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The development of magnetic random access memory requires very reliable magnetic tunnel junctions (MTJs). However these devices are prone to dielectric breakdown. To investigate the reliability of the MTJs, we performed constant voltage stress tests. This study shows the area scaling and the voltage dependence of the time-to-breakdown t[sub BD] of exchange biased, naturally oxidized MTJs. The fraction of broken devices F is plotted on a Weibull scale. The Weibull fit of our data shows clearly that t[sub BD] scales with the area, meaning that the breakdown sites are randomly distributed. Moreover, the Weibull distributions have a constant slope β (=0.35) and show no tails. This suggests that only one breakdown mode is observed. It is not clear yet whether an intrinsic or extrinsic failure mechanism is causing the breakdown, but considering the small Weibull slope, extrinsic breakdown caused by randomly distributed process-induced defects in the oxide is most plausible. Second, the voltage dependence of t[sub BD] is studied. To fit the data, a linear dependence of 1og(t[sub BD]) on stress voltage is assumed. It is however not yet proven whether this model is applicable for ultrathin Al[sub 2]O[sub 3] barriers. [ABSTRACT FROM AUTHOR]

Uniform switching in RRAM devices has been modeled as field driven transition of multiple defects in the dielectric switching layer. In this analytic model, conductance through the stack is calculated using a resistive network. The effect of neighboring defects in the computation of the effective electric field is accounted for by constructing the potential function and taking its gradient. The model captures the gradual switching and the on- and off- state correlation during cycling. Furthermore, scaling the devices limits the number of active defects resulting in local effects due to favorably positioned critical defects. Abrupt drifts in the memory window can be understood as a consequence of movement of these critical defects. All simulations have been corroborated by a TiN/a-Si/TiO 2 /TiN based stack. [ABSTRACT FROM AUTHOR]

In this letter, a tip-induced cell relying on the conductive atomic force microscope is proposed. It is verified as a referable replica of an integrated resistive random access memory (RRAM) device. On the basis of this cell, the functionality of sub-10 nm resistive switching is confirmed in hafnium oxide stack. Moreover, the low current switching behavior in the sub-10 nm dimension is found to be more pronounced than that of a 50×50 nm2 device. It shows better ON/OFF ratio and low leakage current. The enhanced memory performance is ascribed to a change in the shape of the conductive filament as the device dimensions are reduced to sub-10 nm. Therefore, device downscaling provides a promising approach for the resistance optimization that benefits the RRAM array design. [ABSTRACT FROM AUTHOR]

In this paper, we develop a Quantum-Point-Contact (QPC) model describing the state conduction in a W/Al2O3/TiW/Cu Conductive-Bridging Memory cell (CBRAM). The model allows describing both the voltage- and the temperature-dependence of the conduction. For deep current levels, a resistance component is added in series to the point-contact constriction to account for electron scattering in the residual filament. The fitting of single-particle perturbation also allowed to estimate the number and effective size of the conduction-controlling particles in the QPC constriction. The results clearly point to smaller particles for CBRAM (Cu particles) as compared to oxide-based resistive RAM involving oxygen-vacancy defects, which is discussed as a possible origin of deeper reset level obtained in CBRAM. We also evidence a beneficial impact of this smaller particle size on lower Random-Telegraph-Noise amplitude measured on CBRAM devices. [ABSTRACT FROM AUTHOR]

Transition metal oxide-based resistor random access memory (RRAM) takes advantage of oxygen-related defects in its principle of operation. Since the change in resistivity of the material is controlled by the oxygen deficiency level, it is of major importance to quantify the kinetics of the oxygen diffusion, key factor for oxide stoichiometry. Ab initio accelerated molecular dynamics techniques are employed to investigate the oxygen diffusivity in amorphous hafnia (HfOx, x = 1.97, 1.0, 0.5). The computed kinetics is in agreement with experimental measurements. [ABSTRACT FROM AUTHOR]

In this letter, we compare the switching performances of Cu-based CBRAM cells having either Al2O3 or SiO2 dielectric layer. Both electrical and physical characterizations revealed different Cu mobility in the two dielectrics, impacting forming/switching speed and variability as well as functionality at low current. The modeling of the conduction also indicated different filament shapes in the two dielectrics. Based on the results, dielectrics allowing high Cu mobility are required when filament temperature is low, i.e., for low-current application ( <10~\mu \textA ), while dielectrics allowing moderate Cu mobility are more appropriate for higher current ranges ( \ge 10~\mu \textA ), whereby Cu mobility is highly assisted by temperature. [ABSTRACT FROM AUTHOR]

Impact of set/reset pulse duration and amplitude on the endurance failure modes of TiN\Ta2O5\Ta cells is investigated and is related to interaction between Oxygen and TiN bottom electrode during reset. Hourglass electrical switching simulation of conductive filament temperature during reset transient and ab-initio calculation of reaction energy further support this degradation mechanism. Based on this understanding, endurance improvement is achieved by using shorter reset pulse and/or using inert Ru bottom electrode. [ABSTRACT FROM AUTHOR]