identified, concurrently occurring on the target surface alongside the sputtering, which is likely linked to the growth of NaO_x surface defects on BNT films.

Lieu de défense: UPHF de Valenciennes