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HfO2-based ferroelectrics show tremendous potential for applications in computing technologies, but questions remain as to what dictates the stabilization of the desired phase. Here, it is demonstrated that the substrate the film is grown on is more influential than factors such as thickness, defect content, and strain. The presence of different possible polymorphs of Hf0.5Zr0.5O2 are observed to vary widely for different substrate materials—with La0.67Sr0.33MnO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and Al2O3 being (more) optimal for stabilizing the ferroelectric-orthorhombic phase. This substrate effect is found to be more influential than any changes observed from varying the film thickness (7.5–60 nm), deposition environment (oxygen vs argon), and annealing temperature (400–600 °C) in vacuum (10−5 Torr). X-ray diffraction and scanning transmission electron microscopy verify the phases present, and capacitor-based studies reveal ferroelectric behavior (or lack thereof) consistent with the phases observed. First-principles calculations suggest that forming oxygen vacancies in Hf0.5Zr0.5O2 lowers its work function, driving electrons away and helping to stabilize the ferroelectric phase. Substrates with a high work function (e.g., La0.67Sr0.33MnO3) facilitate this electron transfer but must also have sufficient ion conductivity to support oxygen-vacancy formation in Hf0.5Zr0.5O2. Together, these observations help clarify key factors essential to the stabilization of HfO2-based ferroelectrics. 

There is an increasing desire to utilize complex functional electronic materials such as ferroelectrics in next-generation microelectronics. As new materials are considered or introduced in this capacity, an understanding of how we can process these materials into those devices must be developed. Here, the effect of different fabrication processes on the ferroelectric and related properties of prototypical metal oxide (SrRuO3)/ferroelectric (BaTiO3)/metal oxide (SrRuO3) heterostructures is explored. Two different types of etching processes are studied, namely, wet etching of the top SrRuO3 using a NaIO4 solution and dry etching using an Ar+-ion beam (i.e., ion milling). Polarization-electric-field hysteresis loops for capacitors produced using both methods are compared. For the ion-milling process, it is found that the Ar+ beam can introduce defects into the SrRuO3/BaTiO3/SrRuO3 devices and that the milling depth strongly influences the defect level and can induce a voltage imprint on the function. Realizing that such processing approaches may be necessary, work is performed to ameliorate the imprint of the hysteresis loops via ex situ “healing” of the process-induced defects by annealing the ferroelectric material in a barium-and-oxygen-rich environment via a chemical-vapor-deposition-style process. This work provides a pathway for the nanoscale fabrication of these candidate materials for next-generation memory and logic applications. 

In ferroelectric heterostructures, the interaction between intrinsic polarization and the electric field generates a rich set of localized electrical properties. The local electric field is determined by several connected factors, including the charge distribution of individual unit cells, the interfacial electromechanical boundary conditions, and chemical composition of the interfaces. However, especially in ferroelectric perovskites, a complete description of the local electric field across micro-, nano-, and atomic-length scales is missing. Here, by applying four-dimensional scanning transmission electron microscopy (4D STEM) with multiple probe sizes matching the size of structural features, we directly image the electric field of polarization vortices in (PbTiO3)16/(SrTiO3)16 superlattices and reveal different electric field configurations corresponding to the atomic scale electronic ordering and the nanoscale boundary conditions. The separability of two different fields probed by 4D STEM offers the possibility to reveal how each contributes to the electronic properties of the film. 

Abstract The pursuit of smaller, energy‐efficient devices drives the exploration of electromechanically active thin films (<1 µm) to enable micro‐ and nano‐electromechanical systems. While the electromechanical response of such films is limited by substrate‐induced mechanical clamping, large electromechanical responses in antiferroelectric and multilayer thin‐film heterostructures have garnered interest. Here, multilayer thin‐film heterostructures based on antiferroelectric PbHfO₃and ferroelectric PbHf_1‐xTi_xO₃overcome substrate clamping to produce electromechanical strains >4.5%. By varying the chemistry of the PbHf_1‐xTi_xO₃layer (x = 0.3‐0.6) it is possible to alter the threshold field for the antiferroelectric‐to‐ferroelectric phase transition, reducing the field required to induce the onset of large electromechanical response. Furthermore, varying the interface density (from 0.008 to 3.1 nm⁻¹) enhances the electrical‐breakdown field by >450%. Attaining the electromechanical strains does not necessitate creating a new material with unprecedented piezoelectric coefficients, but developing heterostructures capable of withstanding large fields, thus addressing traditional limitations of thin‐film piezoelectrics. 

