Does a Morphotropic Phase Boundary Exist in Zr _x Hf _1‐x O ₂ ‐Based Thin Films?

Abstract Zr _x Hf _1‐x O ₂ ‐based materials have attracted considerable interest due to their excellent scalability and compatibility with complementary metal‐oxide‐semiconductor technology. Following the discovery of ferroelectricity in these materials, it has opened new avenues not only redefining ferroelectric memory but also as a promising high‐k dielectric for advanced non‐volatile and volatile memory applications by utilizing specific crystalline phases to tune the electrical parameters. Various fundamental factors influencing the formation of ferroelectricity in Zr _x Hf _1‐x O ₂ have been identified and distinguished from those in the classical perovskite ferroelectrics. Notably, a sharp increase in the dielectric constant near 0 V observed in Zr‐rich Zr _x Hf _1‐x O ₂ films achieved by tuning the fabrication parameters has been attributed to the presence of a morphotropic phase boundary. This study investigates 6 nm Zr‐rich Zr _x Hf _1‐x O ₂ thin film metal‐insulator‐metal capacitors using a combination of experimental methods and machine learning‐based molecular dynamics simulations. The study provides insight into the physical mechanisms that enhance the dielectric constant near 0 V and attributes it to the orthorhombic phase rather than a morphotropic phase boundary. The work discusses the limitations in the practical application of the high dielectric constant observed near 0 V. Additionally, it highlights similarities and differences between Zr _x Hf _1‐x O ₂ and the well‐known morphotropic phase boundary in PbZr _x Ti _1‐x O ₃ .