Operando Surface Probe Microscopy Reveals Electrochemical Origins of Reliability Variability in Hafnia Ferroelectrics

Abstract

Device-to-device and sample-to-sample variability remains a major obstacle to the reliable implementation of hafnia-based ferroelectrics, even in nominally identical structures fabricated under similar processing conditions. This highlights the need for operando diagnostic probes that provide process-relevant feedback beyond conventional structural phase analysis. Here, we demonstrate that operando nanoscale surface measurements serve as sensitive probe of the local electrochemical processes governing reliability in hafnia ferroelectric devices. Using epitaxial rhombohedral Y:HfO2 films grown on La0.67Sr0.33MnO3 (LSMO)-buffered SrTiO3 as a model system, we combine operando atomic force microscopy, conductive AFM, piezoresponse force microscopy, and correlative STEM-EELS to directly link surface evolution with interfacial electrochemistry. Devices exhibiting wake-up show a spatially uniform increase in surface height, arising from homogeneous oxidation of the LSMO electrode followed by oxygen migration into the ferroelectric layer during polarization switching. In contrast, leaky devices display pronounced surface roughening and blister formation, originating from spatially inhomogeneous oxidation states in the pristine LSMO electrode that promote competing oxygen evolution reactions at the LSMO/Y:HfO2 interface. The accompanying electron generation produces leakage which is transient. Guided by these mechanistic insights, we introduce simple modifications to the processing conditions, without altering the optimized ferroelectric phase, that suppress the competing electrochemical pathways and reproducibly yield 100% ferroelectric devices. More broadly, this work establishes operando surface evolution as a powerful nanoscale diagnostic of hidden electrochemical processes and provides a practical route for improving the reliability and reproducibility of hafnia-based ferroelectric devices.