Electrode-Dependent Phase Stabilization and Polarization Response in Hafnium Zirconium Oxide Thin Films

Hafnium oxide-based ferroelectrics have emerged as a leading candidate for next-generation nonvolatile memory devices, yet the relationships between fabrication conditions and ferroelectric response remain poorly understood. The structural complexity of hafnium oxide and the constraints associated with nanoscale dimension and multilayer device geometry make conventional characterization methods unsuitable for resolving detailed microstructure characteristics. Here, we use four-dimensional scanning transmission electron microscopy to perform phase and orientation mapping and quantitatively examine the impact of electrode materials on the microstructure and remnant polarization of ferroelectric hafnium-zirconium oxide capacitors. We show that the observed remnant polarization is correlated with the polar phase fraction and alignment of the polar axis with respect to the growth direction. We also demonstrate that the interfacial oxide layer and the nonpolar polymorphs of hafnium oxide play a critical role in determining the ferroelectric polarization, as these structures give rise to depolarization fields.