Assessment of Reliability Impact on GHz Processors with Moderate Overdrive

Mitsuhiko Igarashi,  Hideki Aono,  Hideaki Abe,  Koji Shibutani,  Kan Takeuchi
Renesas Electronics Corporation


We showed the effect of power reduction by using moderate VDD overdriving at high temperature conditions. Then moderate overdrive of the supply voltage enables GHz design overcoming thermal runaway. Some issues which alleviate the reliability difficulty in overdrive were discussed. We examined measurement results of NBTI degradation in the high temperature and voltage acceleration test on 45nm products. Although chip-by-chip VDDmin degradation has large variations, it is found that the distribution of VDDmin does not become broader after stress. This comes from slightly negative correlation between initial VDDmin and the degradation, ΔVDDmin. Consequently, we can employ smaller voltage guard-band before shipping than that taking all the large variation of ΔVDDmin into consideration. We also showed that the increase in the voltage guard-band by using overdrive is small enough compared to the overdrive voltage. The max-transition design will become more effective way to improve HCI reliability in advanced process technology because AC-to-DC ratio becomes more strongly dependent on the inverse of output transitions. These findings enable more flexible low-power design including moderate overdrive of supply voltage while sustaining reliability.