Abstract The dielectric gap between the scanning probe microscopy (SPM) tip and the surface of a ferroelectric using conductive atomic force microscopy and piezoresponse force microscopy (PFM) is investigated. While the gap functions as a dielectric layer, it also allows tunneling current to inject charges into the ferroelectric when a critical loading force between 10–20 µN is applied to a tip with a radius of 25 nm under a bias voltage of 0.5 V. It is observed that the permittivity of the dielectric gap determines the coercive voltage measured by the piezoresponse hysteresis loop. While such studies done in air often produce coercive voltages much larger than those studied for the same materials in capacitor‐based studies, the use of high permittivity media such as water (ɛ_r= 79) or silicone oil (ɛ_r= 2.1‐2.8) produces coercive fields that more closely match those measured in conventional capacitor‐based polarization hysteresis loop measurements. Furthermore, using water as a dielectric medium in PFM imaging enhances the accuracy in extracting the amplitude and phase data from periodically poled lithium niobate crystals. These findings provide insight into the nanoscale phenomena of polarization switching instigated by the SPM tip and provide a pathway to improved quantitative studies. 

Abstract Highly responsive, voltage‐tunable dielectrics are essential for microwave‐telecommunication electronics. Ferroelectric/relaxor materials have been leading candidates for such functionality and have exhibited agile dielectric responses. Here, it is demonstrated that relaxor materials developed from antiferroelectrics can achieve both ultrahigh dielectric response and tunability. The system, based on alloying the archetypal antiferroelectric PbZrO₃with the dielectric BaZrO₃, exhibits a more complex phase evolution than that in traditional relaxors and is characterized by an unconventional multi‐phase competition between antiferroelectric, ferroelectric, and paraelectric order. This interplay of phases can greatly enhance the local heterogeneities and results in relaxor characteristics while preserving considerable polarizability. Upon studying Pb_1‐xBa_xZrO₃forx= 0‐0.45, Pb_0.65Ba_0.35ZrO₃is found to provide for exceptional dielectric tunability under low bias fields (≈81% at 200 kV cm⁻¹and ≈91% at 500 kV cm⁻¹) at 10 kHz, outcompeting most traditional relaxor ferroelectric films. This high tunability is sustained in the radio‐frequency range, resulting in a high commutation quality factor (>2000 at 1 GHz). This work highlights the phase evolution from antiferroelectrics (with lower, “positive” dielectric tunability) to relaxors (with higher, “negative” tunability), underscoring a promising approach to develop relaxors with enhanced functional capabilities and new possibilities. 

There is growing interest in the study of thin-film pyroelectric materials because of their potential for high performance thermal-energy conversion, thermal sensing, and beyond. Electrothermal susceptibilities, such as pyroelectricity, are known to be enhanced in proximity to polar instabilities, and this is conventionally accomplished by positioning the material close to a temperature-driven ferroelectric-to-paraelectric phase transition. The high Curie temperature (TC) for many ferroelectrics, however, limits the utility of these materials at room-temperature. Here, the nature of pyroelectric response in thin films of the widely studied multiferroic Bi1−xLaxFeO3 (x = 0–0.45) is probed. While BiFeO3 itself has a high TC, lanthanum substitution results in a chemically induced lowering of the ferroelectric-to-paraelectric and structural-phase transition. The effect of isovalent lanthanum substitution on the structural, dielectric, ferroelectric, and pyroelectric response is investigated using reciprocal-space-mapping studies; field-, frequency-, and temperature-dependent electrical measurements; and phase-sensitive pyroelectric measurements, respectively. While BiFeO3 itself has a rather small pyroelectric coefficient at room temperature (∼−40 µC/m2 K), 15% lanthanum substitution results in an enhancement of the pyroelectric coefficient by 100% which is found to arise from a systematic lowering of TC. 

Abstract The development of next‐generation in‐memory and neuromorphic computing can be realized with memory transistors based on 2D ferroelectric semiconductors. Among these, In₂Se₃is the interesting since it possesses ferroelectricity in 2D quintuple layers. Synthesis of large amounts of In₂Se₃crystals with the desired phase, however, has not been previously achieved. Here, the gram‐scale synthesis of α‐In₂Se₃crystals using a flash‐within‐flash Joule heating method is demonstrated. This approach allows the synthesis of single‐phase α‐In₂Se₃crystals regardless of the conductance of precursors in the inner tube and enables the synthesis of gram‐scale quantities of α‐In₂Se₃crystals. Then, α‐In₂Se₃flakes are fabricated and used as a 2D ferroelectric semiconductor FET artificial synaptic device platform. By modulating the degree of polarization in α‐In₂Se₃flakes according to the gate electrical pulses, these devices exhibit distinct essential synaptic behaviors. Their synaptic performance shows excellent and robust reliability under repeated electrical pulses. Finally, it is demonstrated that the synaptic devices achieve an estimated learning accuracy of up to ≈87% for Modified National Institute of Standards and Technology patterns in a single‐layer neural network system.