The development of metal oxide based resistive random-access memory is of the greatest importance for creating a new class of memory in various applications, including large-scale memory arrays, analogue neuromorphic computing systems, and energy-efficient system-on-chips. The filamentary switching mechanism of resistive memory provides great scalability, while its nonvolatility, energy efficiency, high retention, and write/erase speeds make resistive memory a prospective universal memory. The ability of resistive memory to mimic the behavior of biological synapses coupled with its multilevel storage capabilities makes this novel type of memory a suitable hardware for analogue neuromorphic systems. However, practical application for large-volume memory arrays for neuromorphic systems is limited by unresolved fundamental issues including intrinsic cycle-to-cycle variability of a high resistance state and extrinsic cell-to-cell variability of switching from a low to a high resistive state. Mitigation of these issues is impossible without a clear understanding of physical processes occurring inside dielectric layers of resistive memory. In this paper, we address these issues via theoretical and experimental investigation and demonstrate that both issues are related to the formation of multiple conductive filaments.

Resistive random-access memory (RRAM) is a crucial element for next-generation large-scale memory arrays, analogue neuromorphic computing and energy-efficient System-on-Chip applications. For these applications, RRAM elements are arranged into Crossbar arrays, where rectifying selector devices are required for correct read operation of the memory cells. One of the key advantages of RRAM is its high scalability due to the filamentary mechanism of resistive switching, as the cell conductivity is not dependent on the cell area. Thus, a selector device becomes a limiting factor in Crossbar arrays in terms of scalability, as its area exceeds the minimal possible area of an RRAM cell. We propose a tunnel diode selector, which is self-aligned with an RRAM cell and, thus, occupies the same area. In this study, we address the theoretical and modeling aspects of creating a self-aligned selector with optimal parameters to avoid any deterioration of RRAM cell performance. We investigate the possibilities of using a tunnel diode based on single- and double-layer dielectrics and determine their optimal physical properties to be used in an HfOx-based RRAM Crossbar array.