Re-investigating the adequacy of projecting ring oscillator frequency shift from device level degradation

One of the major purposes of evaluating discrete device reliability is to provide aging predictions of a circuit. Since ring oscillator (RO) is a key substitute for fast switching circuits due to its simplicity and coverage. It is, therefore, necessary and fundamental to have an accurate frequency shift simulation of RO from a discrete device based model. (An accurate frequency shift simulation of RO based on a discrete device reliability model can´t be stressed enough.) In this study, correlation between single device degradation and frequency shift of high-k/metal-gate (HK/MG) RO is discussed. Commonly used I_dsat or V_t failure criteria at device level are found inappropriate to predict aging effects on RO. Thus, a simple and accurate methodology is proposed to bridge this gap. Due to the complexity and diversity in real circuits, RO itself is worthy of being an indispensable test pattern during process development.