Mechanically controlled nonlinear dielectrics

Structural characteristics of heteroepitaxy. (A) Diagram of BSTO and BTO systems. (B) Scheme of epitaxial relationships. (C) Unscheduled X-ray scan of a 2θ-θ heterostructure. AU, arbitrary units. (D) Rocking curves of SRO (222), BTO (111) and AZO (002). (E) Φ-scanning of muscovite {202}, SRO {002}, BTO {002} and AZO {101}. (F) TEM cross-sectional image at the interface and corresponding fast Fourier transform (FFT) patterns in the insets. Courtesy of Science Advances, doi: 10.1126 / sciadv.aaz3180.

Stress-sensitive barium-strontium titanate (BaX-sr1 x-TiO3Perovskite systems are widely used due to their excellent non-linear dielectric behavior. In the new report on Scientific achievements, D.L. Co. and a research group in materials science and engineering, physics, electronics and computer science in Taiwan, Hong Kong and the USA have developed new heterostructures, including paraelectric0.5Sr0.5TiO3 (BSTO) and ferroelectric BaTiO3 (BTO) epitaxial on flexible muscovite substrate. The use of mechanical force through simple bending is adjustable dielectric constant (potential of electric energy) for BSTO in the range from -77 to 36%, as well as channel current based on BTO ferroelectric field effect transistors, two orders of magnitude. Co. et al. studied a detailed mechanism, studying the phase transition and determining the band structure to implement the phase field simulation and provide theoretical support. The field opens a new avenue for mechanically controlled components based on high quality oxide heteroepitaxy,

The periodic configuration of atoms in a solid is the result of energy minimization, when the participating atoms and their corresponding arrangement can determine material propertiesAs a result, material scientists can dynamically adjust the frequency of atomic arrangement or the application of deformations in the fundamental approach to adjusting the functionality of the material. Researchers have previously proposed several approaches for imposing a load on materials, including the application of hydrostatic pressure observe the shift of the diffraction peaks using X-ray diffraction analysis as direct evidence of a change in the lattice under the influence of an external force. For example, external stimuli, such as magnetic fields, electric fields, and light lighting, can undergo a lattice change due to magnetostriction, electrostriction, and photostriction, The concept of applying mechanical force to materials can be realized through manual bending, as this is the easiest way to cause deformation of the material. To apply deformation without absorption by defect formation, material scientists require high-quality materials, such as single crystals or epitaxial films, although most single crystals cannot be mechanically bent.

Mechanically controlled nonlinear dielectrics

Different results of two-dimensional muscovite bending. In this study, glue was used to seal the edges of the heterostructures, providing a strong bond of the heterostructure. This is the key to applying voltage to the heterostructure. Courtesy of Science Advances, doi: 10.1126 / sciadv.aaz3180.

Two-dimensional (2-D) layered oxide Muscovites are suitable candidates due to their excellent mechanical flexibility and high melting point (~ 12600C to 12900FROM). If deformation can be applied to a nonlinear dielectric grating, then it can change its ability to accumulate charge and the magnitude of the ferroelectric polarization. Nonlinear dielectric materials provide a strong connection between the structure and properties of the lattice among traditional nonlinear dielectrics.non-toxic perovskite BaXSr1 xTiO3 Systems have shown high sensitivity to the use of deformation. As a result, Ko et al. selected paraelectric Ba0.5Sr0.5TiO3 (BSTO) and ferroelectric BaTiO3 In this study, mechanical bending control is demonstrated as model systems.

Research team set up ferroelectric to paraelectric phase transition BaXSr1 xTiO3 a system for monitoring the corresponding dielectric and ferroelectric properties by mechanical bending. They used capacitive voltage (CV), polarization voltage (PV), and volt-ampere (IV) measurements to characterize dielectric constant BSTO and ferroelectric properties of BTO. They also built a BTO-based ferroelectric field effect transistor (FeFET) with a highly mobile semiconductor layer of aluminum alloyed zinc (AZO) and measured its channel current to study the effect of bending on the BSTO and BTO FeFET capacitor. The team observed a change in the lattice during bending using Raman spectroscopy and used X-ray photoelectron spectroscopy to highlight the effect of BTO polarization on the electronic structure in the AZO semiconductor layer under various bending conditions.

Mechanically controlled nonlinear dielectrics

Ferroelectric properties. (A) Relationship between the curvature and thickness of the muscovite substrate. (B) The dielectric constant of BSTO for various bending curves. (C) Tunability of an alternating electric field at various bends of a bend. (D) C-V shape of a butterfly in a bent state and dielectric constant in various bending states. (E) Hysteresis loops of polarization stress at various bends under tension and compression. Photo: Dan Li Ko, Department of Materials Science and Engineering, Chao Tong National University, Hsinchu 30010, Taiwan. (F) BSTO and BTO transition temperature for various bending curves. (G) The amplitude of the Raman signal with curved and curved curvatures of 0.1, 0.13, 0.2 and 0.285 mm -1. (H) Raman spectra of a heterostructure at temperatures ranging from room temperature to 170 ° C. Courtesy Science Advances, doi: 10.1126 / sciadv.aaz3180.

