Lifetime Estimation Using Ring Oscillators for Prediction in FinFET Technology

Lifetime testing of circuits is challenging because of the need to design circuit-specific test structures and test patterns. The goal of this work is to find a ring oscillator that matches a circuit’s wearout behavior limited by time-dependent dielectric breakdown (TDDB), electromigration (EM), and stress-induced voiding (SIV) lifetime distributions, which can be used to foreworn circuit breakdown. The equivalent ring oscillator is easier to test, enabling the collection of more experimental lifetime data. Therefore, this paper aims to find the appropriate ring oscillator for a target circuit by mapping the lifetime of a circuit to a ring oscillator using analytical equations that involve layout parameters (area, length, width of device and interconnect) and operating conditions (supply voltage, temperature, probability of stress, current). Practical ring oscillator equations for lifetime estimation were derived, which describe relationships between stage number, oscillation frequency, characteristic lifetime, and Weibull parameters. The methodology is illustrated with example circuits that were implemented with 14nm FinFET technology.