Computational modelling of RRAM devices

Resistive Random Access Memories (RRAMs), morphological changes happening within a gap material between two electrodes determine switching between high resistance (HRS) and low resistance states (LRS) to represent the logical "0" and "1". Two types of devices exist: electrochemical metallization cells (ECM) and valence change mechanism cells (VCM). In ECMs, the migration of cations under an applied electric field and their reduction reaction at the inert electrode allows the formation of a conductive filament, achieving the LRS. In VCMs, drift of anions (or their defects) is triggered by a strong internal electric field. When a critical density of defects is reached, oxide breakdown (i.e. LRS) takes place.



RRAMs and are the most promising emerging devices for logic-in-memory operations, scalability, ultra-fast access times, low power consumption, and ease of fabrication. Identifying and understanding ion transport mechanisms that impact endurance and variations in the memristive devices is an important goal which will demolish a significant barrier to the devices widespread application in logic-in-memory architectures, but also uncover crucial science of nanoscale ion movement.



The Di Martino group adopts a novel approach to study optically-accessible memory devices by using plasmon enhanced ultra-concentration of light focussed where material modifications lead to HRS/LRS switching. They correlate the influence on the optical spectrum (dark field scattered light) of the plasmonic hotspot present in the switching junction, tracking as a result the morphological changes occurring in the switching material.

In this project, the student will study materials for applications in resistive memory devices. Dark field and Raman scattering will be analysed to unveil the local morphological changes arising under single nanoparticles which also serve as top electrodes in these plasmonic devices. Computational modelling will provide a solid platform in which to interpret and guide experimental efforts. The student will develop microscopic structural models of the oxides in the presence of various concentrations of oxygen vacancies to reproduce the experimental conditions of operating RRAMs. These structural models will be developed using first principles quantum mechanical calculations based on density functional theory (DFT). The microscopic material models developed will form the basis for the development of a multiscale simulation framework to study the optical properties of these materials during the PhD.