Mandal B., Valle N., Adib B.E., Girod S., Menguelti K., Fleming Y., Grysan P., Defay E., Glinsek S.
Advanced Electronic Materials, vol. 10, n° 8, art. no. 2300893, 2024
Chemical Solution Deposition enables low-cost fabrication of ferroelectric HfO<sub>2</sub> films suitable for piezoelectric applications. Control of processing parameters is of utmost importance to obtain high-quality functional films. However, the impact of the annealing atmosphere on ferroelectric properties of solution-processed HfO<sub>2</sub> films is not clear. In this work, the influence of annealing atmosphere and growth methods on orientation, density and electrical properties of La:HfO<sub>2</sub> films is studied. The 45 nm-thick films are grown by two routes, conventional (crystallization of the final 45 nm-thick film) and layer-by-layer (intermediate crystallizations of 5 nm-thick films). Annealing is performed in N<sub>2</sub>:O<sub>2</sub> and Ar atmosphere. Films grown by layer-by-layer method in an oxygen-rich atmosphere tend to have higher density (87% of theoretical density) and remanent polarization (15 µC cm<sup>–2</sup>) than the conventional films (density and remanent polarization of 80% and 7.5 µC cm<sup>-2</sup>). Secondary ion mass spectrometry reveals higher amounts of carbon presence in the conventional films annealed in Ar. For layer-by-layer films, the ability to control the preferential out-of-plane orientation from (111) to (002) simply by changing the annealing atmosphere, is demonstrated. The results can guide the path toward high-quality thicker films for piezoelectric applications.
