Chapter 2 - Resistive switching memories

Abstract

This chapter gives a general overview of the state-of-the-art of resistive switching random access memories (RRAM or ReRAM), which are metal/insulator/metal devices exhibiting resistance transition upon voltage application. They are also classified under the name of memristors or memristive devices. This chapter starts with an introduction to the various physical mechanisms, in relation to material science aspects, which produce resistance switching, including redox processes, ionic migration, metal–insulator phase transitions, conductive filament formation/dissolution, and metal/insulator barrier modifications. The presented physical mechanisms drive different macroscopic electric behavior (nonpolar and bipolar, volatile, and nonvolatile switching) with diverse performances, opportunities, and limitations. A specific section is dedicated to all these aspects and to the overview of the state-of-the-art of industrial-level demonstrations and products, with particular reference to the nonvolatile memory application. Furthermore, this chapter describes the current research lines aiming at augmenting the device functionality. The physical foundation and the typical material selection toward multilevel capability, plasticity, pulse rate– and pulse timing–dependent switching, and negative differential resistance are presented.