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Register a new userResistive switching in reverse: voltage driven formation of a transverse insulating barrier
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Application of an electric stimulus to a material with a metal-insulator transition can trigger a large resistance change. Resistive switching from an insulating into a metallic phase, which typically occurs by the formation of conducting filaments parallel to the current flow, has been an active research topic. Here we present the discovery of an opposite, metal-to-insulator switching that proceeds via nucleation and growth of an insulating barrier perpendicular to the driving current. The barrier formation leads to an unusual N-type negative differential resistance in the current-voltage characteristics. Electrically inducing a transverse barrier enables a novel approach to voltage-controlled magnetism. By triggering a metal-to-insulator resistive switching in a magnetic material, local on/off control of ferromagnetism can be achieved by a global voltage bias applied to the whole device.
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The discovery of new mechanisms of controlling magnetic properties by electric fields or currents furthers the fundamental understanding of magnetism and has important implications for practical use. Here, we present a novel approach of utilizing resistive switching to control magnetic anisotropy. We study a ferromagnetic oxide that exhibits an electrically triggered metal-to-insulator phase transition producing a volatile resistive switching. This switching occurs in a characteristic spatial pattern: the formation of a transverse insulating barrier inside a metallic matrix resulting in an unusual ferromagnetic/paramagnetic/ferromagnetic configuration. We found that the formation of this voltage-driven paramagnetic insulating barrier is accompanied by the emergence of a strong uniaxial magnetic anisotropy that overpowers the intrinsic material anisotropy. Our results demonstrate that resistive switching is an effective tool for manipulating magnetic properties. Because resistive switching can be induced in a very broad range of materials, our findings could enable a new class of voltage-controlled magnetism systems.
The resistive switching phenomenon in MgO-based tunnel junctions is attributed to the effect of charged defects inside the barrier. The presence of electron traps in the MgO barrier, that can be filled and emptied, locally modifies the conductance of the barrier and leads to the resistive switching effects. A double-well model for trapped electrons in MgO is introduced to theoretically describe this phenomenon. Including the statistical distribution of potential barrier heights for these traps leads to a power-law dependence of the resistance as a function of time, under a constant bias voltage. This model also predicts a power-law relation of the hysteresis as a function of the voltage sweep frequency. Experimental transport results strongly support this model and in particular confirm the expected power laws dependencies of resistance. They moreover indicate that the exponent of these power laws varies with temperature as theoretically predicted.
Two promising strategies for achieving efficient control of magnetization in future magnetic memory and non-volatile spin logic devices are spin transfer torque from spin polarized currents and voltage-controlled magnetic anisotropy (VCMA). Spin transfer torque is in widespread development as the write mechanism for next-generation magnetic memory, while VCMA offers the potential of even better energy performance due to smaller Ohmic losses. Here we introduce a 3-terminal magnetic tunnel junction (MTJ) device that combines both of these mechanisms to achieve new functionality: gate-voltage-modulated spin torque switching. This gating makes possible both more energy-efficient switching and also improved architectures for memory and logic applications, including a simple approach for making magnetic memories with a maximum-density cross-point geometry that does not require a control transistor for every MTJ.
The development prospects of memristive elements for non-volatile memory with use of the metal-dielectric-metal sandwich structures with a thin oxide layer are due to the possibility of reliable forming the sustained functional states with quantized resistance. In the paper we study the properties of fabricated memristors based on the non-stoichiometric $ZrO_2$ nanotubes in different resistive switching modes. Anodic oxidation of the $Zr$ foil has been used to synthesize a zirconia layer of $1.7$ $mu$$m$ thickness, consisting of an ordered array of vertically oriented nanotubes with outer diameter of 75 nm. $Zr/ZrO_2/Au$ sandwich structures have been fabricated by mask magnetron deposition. The effects of resistive switching in the $Zr/ZrO_2/Au$ memristors in unipolar and bipolar modes have been investigated. The resistance ratios $geq3cdot10^4$ between high-resistance (HRS) and low-resistance (LRS) states have been evaluated. It has been founded the conductivity of LRS is quantized in a wide range with minimum value of $0.5G_0=38.74$ $mu$$S$ due to the formation of quantum conductors based on oxygen vacancies ($V_O$). Resistive switching mechanisms of $Zr/ZrO_2/Au$ memristors with allowing for migration of $V_O$ in an applied electric field have been proposed. It has been shown that the ohmic type and space charge limited conductivities are realized in the LRS and HRS, correspondingly. We present the results which can be used for development of effective memristors based on functional $Zr/ZrO_2/Au$ nanolayered structure with multiple resistive states and high resistance ratio.
We report on resistive switching of memristive electrochemical metallization devices using 3D kinetic Monte Carlo simulations describing the transport of ions through a solid state electrolyte of an Ag/TiO$_{text{x}}$/Pt thin layer system. The ion transport model is consistently coupled with solvers for the electric field and thermal diffusion. We show that the model is able to describe not only the formation of conducting filaments but also its dissolution. Furthermore, we calculate realistic current-voltage characteristics and resistive switching kinetics. Finally, we discuss in detail the influence of both the electric field and the local heat on the switching processes of the device.
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