8 Search Results

In this paper we examine the influence of controllable polarization reversal and built-in electric fields on pyroelectric and electrocaloric effects in a BaTiO₃ thin film using a modified indirect method. We find that the magnitude of the sample's change in polarization with temperature is sensitive to the degree of polarization reversal. The pyroelectric response is small at low fractions of switched polarization and grows larger by several factors as larger fractions of polarization are reversed. This polarization reversal-sensitive pyroelectric behavior is the result of an internal built-in field, which has the effect of destabilizing low fractions of switched polarization andmore » producing diminished pyroelectric effect. Greater fractions of switched polarization are more stable against backswitching and permit a larger pyroelectric response. Our findings highlight a characterization method for polarization-dependent pyroelectric effects in ferroelectric thin films, where built-in field effects are also present.« less

In this paper, we report a cryogenic-temperature study on the evolution of the ferroelectric properties of epitaxial Hf_0.5Zr_0.5O₂ thin films on silicon. Wake-up, endurance, and fatigue of these films are found to be intricately correlated, strongly hysteretic, and dependent on available thermal energy. Field-dependent measurements reveal a decrease in polarization with temperature, which has been determined not to be an intrinsic change of the material property, rather a demonstration of the increase in the coercive bias of the material. Our findings suggest that a deficiency in thermal energy suppresses the mobility of defects presumed to be oxygen vacancies during wake-upmore » and trapped injected charge during fatigue, which is responsible for polarization evolution during cycling. This permits accelerated wake-up and fatigue effects at high temperatures where thermal energy is abundant but delays these effects at cryogenic temperatures.« less

Epitaxial ferroelectric HfO2 films are the most suitable to investigate intrinsic properties of the material and for prototyping emerging devices. Ferroelectric Hf_0.5Zr_0.5O₂(111) films were epitaxially stabilized on La_2/3Sr_1/3MnO₃(001) electrodes. This epitaxy, considering the symmetry dissimilarity and the huge lattice mismatch, is not compatible with conventional mechanisms of epitaxy. In this work, to gain insight into the epitaxy mechanism, scanning transmission electron microscopy characterization of the interface was performed, revealing arrays of dislocations with short periodicities. Additionally, these observed periodicities agree with those expected for domain matching epitaxy, indicating that this unconventional mechanism could be the prevailing factor in the stabilizationmore » of ferroelectric Hf0.5Zr0.5O2 with (111) orientation in the epitaxial Hf_0.5Zr_0.5O₂(111)/La_2/3Sr_1/3MnO₃(001)heterostructure.« less

Rotational polar textures in nominally tetragonal BaTiO ₃ were experimentally observed by STEM in BaTiO ₃ /SrTiO ₃ superlattices of appropriate periodicity ( n ).

Tunnel devices based on ferroelectric Hf_0.5Zr_0.5O₂ (HZO) barriers hold great promises for emerging data storage and computing technologies. The resistance state of the device can be changed through use of a suitable writing voltage. However, the microscopic mechanisms leading to the resistance change are an intricate interplay between ferroelectric polarization controlled barrier properties and defect-related transport mechanisms. Herein, the fundamental role of the microstructure of HZO films determining the balance between those contributions is demonstrated. The HZO film presents coherent or incoherent grain boundaries, associated to the coexistance of monoclinic and orthorhombic phases, which are dictated by the mismatch withmore » the substrates for epitaxial growth. These grain boundaries are the toggle that allows to obtain either large (up to ≈450%) and fully reversible genuine polarization controlled electroresistance when only the orthorhombic phase is present or an irreversible and extremely large (≈10³–10⁵%) electroresistance when both phases coexist.« less

Conventional strain engineering of epitaxial ferroelectric oxide thin films is based on the selection of substrates with a suitable lattice parameter. In this work, we show that the variation of oxygen pressure during pulsed laser deposition is a flexible strain engineering method for epitaxial ferroelectric BaTiO₃ films either on perovskite substrates or on Si(001) wafers. This unconventional growth strategy permits continuous tuning of strain up to high levels (ε > 0.8%) in films greater than one hundred nanometers thick, as well as selecting the polar axis orientation to be either parallel or perpendicular to the substrate surface plane.

The integration of epitaxial BaTiO₃ films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO₃/LaNiO₃/SrTiO₃ heterostructure is grown monolithically on Si(001). The BaTiO₃ films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm². Lastly, this result paves the way towards the fabrication of lead-free BaTiO₃ ferroelectric memories on silicon platforms.