Epitaxial Growth and Stabilization of Perovskite Phase EuNiO ₃ Thin Films through Rf Sputtering

Abstract Phase change materials (PCMs) exhibiting volatile resistive switching can be implemented to emulate neuronal oscillators. Rare earth nickelates (ReNiO 3 , where Re = Pr, Nd, Sm, Eu…) are a family of PCMs whose metal‐insulator transition temperature (T MI ) can be tuned via chemical doping and/or strain engineering. EuNiO 3 is a particularly desirable choice, as its bulk TMI ∼190 °C, is sufficient to avoid the crosstalk issues for individual oscillators, yet low enough for promising low power applications. Here, we report a strategy to stabilize high‐quality epitaxial EuNiO 3 thin films using a scalable reactive RF sputtering process followed by post‐annealing treatment. Growth under low or zero oxygen partial pressure results in amorphous films, while high‐pressure growth improves crystallinity but stabilizes Ruddlesden‐Popper (RP) phases and corresponding faults. Post‐annealing improves the crystallinity in all the films and triggers the transformation of the RP phases/faults towards the desired perovskite phase. Operando X‐ray diffraction and transport measurements confirm that the perovskite films exhibit a transition at T MI = 315 °C and ∼225 °C for films grown on LAO and LSAT substrates, respectively. Structural and electronic characterization results indicate that epitaxial strain and oxygen vacancies are responsible for the enhancement of T MI observed in thin film.