Reliability assessment based on accelerated degradation: a case study

An analysis strategy (experimental and analytic) for extracting reliability information from the measured degradation of devices subjected to elevated stress is described. The strategy is applied to the estimation of the reliability of an integrated logic family that is a component of a new generation of submarine cables. The experiment consisted of monitoring several electrical parameters while aging the devices under elevated temperature. The authors model changes observed in one of these electrical parameters (propagation delay) and identify and quantify various sources of variability observed in the data. These models are used to predict (with 95% confidence) that a randomly selected device operating at 40°C will see a change of no more than 2 ns in propagation delay in 25 yr, the lifetime of a submarine cable. An analysis of the degradation rate leads to the conjecture that the observed change in propagation delay is due to the diffusion of impurities (Na) through the bulk of the oxide layer (SiO₂)