Modulating light absorption and multiferroic properties of BiFeO3-based ferroelectric films by the introduction of ZnO layer

Pure bismuth ferrite (BiFeO3, BFO) and ZnO thin films, as well as BFO/ZnO and ZnO/BFO composite thin films were successfully deposited by a sol-gel process on Pt/Ti/SiO2/Si and FTO/glass substrates, respectively. The chemical composition, surface morphology, optical properties, and multiferroicity were systematically investigated. X-ray diffraction and electron microscopy measurements were used to determine the crystalline phase and to analyze the surface morphology. Evidently, the absorption edges of both BFO/ZnO and ZnO/BFO films show a redshift, broadening the absorption range. The leakage current density decreases with the introduction of ZnO, and the ferroelectricity was significantly improved of the bilayers. Thereinto, BFO/ZnO and ZnO/BFO show the highest saturate polarization (2P s) of 46.7 μc/cm2 and the maximum remanent polarization (2P r) of 18.5 μc/cm2, respectively. Meanwhile, the magnetization measurement revealed that both BFO/ZnO and ZnO/BFO exhibiting an enhanced magnetization, especially, BFO/ZnO displays the highest saturation magnetization (2M s, 68.87 emu/cm3) and remanent magnetization (2M r, 4.87 emu/cm3).

A Brief Review on the Ferroelectric Fluorite-Structured Nanolaminate

Ferroelectricity can be induced in fluorite-structured oxides such as HfO2 and ZrO2, a feature of increasing interest in both academia and industry. Initially, most research focused on solid solution films, but recently, it has been suggested that nanolaminates with independent HfO2 and ZrO2 layers may show electrical and physical properties superior to those of solid solution samples. It was reported that the nanolaminate samples could have remanent polarization higher than that of solid solution film or a wider composition window for robust ferroelectricity compared to the solid solution films. In this review, the existing literature on fluorite-structured nanolaminates is comprehensively reviewed.

Electric field-induced crystallization of ferroelectric hafnium zirconium oxide

Ferroelectricity in crystalline hafnium oxide thin films is strongly investigated for the application in non-volatile memories, sensors and other applications. Especially for back-end-of-line (BEoL) integration the decrease of crystallization temperature is of major importance. However, an alternative method for inducing ferroelectricity in amorphous or semi-crystalline hafnium zirconium oxide films is presented here, using the newly discovered effect of electric field-induced crystallization in hafnium oxide films. When applying this method, an outstanding remanent polarization value of 2P$$_{\mathrm{R}}$$ R = 47 $$\upmu$$ μ C/cm$$^{2}$$ 2 is achieved for a 5 nm thin film. Besides the influence of Zr content on the film crystallinity, the reliability of films crystallized with this effect is explored, highlighting the controlled crystallization, excellent endurance and long-term retention.

Magnetoelectric and Multiferroic Properties of BaTiO3/NiFe2O4/BaTiO3 Heterostructured Thin Films Grown by Pulsed Laser Deposition Technique

Development of lead-free BaTiO3/NiFe2O4/BaTiO3 (BTO/NFO/BTO) trilayer structure thin films is significant for the realization of eco-friendly and implantable microelectromechanical systems (MEMS)-based devices. In the present work, we report BTO/NFO/BTO trilayer structure as a representative ferroelectric/ferromagnetic/ferroelectric (FE/FM/FE) system deposited on Pt(111)/TiO2/SiO2/Si using Pulsed Laser Deposition (PLD) technique. We report the ferroelectric, magnetic, and ME properties of BTO/NFO/BTO trilayer nanoscale heterostructure having dimensions 140/80/140 nm, at room temperature. High room temperature dielectric constant ~2145 at 100 Hz with low dielectric loss ~0.05 at 1 MHz is observed. Further, the deposited (BTO/NFO/BTO) tri-layered thin films showed magnetoelectric, multiferroic behavior with remanent polarization of 8.63 μCcm−2 at about 0.25 MV/cm and a reasonably high saturation magnetization of ~16 emu/cm3 at ~10 kOe is witnessed at room temperature. Tri-layered films have shown interesting magnetoelectric (ME) coupling coefficient (αE) ~54.5 mV/cm Oe at room temperature.

Polarization Reversal Characteristics in Capacitors with a Metal/Insulator/Ferroelectric/Metal Structure

A metal/insulator/ferroelectric/metal structure was fabricated using a covering of approximately 10 nm thick of an insulating polystyrene film on a ferroelectric poly(vinylidene fluoride-trifluoroethylene) film. To fabricate several samples, the thickness of the ferroelectric film was held constant while the thickness of the insulating film was varied from 8 to 24 nm. The polarization– voltage relationships were measured to extract the main parameters, in this case the remanent polarization, depolarization, coercive voltage and biased voltage values. As the insulating film becomes thicker, the remanent polarization and coercive voltage values tended to increase. On the other hand, depolarization and biased voltage values decreased. By analyzing the above mentioned parameters, a certain optimum insulator thickness could be predicted. This work shows that metal/insulator/ferroelectric/metal devices are more useful than metal/ferroelectric/metal capacitors.

Robust ferroelectricity enhancement of PZT thin films by a homogeneous seed layer

With its excellent ferroelectric properties such as large dielectric constant and large remanent polarization, PZT thin films are extensively used in micro-sensors and other devices. In this study, the sol-gel process was used to fabricate Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1−x)O3 seed islands. The experimental consequences demonstrate that all the Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1−x)O3 seeds show pure perovskite phase with no other impurity phases, and the electrical properties of Pb(Zr0.52Ti0.48)O3 thin films modified by Pb(ZrxTi1−x)O3 seed islands with different Zr/Ti ratios are improved, such as remanent polarization increased, dielectric properties increased, coercive electric field decreased, leakage current density decreased, etc. In particular, the electrical properties of the Pb(Zr0.52Ti0.48)O3 thin films with Pb(ZrxTi1−x)O3 seed islands are the most optimal when the x is 0.52. This paper provides a new technique for optimizing the electrical properties of PZT thin films, which is of great significance for breaking through the bottleneck of the development of ferroelectric memory.