Electrical Properties of Epitaxial Ferroelectric Heterostructures

Abstract

In the context of miniaturization of devices, ferroelectric materials are used as multifunctional materials for their well-known intrinsic properties, especially for the switching of polarization in an applied electric field. The high-quality epitaxial thin film structures are used for the possibility to study different effects as low dimensions, interface, strain and strain gradients on ferroelectric materials and other electric characteristics, also representing a possibility to obtain new phenomena and properties that can be used for development of new devices with different functionalities. This chapter is a summary of the ferroelectric and dielectric behaviour of epitaxial thin films of Pb(Zr,Ti)O 3 (PZT) and BaTiO 3 (BTO) obtained by pulsed laser deposition and the correlation with structural quality of the layers and with different electrostatic conditions induced either by electrodes or by the different interlayers. For this purpose in the first part, studies regarding the influence of the substrates and of different top electrodes are performed for Pb(Zr,Ti) O 3 (PZT) 52/48. In the second part, we focused on artificial multiferroic structures from alternating layers of PZT 20/80 or BaTiO 3 (BTO) as ferroelectric phase and CoFe 2 O 4 (CFO) as magnetic material. We found that interface configuration and strain engineering could control ferroelectric hysteresis, the capacitance or the leakage current magnitude.

Negative Capacitance for Stabilizing the Logic State in a Tunnel Field-Effect Transistor

“…The internal electric field may be generated due to the gradient in the strain distribution in the flake or a nonhomogeneous spatial distribution of defects like Cu + vacancies. 42 All of the presented evidence unambiguously confirms the existence of FE−PE heterophases in the 2D CIPS−IPS, positioning it as a promising nonvolatile element in vdW heterostructures. The material is then tested for its applications in a prototype FEFET.…”

“…An imprint voltage of around 2 V is observed in the hysteresis loop of the C – V curve, indicating the presence of an internal electric field between the electrodes. The internal electric field may be generated due to the gradient in the strain distribution in the flake or a nonhomogeneous spatial distribution of defects like Cu + vacancies …”

Ten States of Nonvolatile Memory through Engineering Ferromagnetic Remanent Magnetization

“…Recent research efforts toward multilevel nonvolatile devices include the phase change memory, resistive random access memory and ferroelectric transistor, where multiple resistance states are respectively demonstrated by utilizing phase change, resistance switching and multiferroic exchange coupling. In spite of intense research efforts and significant success, it is still very challenging to increase the number of levels with high fidelity more than four states.…”

“…In spite of intense research efforts and significant success, it is still very challenging to increase the number of levels with high fidelity more than four states. Moreover, it even seems impossible to achieve a common approach toward multiple resistance states in different systems, considering the fact that the dominated physical mechanisms vary from system to system . To overcome this issue, we propose a general remanent magnetism engineering method for realizing multiple reliable magnetic and resistance states, not depending on a specific material or device structure.…”