Electronic band alignment and electron transport in Cr/BaTiO3/Pt ferroelectric tunnel junctions

Abstract

Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO3(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO3/Pt junctions with a sub-μm Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ∼30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO3/Pt (Cr/BaTiO3) interface +0.42(−0.03) eV following downward to upward polarization reversal.

Ferroelectric tunnel junctions for information storage and processing

“…They successively determined the interfacial BaTiO 3 /Pt and Cr/BaTiO 3 barrier heights, and used these parameters to fit I versus V DC measured on Cr/BaTiO 3 /Pt tunnel junctions in the ON and OFF states at room temperature. Hence, the OFF/ON ratio of 30 at room temperature in these FTJs can be interpreted by a modulation of the potential profile of the tunnel barrier in the direct tunnelling regime 41 .…”

“…There are, however, too many unknown physical parameters (dielectric constant, polarization, effective screening lengths, effective mass of tunnelling electrons and so on) to reasonably fit experimental data. To overcome this limitation, Zenkevich et al 41 performed hard X-ray photoemission experiments to gather more information on the electrode/ferroelectric interfacial electronic properties. They successively determined the interfacial BaTiO 3 /Pt and Cr/BaTiO 3 barrier heights, and used these parameters to fit I versus V DC measured on Cr/BaTiO 3 /Pt tunnel junctions in the ON and OFF states at room temperature.…”

“…However, some influence of electrochemical phenomena correlated with ferroelectric polarization switching cannot be completely excluded 40 . Alongside with ab initio calculations 42,55 , investigations of the actual metal/ferroelectric interfaces with spectroscopic techniques, such as X-ray photoemission spectroscopy 41 and advanced transmission electron microscopy-based techniques 88,89 , will bring further insights on the understanding of TER.…”

Giant electrode effect on tunnelling electroresistance in ferroelectric tunnel junctions

“…Nevertheless, high-quality epitaxial films grown on suitable substrates were found to possess necessary ferroelectric properties even at nanoscale thicknesses [14][15][16][17][18] , which may be attributed to the enhancement of the out-of-plane polarization by substrate-induced lattice strains 19 and the elastic stabilization of a single-domain state 20 . Based on these advancements, various FTJs have recently been successfully fabricated and the TER effect was revealed experimentally and confirmed theoretically [21][22][23][24][25][26][27][28][29][30][31] . Moreover, the functioning of solid-state memories based on FTJs has been demonstrated 3,32 and the memristive behaviour with resistance variations exceeding two orders of magnitude was observed for FTJs with the BaTiO 3 (BTO) barrier 32,33 .…”

“…The choice of electrode materials, due to different screening and chemical properties at the interface, seems to have pronounced influence on the TER effect [21][22][23][24][25][26][27][28][29][30][31][32][33] . Therefore, it is essential to examine the impact of different electrode materials on the TER characteristics of FTJs.…”