Impact of Random Soft Oxide Breakdown on SRAM Energy/Delay Drift

Reliability issues have been traditionally considered only for functional yield problems. Among them, the progressive gate-oxide soft breakdown (SBD) in the negative-channel field-effect transistors is foreseen to be a big issue for the deep-deep submicron technologies, where ultrathin gate oxide and low supply (stress) voltage will be massively deployed. Device-level investigation has largely confirmed that the SBD defect will not lead to an issue for the transistor functionality. In addition, simple gate-level characterization also indicates that the SBD defect in those gates only leads to performance degradation. Up to now, the impact of the random nature with such effect is not yet well understood at a complex circuit block or component level. In this paper, we have focused our analysis in providing insights on the SBD impact on sensitive static random access memory (SRAM) components as well as the complete matrix. Results have shown a significant shift in the performance figures of the blocks, which endangers the SRAM parametric yield. The drift becomes even worse when the process variability effect is taken into account. All the results indicate urgent needs to develop effective countermeasures by both the technology and design sides.