NBTI-Aware Power Gating Design with Dynamically Varying Stress Probability Control on Sleep Transistor

With the aggressive scaling of the transistor, Negative Bias Temperature Instability (NBTI) has become the most dominant aging effect which causes the device parameter to degrade over its lifetime. This device parameter degradation of logic gates in nanometer technology is a major concern for the reliability of the digital circuit. It becomes even more critical when it comes to power gating structure, as small NBTI effect on PMOS sleep transistor used in header-based power gating structure would seriously affect the reliability, performance of the whole logic circuit. The conventional method of mitigating the NBTI effect is to oversize the sleep transistor, but it also gives rise to leakage overhead. In this work, a novel NBTI aware power gating architecture is presented to improve the lifetime of the circuit. Here, sleep transistors (STs) are switched ON/OFF periodically and a greater number of STs are turned ON, when NBTI related degradation reaches to its threshold value so that STs get more time to anneal NBTI degradation and improve its lifetime. Simulation result on ISCAS’85 benchmark circuits shows for 40% sleep signal, an average of 51.2% and 14% lifetime improvement with respect to the conventional over-sizing (OS) technique and normal stress probability control method, respectively with some power and area overhead.