Ferroelectric-field-effect-enhanced electroresistance in metal/ferroelectric/semiconductor tunnel junctions

Abstract

Ferroelectric tunnel junctions (FTJs), composed of two metal electrodes separated by an ultrathin ferroelectric barrier, have attracted much attention as promising candidates for non-volatile resistive memories. Theoretical and experimental works have revealed that the tunnelling resistance switching in FTJs originates mainly from a ferroelectric modulation on the barrier height. However, in these devices, modulation on the barrier width is very limited, although the tunnelling transmittance depends on it exponentially as well. Here we propose a novel tunnelling heterostructure by replacing one of the metal electrodes in a normal FTJ with a heavily doped semiconductor. In these metal/ferroelectric/semiconductor FTJs, not only the height but also the width of the barrier can be electrically modulated as a result of a ferroelectric field effect, leading to a greatly enhanced tunnelling electroresistance. This idea is implemented in Pt/BaTiO3/Nb:SrTiO3 heterostructures, in which an ON/OFF conductance ratio above 10(4), about one to two orders greater than those reported in normal FTJs, can be achieved at room temperature. The giant tunnelling electroresistance, reliable switching reproducibility and long data retention observed in these metal/ferroelectric/semiconductor FTJs suggest their great potential in non-destructive readout non-volatile memories.

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.…”

Overcoming the Fundamental Barrier Thickness Limits of Ferroelectric Tunnel Junctions through BaTiO3/SrTiO3 Composite Barriers

“…12,13 Up to recently, most studies of FTJs have focused on improving device performance by modifying the electrode materials. [14][15][16][17][18][19][20] Typical examples include the use of lightly doped semiconductors, [14][15][16] For a thick barrier, these obstacles can be avoided, but the tunneling current becomes too small for realizing a practically useful device. As an alternative, several groups have theoretically proposed a new kind of FTJ using an FE/paraelectric (FE/PE) composite barrier.…”

Side‐Gated In2O3 Nanowire Ferroelectric FETs for High‐Performance Nonvolatile Memory Applications

“…Poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) copolymer is one of the typical organic ferroelectric polymers that is frequently employed in various nanoelectronic devices because of its room temperature ferroelectricity, large remnant polarization, and easy forming process with the required annealing temperature below 140 °C 11, 12, 13, 14. Importantly, the stable remnant polarization of the P(VDF‐TrFE) dielectric layer can enable an ultrahigh local electrostatic field in the semiconductor channel, which is much larger than that produced by the gate bias in traditional field‐effect transistors;15, 16 in this case, the transport properties of the channel can be effectively modulated under a relatively low gate bias or even stayed in depletion or accumulation state after the gate bias is removed. However, since P(VDF‐TrFE) is highly soluble in common organic solvents, it is cumbersome to fabricate electronic devices with P(VDF‐TrFE) in the top‐gated configuration with short channel lengths (i.e., sub‐μm) via conventional ultraviolet or electron‐beam lithography (EBL) techniques 5, 17.…”

“…Moreover, in view of the performance variation accompanied with the nonuniformity of In 2 O 3 NW thickness as well as process deviation in the device fabrication, a statistical study of electrical properties of fabricated devices is necessary in order to obtain a better understanding and to confirm the geometrical effect here. The turn‐off voltage ( V off , defined as the gate voltage at which I ds reaches its minimum when V gs sweeps from +50 to −50 V in this study) is chosen to reveal the polarization switching induced by the P(VDF‐TrFE) film because the turn‐on voltage ( V on , defined as the gate voltage at which I ds starts to increase when V gs sweeps from −50 to +50 V) is always less stable as compared with V off and the switching from the on‐state to the off‐state is relatively sharp (see Figure S5 in the Supporting Information) 15, 32, 33. Particularly, we compile a statistics regarding the value of E off , where E off refers to the turn‐off electric field and it can be simply calculated by V off / D .…”