Search for: All records

Abstract 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. 

Abstract Rare‐earth disilicates are a focus of study for use as environmental barrier coatings in gas‐turbine engines. These coatings require thermomechanical and thermochemical stability at elevated temperatures and properties can be tailored through the use of multicomponent rare‐earth disilicates. Producing rare‐earth disilicates via sol–gel is documented in literature, but there are differing procedures with varying phase purities. This work establishes trends that dictate the effects of water content, pH, and heat treatment conditions that determine the final phase purity of Yb, Er, Lu, Sc, and Y disilicate powders made via sol–gel. The phase(s) of the powders were identified and quantified using X‐ray diffraction (XRD) to extract weight fractions. In situ XRD during heating from room temperature to 1200°C was used to observe the crystallization and phase evolution of the sol–gel‐based powders, allowing for the identification of a rarely reported low temperature triclinic phase in ytterbium‐, erbium‐, and lutetium‐based disilicate sol–gels that forms prior to transformation into a monoclinic phase. Ex situ XRD allowed for the phase identification of sol–gels processed at 1400°C. These experiments demonstrated that phase‐pure disilicates could be formed under conditions with no intentional water additions, a target pH of 2, and long heat treatment times at high temperatures (e.g., 1400°C). These conditions remain valid for not only single‐cation rare‐earth disilicates of Yb, Er, Lu, Sc, and Y but also a multicomponent disilicate containing equimolar concentrations of all of these cations. 

Abstract The presence of the top electrode on hafnium oxide‐based thin films during processing has been shown to drive an increase in the amount of metastable ferroelectric orthorhombic phase and polarization performance. This “Clamping Effect,” also referred to as the Capping or Confinement Effect, is attributed to the mechanical stress and confinement from the top electrode layer. However, other contributions to orthorhombic phase stabilization have been experimentally reported, which may also be affected by the presence of a top electrode. In this study, it is shown that the presence of the top electrode during thermal processing results in larger tensile biaxial stress magnitudes and concomitant increases in ferroelectric phase fraction and polarization response, whereas film chemistry, microstructure, and crystallization temperature are not affected. Through etching experiments and measurement of stress evolution for each processing step, it is shown that the top electrode locally inhibits out‐of‐plane expansion in the HZO during crystallization, which prevents equilibrium monoclinic phase formation and stabilizes the orthorhombic phase. This study provides a mechanistic understanding of the clamping effect and orthorhombic phase formation in ferroelectric hafnium oxide‐based thin films, which informs the future design of these materials to maximize ferroelectric phase purity and corresponding polarization behavior.