What are the thermal issues of modern SoCs?
Gate density has been increasing with each node and that pushes up power per unit area. This has become an even more significant issue with FinFET processes, where the channels are more thermally isolated than planar processes before them.
Then there is leakage, which in the last few planar nodes was an issue that led to significant power consumption. That has been pegged back somewhat with the latest FinFET nodes but it will continue to be an issue going forward as we look toward the next generation FinFET nodes and beyond.
In addition to these issues, if you are developing for consumer products, smartphones, tablets, that kind of thing then you are always limited in terms of how much heat you can dissipate because you don’t have active cooling systems such as fans, and obviously the upper temperature limit of the product is quite low. In addition, the hotter things get the bigger the issue of reliability and lifetime of device parts which is perhaps the biggest issue going forward, as we are then talking about electro-migration, hot carriers, and BTI effects which we have discussed in the past.
How hot is hot?
That all depends on the application! That said, one thing that is interesting now with the growth in automotive applications, such as ADAS and infotainment is we are starting to see that even 125°C is not high enough as those markets demand higher temperature operation. So for those applications hot is hotter than it may be for say a consumer device where 40°C for the product might be your limit. Then there will be a thermal mass to factor in so you will have devices within that product which are much hotter.
But the key thing for our customers is knowing device temperature accurately. The more accurately they know the temperature the closer to the limit they can operate. That is really what it is all about for modern SoCs; being as close as you can to the limit without stepping over it. And because temperature has an exponential effect in terms of ageing, the accuracy of temperature sensors is correspondingly important.