A comprehensive study of bipolar operation in resistive switching memory devices

Abstract

The authors present a new numerical analysis method to investigate the conduction filament dynamics of a resistive switching nonvolatile metal-insulator-metal structured memory device. This comprehensive method, utilizing the Gibbs free energy criteria as a leading indicator and allowing simulation of all resistive memory operational phases (forming, set and reset), is presented for the first time. The formation and rupture of an oxygen vacancies based conduction filament are simulated to demonstrate a cycle of operation in a hafnium oxide based resistive forming layer. Starting from a random initial distribution of defect states, on to a formed conduction filament and ending in a ruptured state. Detailed plots of the physical parameters within the resistive layer are provided to gain deeper understanding of the conduction filament kinetics and introduce the concept of "hot spots", referring to random localized initial agglomeration of oxygen vacancies in which temperature surges is favored and contribute to initiate the conductive filament formation. By basing the method on well known thermodynamic properties and the Metropolis algorithm, simulation reliability and efficiency are obtained. The presented results confirm previously published data demonstrating the switching characteristics of hafnium based resistive random access memory.

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“…Resistive states in the device are interchangeable as shown by the I – V sweeps in Figure C. The figure highlights the stress‐induced formation and annihilation of traps indicated by step‐like transitions . A positive sweep (gray) over a slightly conductive LRS induced more trap formation and increased the conductivity even further, as verified by the successive black curve.…”

“…The figure highlights the stressinduced formation and annihilation of traps indicated by step-like transitions. [38,39] A positive sweep (gray) over a slightly conductive LRS induced more trap formation and increased the conductivity even further, as verified by the successive black curve. The I-V curves show a relatively symmetric behavior after the transition to an LRS as it effectively results in the formation of a conductive filament.…”

“…What possible mechanisms could account for the observed photoinduced response? The experimental results suggest that the main cause is a combination of surface plasmon‐induced electron–photon excitations and trap‐assisted hopping conduction . The schematic band diagrams shown in Figure G‐I illustrate these mechanisms at work.…”

“…When combined with rising temperatures within the dielectric, this stress drives both the creation and annihilation of traps. Reversing the bias polarity repels the negatively charged oxygen ions back toward the positively charged traps, where they may recombine, and the device is reset back to an HRS . This state is shown by the band diagram of Figure H and represents the off‐bipolar state (LRS‐OFF).…”

“…Figure G shows I – V sweeps exhibiting these conductance changes that resulted from the successive application of 500 ms voltage pulses with different polarities and amplitudes to the TE. The amplitudes in this case were chosen to be relatively high to generate enough electric stress to facilitate trap generation–recombination events . Directions of change are marked by colored arrows and corresponding labels indicating the bias and number of pulses.…”