Schottky barrier height and modulation due to interface structure and defects in Pt|MgO|Pt heterojunctions with implications for resistive switching (original) (raw)
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Random and localized resistive switching observation in Pt/NiO/Pt
Physica Status Solidi-rapid Research Letters, 2007
Resistive memory switching devices based on transition metal oxides are now emerging as a candidate for nonvolatile memories. To visualize nano-sized (10 nm to 30 nm in diameter) conducting filamentary paths in the surface of NiO thin films during repetitive switching, current sensing–atomic force microscopy and ultra-thin (<5 nm) Pt films as top electrodes were used. Some areas (or spots), which were assumed to be the beginning of the conducting filaments, appeared (formation) and disappeared (rupture) in a localized and random fashion during the switching and are thought to contribute to resistive memory switching. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Field-induced resistive switching in metal-oxide interfaces
Applied Physics Letters, 2004
We investigate the polarity-dependent field-induced resistive switching phenomenon driven by electric pulses in perovskite oxides. Our data show that the switching is a common occurrence restricted to an interfacial layer between a deposited metal electrode and the oxide. We determine through impedance spectroscopy that the interfacial layer is no thicker than 10 nm and that the switch is accompanied by a small capacitance increase associated with charge accumulation. Based on interfacial I − V characterization and measurement of the temperature dependence of the resistance, we propose that a field-created crystalline defect mechanism, which is controllable for devices, drives the switch.
Resistive switching transition induced by a voltage pulse in a Pt/NiO/Pt structure
Applied Physics Letters, 2010
We have observed a switching transition between bistable memory switching and monostable threshold switching in Pt/NiO/Pt structure. Bistable memory switching could be changed to monostable threshold switching by applying a positive electrical pulse with height of 2 V and width between 10 −2 and 10 −4 s. The change is reversible by applying a negative electrical pulse with the same height and width. By considering polarity-and width-dependence of the switching transition and compositional difference on electrical properties in NiO x , we have proposed a model in which the migration of oxygen ions ͑O 2− ͒ is responsible for the switching transition in Pt/NiO/Pt structures.
In this study, we investigated the resistive switching (RS) behavior of Pt/Nb-doped SrTiO 3 (Pt/Nb:STO) single-crystal junctions in air and vacuum. We performed steady-state electrical characterizations: the direct current (DC) current-voltage relationship and relaxation current-time dependence under an applied voltage step. The ideality factor of the junction suggested the existence of interface states and tunneling current. We observed that the relaxation current followed the Curie-von Schweidler law; electrical conduction was dominated by a space-charge-limited current based on charge recombination at the interface states. The dynamic electric response was obtained using an alternating current (AC) conductance technique. The carrier lifetime at the interface traps was largely dependent on the resistance state and the ambient environment. Thus, surface potential modification by charge capture/release at the interface traps played a crucial role in the RS of our junctions. Additionally, the ambient effect showed that oxygen desorption (adsorption) at the Nb:STO surface increased (decreased) the interface state density. Finally, an RS model based on interface states in Pt/Nb:STO was proposed.
Resistive switching in metal–ferroelectric–metal junctions
Applied Physics Letters, 2003
The aim of this work is to investigate the electron transport through metal-ferroelectric-metal ͑MFM͒ junctions with ultrathin barriers in order to determine its dependence on the polarization state of the barrier. To that end, heteroepitaxial Pt/Pb(Zr 0.52 Ti 0.48 )O 3 /SrRuO 3 junctions have been fabricated on lattice-matched SrTiO 3 substrates. The current-voltage (I -V) characteristics of the MFM junctions involving a few-nanometer-thick Pb(Zr 0.52 Ti 0.48 )O 3 barriers have been recorded at temperatures between 4.2 K and 300 K. Typical I -V curves exhibit reproducible switching events at well-defined electric fields. The mechanism of charge transport through ultrathin barriers and the origin of the observed resistive switching effect are discussed.
