A simulation study has been performed to analyze resistive switching (RS) phenomena in valence change memories (VCM) based on a HfO2 dielectric. The kernel of the simulation tool consists of a 3D kinetic Monte Carlo (kMC) algorithm implemented self-consistently with the 3D Poisson and heat equations. These VCM devices show filamentary conduction, their RS operation is based on the destruction and regeneration of an ohmic conductive filament (CF) composed of oxygen vacancies. The physics underlying the RS operation is described by means of processes linked to generation of oxygen vacancies, oxygen ion migration and recombination between vacancies and oxygen ions that can be accurately described by using the electric field and temperature distributions in the dielectric. The studied devices consist of TiN/Ti/HfO2/W stacks where the Ti capping layer plays the role of oxygen ion getter material. The simulation tool is useful for obtaining information of internal physical variables, explaining RS dynamics and the CFs evolution from the microscopic viewpoint in terms of their size and shape under different electrical input signals; particularly, the pulsed operation regime has been studied in depth. Furthermore, interesting phenomena, such as partial SETs within overall RESET processes can be accurately reproduced.

A physical model for trap-assisted inelastic tunnel current through potential barriers in semiconductor structures has been developed. The model is based on the theory of multiphonon transitions between detrapped and trapped states and the only fitting parameters are those of the traps ͑energy level and concentration͒ and the Huang-Rhys factor. Therefore, dependences of the trapping and detrapping processes on the bias, position, and temperature can be obtained with this model. The results of the model are compared with experimental data of stress induced leakage current in metal-oxide-semiconductor devices. The average energy loss has been obtained and an interpretation is given of the curves of average energy loss versus oxide voltage. This allows us to identify the entrance of the assisted tunnel current in the Fowler-Nordheim regime. In addition, the dependence of the tunnel current and average energy loss on the model parameters has been studied.

An in-depth study of reset processes in RRAMs (Resistive Random Access Memories) based on Ni/HfO2/Si-n+ structures has been performed. To do so, we have developed a physically based simulator where both ohmic and tunneling based conduction regimes are considered along with the thermal description of the devices. The devices under study have been successfully fabricated and measured. The experimental data are correctly reproduced with the simulator for devices with a single conductive filament as well as for devices including several conductive filaments. The contribution of each conduction regime has been explained as well as the operation regimes where these ohmic and tunneling conduction processes dominate.

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