Environmental Control of Ferroelectricity in Hafnia Films

Ferroelectricity in hafnia films has triggered significant research interest over the past decade due to its immense promise for next-generation memory devices. However, the origin of ferroic behavior at the nanoscale and the means to control it remain an open question, with the consensus being that it deviates from conventional ferroelectrics. In this work, a novel approach is presented to tune ferroelectric properties of hafnia through environmental control using piezoresponse force microscopy (PFM). A reversible transition from non-ferroelectric to ferroelectric behavior by modulating the surrounding atmosphere is demonstrated. Notably, the domain relaxation dynamics exhibit striking sensitivity to environmental factors, including ambient conditions, specific gas compositions (N₂, CO₂, O₂), and humidity levels. The critical role of surface water removal, gas molecule adsorption, and their interactions with near-surface oxygen vacancies is identified and the injected charge in determining ferroelectricity in uncapped hafnia films. These insights reveal a significant strategy for stabilizing ferroic responses by carefully regulating the chemical environment, offering new possibilities for precise control in hafnia-based films.