Modeling for bipolar resistive memory switching in transition-metal oxides
Physical Review B, 2010
A model which describes the bipolar resistive switching in transition-metal oxides is presented. To simulate the effect of switching, we modeled results of doping by oxygen vacancies along with variable Schottky barrier and resistor. The model simultaneously predicts three key features of experimental measurements: the rectifying behavior in high resistance states, abrupt switching, and the existence of bistable resistance states. Our model is based on modulation of Schottky barrier formed by variable resistance oxide layer at the metal-oxide interface. Experimental measurements of the Pt/ Ta 2 O 5 / TaO x / Pt structure matched very well with our nonvolatile resistive switching model.
Mechanism for bipolar resistive switching in transition-metal oxides
Physical Review B, 2010
We introduce a model that accounts for the bipolar resistive switching phenomenom observed in transition metal oxides. It qualitatively describes the electric field-enhanced migration of oxygen vacancies at the nano-scale. The numerical study of the model predicts that strong electric fields develop in the highly resistive dielectric-electrode interfaces, leading to a spatially inhomogeneous oxygen vacancies distribution and a concomitant resistive switching effect. The theoretical results qualitatively reproduce non-trivial resistance hysteresis experiments that we also report, providing key validation to our model.
Nanoscale Resistive Switching in Ultrathin PbZr 0.2 Ti 0.8 O 3 –La 0.7 Sr 0.3 MnO 3 Bilayer
physica status solidi (b), 2020
Electron tunneling through a ferroelectric barrier has received increasing interest in recent years because the polarization in the barrier was found to control the tunneling current. [1-11] Early work on tunneling through a ferroelectric started with theoretical considerations. [1] Multiferroic four-state tunnel junctions have been introduced by combining the ferroelectric barrier with spin-polarized tunneling in magnetic tunnel junctions. [5,7,11] Both BaTiO 3 and PbZr x Ti 1Àx O 3 (PZT, x ¼ 0-0.5) have been used as ferroelectric for the tunnel barrier. [8-11] For proper function as a tunnel barrier, ferroelectric layers of about 1-5 nm thickness need to be reversibly switched. This poses the challenge of applying very large electric fields to the barrier, because the coercive fields of ferroelectric films grow strongly with reduced thickness. [12] Often, the required electric field is of the order of 1-10 MV cm À1. An electric field of this magnitude can drive processes which are of electrochemical nature and change the chemical composition in or near the tunnel barrier. Such phenomena are part of another very active research area: resistive switching based on voltage-driven ionic movements has been vastly explored for memory applications in the last 15 years. [13] Until now, ferroelectric PbZr x Ti 1Àx O 3 (PZT, x ¼ 0-0.5) has very rarely been studied with respect to resistive switching based on ionic motions. Choi et al. measured electrical transport and switching of PZT (x ¼ 0.3) capacitors with a Pt (top) and a La 0.5 Sr 0.5 CoO 3 (bottom) electrode, varying the thickness of the PZT layer between 17 and 160 nm. [14] They found bipolar resistive switching instead of a polarization reversal for a PZT thickness of ≤34 nm. The characteristics of bipolar resistive switching can be described as follows: during cycling the voltage applied to the Pt electrode from zero to positive maximum, negative maximum, and back to zero, the resistance drops at a positive threshold voltage indicating a transition to a so-called low-resistance state (LRS). The LRS turns back to the high-resistance state (HRS) at a negative threshold voltage. The current versus voltage (I-V) loop thus roughly follows the shape of the number eight, starting with a counterclockwise loop at positive voltages. (Our measurements presented here are unipolar; nevertheless, Figure 1b can be used for an impression of how the positive half of the bipolar I-V loop would look like.) The work of Choi et al. showed that thin PZT layers display similar bipolar resistive switching such as SrTiO 3 which has often been studied and utilized in resistive switching elements. [15-17] Qin et al. studied tunnel barriers made of PZT and BaTiO 3 as well as dielectric SrTiO 3 in nominally symmetric electrode configurations with LSMO on both sides and find bipolar resistive switching without polarization reversal. [18] All three titanates show similar behavior despite their different electric nature. Notably, the application of a positive threshold voltage