The Paradigm Shift in Understanding the Bias Temperature Instability: From Reaction–Diffusion to Switching Oxide Traps

TLDR

Bias temperature instability (BTI) has been a key CMOS degradation mode since the 1960s, initially attributed to charge trapping and later dominated by a hydrogen‑diffusion reaction–diffusion model, though recovery mechanisms received limited study. This review presents the authors’ perspective on selected developments in BTI research. The authors review the evolution of BTI theories, focusing on recent advances in switching‑oxide‑trap models. Recent studies demonstrate that switching‑oxide‑trap models explain most experimental data, overturning the reaction–diffusion paradigm and refocusing attention on charge trapping.

Abstract

One of the most important degradation modes in CMOS technologies, the bias temperature instability (BTI) has been known since the 1960s. Already in early interpretations, charge trapping in the oxide was considered an important aspect of the degradation. In their 1977 paper, Jeppson and Svensson suggested a hydrogen-diffusion controlled mechanism for the creation of interface states. Their reaction–diffusion model subsequently became the dominant explanation of the phenomenon. While Jeppson and Svensson gave a preliminary study of the recovery of the degradation, this issue received only limited attention for many years. In the last decade, however, a large number of detailed recovery studies have been published, showing clearly that the reaction–diffusion mechanism is inconsistent with the data. As a consequence, the research focus shifted back toward charge trapping. Currently available advanced charge-trapping theories based on switching oxide traps are now able to explain the bulk of the experimental data. We give a review of our perspective on some selected developments in this area.