Origin of the Ultra‐nonlinear Switching Kinetics in Oxide‐Based Resistive Switches

Abstract

for the VCM effect. [ 15 , 18 , 19 ] The VCM effect may take place at dislocations that act as conducting fi laments, [ 18 ] or homogenously over a somewhat larger interface region, [ 20 ] or both within the same sample. [ 21 ] To fulfi ll the requirements of a suitable nonvolatile memory, a cell should be scalable down to a few nanometers. As a further important requirement a WRITE voltage of a few volts must be suffi cient to switch a cell within less than 100 ns and a READ voltage of a few tenths of a volt should leave the resistance state unchanged for ten years. This requirement corresponds to a nonlinear voltage acceleration of the kinetics of many orders of magnitude, also known as the voltage-time dilemma. The origin of this strong voltage acceleration has been attributed to electric-fi eld-enhanced ion-hopping mobility, although possible contributions of temperature-activated ion mobility have also been mentioned. [22][23][24][25][26][27][28] Another explanation for this effect in the literature is the electric-fi eld-enhanced recombination/generation of oxygen vacancies. [ 29 , 30 ] Herein, we report experimental results of the switching kinetics of interface-type VCM cells based on epitaxial SrTiO 3 thin fi lms as a model system, which reveal a highly nonlinear voltage-time dependency. Based on a 2D axisymmetric fi nite element simulation model, which allows a quantitative discrimination of fi eld and temperature contributions, we are able to identify the temperature acceleration as the origin of this nonlinearity. Using this model we discuss the scaling properties of the VCM cell concept and prove its feasibility on the nanoscale. Electrical CharacterizationThin-fi lm devices consisting of a SrTiO 3 (STO) thin fi lm grown epitaxially on a conducting Nb-doped SrTiO 3 (STO:Nb) and a Ti top electrode were characterized by performing quasistatic current-voltage ( I-V ) studies as well as by defi ned voltagepulse measurements. The voltage was always applied to the top electrode of the devices. The quasistatic I-V sweep was also employed to execute the initial electroforming process and to achieve a defi ned OFF state prior to the pulse studies. An overview of the setup and the measurement procedure is shown in Figure 1 . Before and after a SET voltage pulse was applied to a memory cell, its resistance was measured quasistatically to determine the resistance change. The quasistatic I-V sweep Origin of the Ultra-nonlinear Switching Kinetics in Oxide-Based Resistive SwitchesExperimental pulse length-pulse voltage studies of SrTiO 3 memristive cells are reported, which reveal nonlinearities in the switching kinetics of more than nine orders of magnitude. The results are interpreted using an electrothermal 2D fi nite element model. The nonlinearity arises from a temperature increase in a few-nanometer-thick disc-shaped region at the Ti electrode and a corresponding exponential increase in oxygen-vacancy mobility. The model fully reproduces the experimental data and it provides essential design rules for opti...

Single ferroelectric-domain photovoltaic switch based on lateral BiFeO3 cells

“…22 According to the Nernst-Einstein relation, we note that the diffusivity of V O 2 þ can vary by many orders of magnitude for the typical activation energy of B1.0 eV of various perovskite oxides. 23,24 In Figures 5a and c, we show that the single-domain switching and the related photovoltaic characteristics remained qualitatively unchanged, regardless of the E-field poling temperatures. We only observed a small increase in I ph at 300 K. In the multidomain channel, however, domain reversal became notably inhomogeneous at 77 K, as shown in Figure 5b, leading to the absence of photovoltaic characteristics, as shown in Figure 5d.…”

Anomalous effect due to oxygen vacancy accumulation below the electrode in bipolar resistance switching Pt/Nb:SrTiO3 cells

“…5 For the BRS phenomenon in oxides, the same principle is used commonly to explain the relationship between the density variation of V o¨a nd the electronic resistance. 1-4 Using the V o¨m odel, researchers have explained many intriguing BRS phenomena successfully, 6,7 including the resistance state retention time, the switching speed, and the capability to withstand degradation. However, the V o¨m odel also leaves many questions unanswered, because the real spatial distribution of V o¨i nside BRS oxides has rarely been investigated at the nanoscale.…”

“…In many BRS oxides, the current flow is localized to nanoscale conducting channels, so it is difficult to determine exactly where the resistance switching occurs. [2][3][4][7][8][9] In most cases, the quantity of V o¨i n typical a S. Lee oxide thin films is quite low to be detected using direct imaging techniques, such as transmission electron microscopy (TEM). 10 In this study, we used Nb-doped SrTiO 3 (Nb:SrTiO 3 ) cells with Pt electrodes, which show BRS phenomena.…”

“…18 For this study, we also took into account of the Joule heating effects, which is known to accelerate the hopping speed of V o¨. 7 The details of the Joule heating calculation are explained in the simulation methods section of the supplementary material. 18 With the known V o¨d istribution, we calculated the position-dependent conduction band, E C (x), or the Schottky barrier from the solution of Poisson's equation: 5 …”

A memristor random circuit breaker model accounting for stimulus thermal accumulation

“…Salaoru et al [13] applied pulse stimulus on TiO2-based RRAM devices to study the coexistence behaviour of memristor and memcapacitor. Stephan et al [14] explored the ultra nonlinear switching behaviour between the resistive state change and the applied pulse width/amplitude. Meanwhile, there arises numerous new RRAM features from the pulsing characterization process such as non-linear current-voltage relation [15], multi-states storage capacities [10,15], statistical behaviours of the programming threshold voltage [15], voltage-time dilemma during the resistive state tuning [2,13].…”