A self-consistent model to estimate NBTI degradation and a comprehensive on-line system lifetime enhancement technique

Lifetime reliability and the resultant temporal performance degradation due to Negative Bias Temperature Instability (NBTI) has emerged as a critical challenge in design and test of integrated circuits in nanometer technology nodes. In this work, we have developed a model that self-consistently estimates the NBTI degradation by considering the impact on the circuit lifetime of inter-dependent parameters such as V_dd and temperature simultaneously. Using the proposed model, we observed that a circuit with lower V_dd can provide better lifetime performance than with higher V_dd. This interesting observation can be attributed to the reduction of electric field in the transistor along with the circuit power/temperature reduction that leads to lesser NBTI degradation. Based on this observation we have developed a on-line detection and mitigation scheme that allows V_dd scaling to enhance system lifetime. The proposed scheme was applied to various arithmetic units and results in 45nm IBM process technology show 18% lifetime improvement with 57% reduction in power compared to conventional mitigation techniques. We also show that by using existing NBTI estimation models, the error in delay estimation can be as large as 7.6%.