Phase-change random access memory: A scalable technology

Abstract

Nonvolatile RAM using resistance contrast in phase-change materials [or phase-change RAM (PCRAM)] is a promising technology for future storage-class memory. However, such a technology can succeed only if it can scale smaller in size, given the increasingly tiny memory cells that are projected for future technology nodes (i.e., generations). We first discuss the critical aspects that may affect the scaling of PCRAM, including materials properties, power consumption during programming and read operations, thermal cross-talk between memory cells, and failure mechanisms. We then discuss experiments that directly address the scaling properties of the phase-change materials themselves, including studies of phase transitions in both nanoparticles and ultrathin films as a function of particle size and film thickness. This work in materials directly motivated the successful creation of a series of prototype PCRAM devices, which have been fabricated and tested at phase-change material cross-sections with extremely small dimensions as low as 3 nm • 20 nm. These device measurements provide a clear demonstration of the excellent scaling potential offered by this technology, and they are also consistent with the scaling behavior predicted by extensive device simulations. Finally, we discuss issues of device integration and cell design, manufacturability, and reliability.

Crystal growth within a phase change memory cell

“…In particular, phase change memory (PCM) has recently emerged as the most promising new nonvolatile solid-state memory technology [1][2][3] . Phase-change materials are also being investigated as building blocks of neuromorphic computing hardware [4][5][6] .…”

Storage-class memory: The next storage system technology

“…In their article in this journal issue, Burr et al [2] provide an overview of SCM candidate device technologies and then compare them in terms of their potential for scaling to ultrahigh areal density [2]. Of the many SCM technologies described in their paper, the one that seems to be in the best position to replace the current flash technology and serve as SCM in the next decade is phasechange memory (PCM) [15,16]. For the remainder of this paper, all numerical estimates are based on the use of PCM.…”

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

“…5,6 Many modern PCRAM cell designs adopt a nanometer-scale hemispherical or cylindrical shape for programing volume to increase the cell density and reduce the operation power. 7 In such device structures, only a portion of the programing volume makes direct contact with a heater electrode, and the other sides are surrounded by passive GST that remains in the crystalline state and acts as an electrical conductivity path during the set and reset switching. One of the critical reliability issues related to these cell structures is the compositional change, or phase separation, caused by electric fieldinduced atomic migration.…”