Chapter 6 - Interface engineering of ferroelectric thin-film heterostructures

Abstract

In a polycrystalline ferroelectric (FE) film, the disordered arrangement of grains and the existence of mesoscale defects, such as grain boundaries, will complicate the interface environment of the film, making tailoring of the interface state uncontrollable. On the other hand, theoretical and experimental studies have shown that the hetero-interface of an epitaxial FE film grown on a single crystalline substrate is regular and well ordered. The bottom electrode, acting as both a conductive layer and a growth template, plays a key role in the epitaxial growth of the FE film. The crystalline structure and orientation, microscopic defect density, interface barrier height, depletion layer characteristics, and other structural properties of the film are directly determined by this electrode layer and its associated bottom interface, that is, the interface upon which the film is grown (growth interface). These effects will be discussed following a general introduction on the engineering of the bottom interface of a FE film. Another type of bottom interface/“growth interface” exists in FE multilayers, which can be either periodic (in superlattices) or finite (in FE bilayers). These interfaces usually generate coupling effects between neighboring FE–FE layers or FE–dielectric layers. This kind of interface effects will be discussed separately.