How does inversed temperature dependence affect timing sign-off

As mainstream processing technology advances into 65 nm and beyond, many factors that were previously considered secondary or insignificant, can now have an impact on chip timing. One of these factor is inversed temperature dependence (ITD). As supply voltage continues scaling into sub-IV territory, delay-temperature relationship can be reversed on some cells, meaning that device switching time may decrease as temperature increases. ITD posts a new challenge for timing sign-off because the highest and lowest sign-off temperatures may no longer be the worst-case and best-case timing corners. This work discuss the effect of ITD and its implication on timing sign-off, based on a standard cell library used in a typical design flow.