Ferroelectricity Induced by Oxygen Vacancies in Rhombohedral <scp>ZrO<sub>2</sub></scp> Thin Films
Veniero Lenzi, José Silva, Břetislav Šmíd, Vladimı́r Matolín, Marian Cosmin Istrate, Corneliu Ghica, Judith L. MacManus‐Driscoll, L. Marques
Abstract
Rhombohedral phase Hf x Zr 1‐ x O 2 (HZO, x from 0 to 1) films are promising for achieving robust ferroelectric polarization without the need for an initial wake‐up pre‐cycling, as is normally the case for the more commonly studied orthorhombic phase. However, a large spontaneous polarization observed in rhombohedral films is not fully understood, and there are also large discrepancies between experimental and theoretical predictions. In this work, in rhombohedral ZrO 2 thin films, we show that oxygen vacancies are not only a key factor for stabilizing the phase, but they are also a source of ferroelectric polarization in the films. This is shown experimentally through the investigation of the structural properties, chemical composition and the ferroelectric properties of the films before and after an annealing at moderate temperature (400 °C) in an oxygen environment to reduce the V O concentration compared. The experimental work is supported by density functional theory (DFT) calculations which show that the rhombohedral phase is the most stable one in highly oxygen defective ZrO 2 films. The DFT calculations also show that V O contribute to the ferroelectric polarization. Our findings reveal the importance of V O for stabilizing rhombohedral ZrO 2 thin films with superior ferroelectric properties.