Physics and modeling of transistor matching degradation under matched external stress

In this paper, we report detailed studies on transistor matching reliability under external stresses such as NBTI. Transistor threshold voltage VT mismatching as a function of stress voltage, ambient temperature as well as stress time has been established based on device physics and statistics. A closed form equation for current mismatching under stress has also been obtained using a correlated mobility-shift and VT-shift model. Methods to extract relevant parameters in the models have been established. The models have been validated experimentally and been used to predict the transistor matching shift under normal operating conditions for a 40V high performance precision analog technology. It has been found that transistor matching degrades ~10% during the 10 years lifetime of products when operating at VGS=15V and 100C. This suggests ~10% over design for critical matched transistors at time zero in order to achieve a 10 year reliability requirement.