Memristive in situ computing

The missing link between a nonlinear circuit element that is able to selfadjust its conductance according to the history of applied voltage/current and physical realizations of two-terminal oxide-based resistive memory was discovered in early 2008, and has since been intensively studied. This class of memory elements is called memristive devices, which includes resistive random access memories (RRAM), phase change memories (PCM) and spin-transfer torque magnetoresistive memories (STT-MRAM). Memristive devices are mostly CMOS and fab friendly, and promise simpler architecture, higher scalability and stackability (3D), good selectivity, relatively low-power consumption, high endurance and retention, fast operation by utilizing parallelism, and the most important of all, the ability to merge logic and memory. A significantly wide range of resistive switching materials can be categorized under three main redox-related effects, electrochemical metalization effects (ECM), valency change memory effect (VCM) and thermochemical memory effects (TCM). Although, the behavior of these resistive memories can be modeled using high-level finite-state machines (FSMs), the underlying switching mechanisms is yet to be fully understood. Despite the lack of comprehensive understanding of the switching behavior, their application in memory and computing has been constantly improved. These devices can be programmed to exhibit multi-level cell (MLC) and binary cell behavior, thus analog and digital memories can be exists in one device depends on programming. In this chapter, we highlight some of the in situ computational capability of memristive devices.