Understanding phase evolution of ferroelectric Hf 0.5 Zr 0.5 O 2 thin films with Al 2 O 3 and Y 2 O 3 inserted layers

This study investigates the insertion traits of the Al 2 O 3 and Y 2 O 3 insertion layers (ILs) and their effects on the phase evolution and electrical characteristics of polycrystalline Hf 0.5 Zr 0.5 O 2 (HZO) thin films grown by atomic layer deposition (ALD). The Al 2 O 3 and Y 2 O 3 ILs are located at the middle position along the HZO film. The thick Al 2 O 3 IL, above 2–3 ALD cycles, forms a continuous layer, physically separating the upper and lower regions of the film. Conversely, the thin Al 2 O 3 IL, below 2–3 ALD cycles, and all the Y 2 O 3 IL diffuse into the nearby HZO layers, making a single Al- or Y-doped HZO layer. The most crucial finding is that the diffused trivalent Al and Y ions substitute the tetravalent Hf and Zr ions, creating oxygen vacancies for charge neutrality and changing the phase evolutions. The substituted Al and Y suppress the monoclinic phase and enhance the tetragonal phase. Ultimately, the study suggests a new perspective on doped HfO 2 -based thin films, highlighting the crucial role of substitutional diffusion of dopants and charge neutrality in determining the formation of the tetragonal phase.