Digital circuits reliability with in-situ monitors in 28nm fully depleted SOI

Aging induced degradation mechanisms occurring in digital circuits are of a greater importance in the latest technologies. Monotonic degradation such as Bias Temperature Instability (BTI) or Hot Carrier Injection (HCI) but also sudden degradation such as Dielectric Breakdown (DB) are identified as the major sources of reliability hazard. The impact of these phenomena on the digital circuits is usually observed in terms of timing degradations and thus may result in setup/hold violation. In this paper we will focus on the impact of aging related degradation mechanisms on timing. In-situ monitor is a promising strategy to measure timing slacks and to provide pre-error warnings prior to timing violation. In this paper, we have developed a dedicated test structure to measure and benchmark the behavior of different monitors. The design of monitors is mostly based on delay elements. Three types of delays are proposed in this paper: flip-flop's Master delay, Buffers delay and Passive delay. In addition, we investigate the impact of global and local variations on the accuracy of the measurements by providing complete monitors characterization. The technology used for the test structure and in-situ monitors is 28nm Fully Depleted Silicon On Insulator. Experimental results show a good agreement with SPICE simulation. Finally the proposed in-situ monitors will be compared and their applications to circuit aging prediction will be discussed.