Dynamic life-estimation of CMOS ICs in real operating environment : Precise electrical method and MLE

The functionality of IC in field use can be maintained by replacing an IC shortly before its anticipated failure. An accurate estimation of circuit lifetime is important in selecting a replacement time to: 1) avoid unanticipated circuit failure by replacing them as early as possible; and 2) use the IC fully by replacing them as late as possible. Since the problem is different from lifetime estimation with accelerated test results, this approach continually measures circuit performance and then analyzes the measurements statistically. The whole estimation process is covered from selection of circuit parameters for performance measurement to development of an aging model for the statistical analysis. The circuit-delay change due to hot-carrier effects is selected to quantify the performance degradation; an aging model, founded on the hot-carrier induced failure mechanism, is developed. Maximum likelihood estimation (MLE) is used for the statistical characteristics of future aging, where the severity of the operating environment is assumed to be a stationary random process. The MLE are used to choose an efficient time for IC replacement. The practical use of the suggested method in IC maintenance is demonstrated with statistically simulated data.