CMOS-circuit degradation analysis using optical measurement of the substrate current

This paper analyzes the photon emission under AC operation caused by hot carriers in MOSFET's, and determines the lifetime of CMOS circuits by means of a direct photon count measurement that replaces the traditional electrical measurement of the substrate current. This is made possible by the linear relation between the substrate current and the photon count at about 830 nm for all operating values of gate voltage. The paper presents an application of this method to monitor the long term degradation of the delay time of CMOS inverters and highlights the advantages of this noninvasive technique which can therefore be used to predict the lifetime also of devices in which the substrate current cannot be measured directly, as in SOI devices.