Radiation Induced Charge Loss Mechanisms Across the Dielectrics of Floating Gate Flash Memories

Abstract

One of the key factors permitting the extraordinary success of floating gate (FG) nonvolatile memories relies on the excellent insulating properties of the dielectric layers surrounding the FG itself. Among other threats, ionizing radiation may effectively affect such insulating characteristics, leading to a degradation of the FG stored charge. Radiation effects have been traditionally studied for niche applications such as the high energy physics or the satellite industry. However, modern semiconductor technologies are becoming more and more sensitive to the deposition of small amounts of charge, such as those generated by the byproducts of atmospheric neutrons, and FG memories are in fact aggressively scaled following Moore's law predictions. Loss of information may derive from two broad categories of phenomena, Total Ionizing Dose and Single Event Effect, whose actions on the FG dielectrics are reviewed in this contribution from the viewpoints of the prompt induced damage and long-term degradation effects, affecting the memory retention capabilities.