Electrodes: the real performers in single-barrier ferroelectric tunnel junctions

To study the role of the emitter and collector electrode materials in Ferroelectric Tunnel Junctions (FTJs), an in-depth theoretical investigation of 4 single-barrier FTJs (Pt/BTO/SRO, Pt/BTO/Pt, SRO/BTO/SRO, and SRO/BTO/Pt) is reported. Compared with all known conduction mechanisms in FTJ, it is found that direct quantum tunneling provides the most predominant contribution to the current density in the above systems for the bias range of 0-1.2 V. The lowering of the barrier height and asymmetry in the barrier profile which determines the tunneling current is controlled by the potential drop in the accumulation region in the emitter and the depletion region in the collector which depends on the ratio of screening length, delta, to permittivity, epsilon, of the corresponding electrodes. The tunneling electro-resistance ratio (TER) is found to have significant values for bias potential V > vertical bar P vertical bar(delta(1)epsilon/(1) + delta(2)/epsilon(2)) wherein the screening charge density sigma(s), and the net charge density in the barrier layer (sigma(s) - P) remain negative resulting in the pull-down of the barrier toward the Fermi level and producing a negative slope in the barrier to increase the tunneling current. Among the studied systems, Pt/BTO/SRO provides the highest TER. Specifically, Pt/24 angstrom BTO/SRO system with an active device length of 5.6 nm is found to have a current density of 2.54 x 10(4)A/cm(2) and 1.28 x 10(2)A/cm(2) in the ON and OFF state and a TER of nearly 20,000% at the bias of 0.71 V confirming to the necessary conditions of efficient application in memory devices.