Giant electrode effect on tunnelling electroresistance in ferroelectric tunnel junctions

Abstract

Among recently discovered ferroelectricity-related phenomena, the tunnelling electroresistance (TER) effect in ferroelectric tunnel junctions (FTJs) has been attracting rapidly increasing attention owing to the emerging possibilities of non-volatile memory, logic and neuromorphic computing applications of these quantum nanostructures. Despite recent advances in experimental and theoretical studies of FTJs, many questions concerning their electrical behaviour still remain open. In particular, the role of ferroelectric/electrode interfaces and the separation of the ferroelectric-driven TER effect from electrochemical ('redox'-based) resistance-switching effects have to be clarified. Here we report the results of a comprehensive study of epitaxial junctions comprising BaTiO 3 barrier, La 0.7 Sr 0.3 MnO 3 bottom electrode and Au or Cu top electrodes. Our results demonstrate a giant electrode effect on the TER of these asymmetric FTJs. The revealed phenomena are attributed to the microscopic interfacial effect of ferroelectric origin, which is supported by the observation of redox-based resistance switching at much higher voltages.

Ferroelectric control of spin-transfer torque in multiferroic tunnel junctions

“…The TER associated with ferroelectric polarization switching has been observed experimentally in BaTiO 3 -and PbTiO 3 -based FTJs in which either La 2/3 Sr 1/3 MnO 3 or SrRuO 3 is used as one of the electrodes while the other side of the ferroelectric thin film is in contact with the tip of an atomic force microscope [24][25][26] . The predicted simultaneous TMR and TER effects 23 have also been demonstrated experimentally in La 2/3 Sr 1/3 MnO 3 /BaTiO 3 /Fe (or Co) MFTJs [27][28][29][30][31][32][33][34] . Although the majority of the work deals with low bias, the existence of TER at finite bias has been predicted based on calculations using a semiclassical approximation 19 and first-principles 35 in FTJs, and model tight-binding calculations in MFTJs 36 .…”

Ferroelectricity and Self-Polarization in Ultrathin Relaxor Ferroelectric Films

“…Recently, there are many reports on self-polarization of ultrathin normal ferroelectric films (with thicknesses below 10 nm) just after deposition as revealed by PFM30313233343536, in addition to some thicker ferroelectric films (with thicknesses above 100 nm)37383940. Several mechanisms have been proposed, such as the Schottky contact related built-in electric field at the ferroelectric/electrode interface333441, surface ionic adsorption36, different terminated interface37, flexoelectric effects39, etc.…”

Resonant tunneling across a ferroelectric domain wall

“…The structural and/or electronic asymmetry of the FTJ plays a decisive role for the TER effect. It can be achieved using dissimilar electrodes [9,[19][20][21][22], through interface engineering [13,[23][24][25][26], or applied bias [27,28]. Additionally, using ferromagnetic electrodes in a FTJ adds functionality, forming a multiferroic tunnel junction (MFTJ) [29].…”