Improved ferroelectricity and endurance in Ca doped Hf0.5Zr0.5O2 films

Doped Hf_0.5Zr_0.5O₂ materials have drawn increasing attention due to the excellent ferroelectric properties, but the relevant research is just in the preliminary stage and the reported doped systems are rare. In this work, Ca doped Hf_0.5Zr_0.5O₂ (Ca:HZO) ferroelectric films were successfully fabricated via chemical solution deposition and investigated for the first time. It is observed that Ca doping induces a phase transformation from monoclinic to orthorhombic/tetragonal and then to monoclinic/tetragonal. The highest orthorhombic phase fraction is achieved in 2.5 mol% Ca doped HZO film, contributing to the optimum ferroelectric property with the largest remnant polarization of 14.00 μC/cm² after 10⁵ cycles. Additionally, the leakage current density is observed to decrease with increasing Ca content, which is mainly associated with the changes of grain size and surface roughness. As a result, the endurance is significantly improved in the Ca doped films, and an excellent endurance of 10¹⁰ cycles is achieved in the 2.5 mol% Ca doped film. These results suggest that Ca doping can enhance the ferroelectric and endurance properties of HZO films by optimizing the phase and morphological structure.