Ferroelectric/Multiferroic Tunnel Junctions for Multifunctional Applications

Abstract

Ferroelectric and multiferroic tunnel junctions (FTJ/MFTJs) are a novel class of next generation nonvolatile memories devices that display simultaneous magnetic spin, electric dipole ordering, and tunneling with cross coupling and have drawn increasing interest due to their multifunctionality for a variety of device applications. With the rapid development of thin‐film growth techniques and characterization tools in the last decade, it is possible to do extensive research in the area of polar barrier tunnel junctions (TJ). This chapter summarizes how the ferroelectric (FE) (polar) nature of the barrier changes the tunneling probability, and briefly, we expose several aspects to be considered in the synthesis of FTJ and MFTJ, such as critical thickness for ferroelectricity, effect of the depolarization field, and the role of interface on ferroelectricity at the nanoscale level. In addition, we include recent research results in FTJ/MFTJ. We focus in particular on PZT (lead zirconate titanate) and BTO (barium titanate) in case of ferroelectric tunnel junction (FTJ), and BFO (bismuth ferrite) and BMO (bismuth manganite) single‐phase multiferroics (MFs) used as barriers in multiferroic tunnel junctions (MFTJ). The variety of interesting physical phenomena of these TJ and their multifunctional properties for various technological applications make the research in this field challenging and promising.

Multifunctional magnetoelectric materials for device applications

“…The experimental and theoretical findings suggest that FE persists in ultrathin films (~3 nm) [217], which opens up the possibility of further miniaturising devices based on FE materials. A way to exploit the FE properties of ultrathin films and the multifunctional character of MF materials is to design tunnel junctions (TJ) integrating FE or MF films as the tunnel barrier or making the TJ itself a multiferroic heterostructure [218]. At present, TJ using an insulating (nonpolar) barrier is the basis of MRAMs [219].…”