Co. et al. designed the BSTO capacitor and BTO FeFET systems on muscovite substrates with excellent crystallinity, which the researchers investigated using X-ray diffraction. They noted the high crystalline quality of the heterostructure without secondary phases and calculated the quality of the crystals of each layer using rocking curve measurement. To study the microstructure of the material, they characterized a heterostructure with high resolution transmission electron microscopy and studied deformation by mechanical bending using muscovite substrates due to their mechanical flexibility, where thinner Muscovites showed better bending during the experiments.

The team applied stress through mechanical bending to observe changes in BTO ferroelectricity and BSTO dielectric constant. They measured capacitive voltage (CV) and polarization voltage (PV) to see if the polarization intensity of BTO is gradually attenuated by mechanical bending. The electrical tunability of the BSTO capacitor reached approximately 60-70%, which indicates the high quality of the heterostructures, and the dielectric constant could be regulated only by the electric field, while increasing or decreasing during positive (tensile strain) and negative (compressive strain) bending. curvature. Co. et al. tuned the amount of charge accumulated in this dielectric material, stretching the lattice architecture, and noted that the behavior associated with non-linear dielectric properties can be controlled and repeated in mechanical bending with great potential in practice.

Mechanically controlled nonlinear dielectrics

Characteristics of flexible FeFET. (A) Schematic diagram of a flexible FeFET. (B) Different results of bending the ID-VG curve counterclockwise with VG ranging from -1 to 6 V. (C) ID-VG curve counterclockwise with bending compression. (D) The ratio of bending to bending in the current state. (E) Five rounds of durability testing began after 1000 bending cycles, and the on / off current ratio was two orders of magnitude. (F) The IDS of the AZO / BSTO transistor shows a slight change in bending. Courtesy of Science Advances, doi: 10.1126 / sciadv.aaz3180.

The team then investigated the ability of mechanical bending to change ferroelectric properties using several measurements, including temperature-dependent Raman spectroscopy, to study the phase transition of ferroelectric materials. The results provided direct evidence of controlling the ferroelectric state by mechanical bending, and further optimization of the device design allowed them to convert a simple and tunable ferroelectric capacitor into a mechanically controlled transistor. Bending compression and tension reduced the current in the open state, but the effect of deformation was obvious when bending under tension. Scientists have confirmed that the substrate AZO / BTO / SRO (strontium ruthenate) / muscovite is a transistor with mechanical control. The team confirmed these effects using piezoreflective force microscopy (PFM) and Kelvin probe force microscopy (KPFM).

Mechanically controlled nonlinear dielectrics

Scanning probe microscopy in bending with a bend of 0.285 mm -1. (A) the PFM phase is off-plane after the polishing process. (B) The surface potential of KPFM was detected immediately after the measurement of PFM. The band structure of FeFET was investigated using XPS measurement. (C) Zn 2p and Ba 3d XPS spectra of the AZO / BTO sample in the Pdown and Pup states. (D) Zn 2p and Ba 3d XPS spectra of the AZO / BTO sample in a state of bending, bending, and flattening. (E and F) Schematic diagrams illustrating the alignment of energy zones at the AZO / BTO heterojunction in a bending and bending state. Courtesy of Science Advances, doi: 10.1126 / sciadv.aaz3180.

Thus, D.L. Co and colleagues developed a flexible oxide heteroepitaxial capacitor and FeFET using paraelectric BSTOs, ferroelectric BTOs, and AZO semiconductor layers on a two-dimensional muscovite substrate. The BSTO capacitor showed high tunability of its dielectric constant under mechanical bending. In the FeFET component, they achieved a change of two orders of magnitude in the ratio of the on / off current relative to the BTO ferroelectricity. The results of the study provided them with critical information about a mechanism in which flexible and customizable electrical properties were possible due to simple mechanical bending. This breakthrough will provide a promising path for future applications of mechanically tuned technologies.

Controlled functional ferroelectric domain walls under a piezoelectric microscope

Additional Information:
Ying Hao Chu. Van der Waals oxide heteroepitaxy, npj quantum materials (2017). DOI: 10.1038 / s41535-017-0069-9

D. L. Co et al. Mechanically controlled nonlinear dielectrics, Scientific achievements (2020). DOI: 10.1126 / sciadv.aaz3180

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Mechanically Operated Nonlinear Dielectrics (2020, March 16)
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