The third article in the Moortec “Let’s Talk PVT Monitoring” series with Moortec CTO Oliver King about thermal issues associated with modern SoCs - How Hot is Hot? As Moortec’s CTO, Oliver has been leading the development of compelling in-chip monitoring solutions to address problems associated with ever-shrinking System-on-Chip (SoC) process geometries. Moortec have been tackling the issue presented by complex, multi-core processor System on Chip (SoC) designs, which although enabling a marketplace of compelling electronic products attractive to the consumer, do however come with some very real challenges. Developers of advanced node devices, on technologies such as 28-nm and FinFET, are becoming increasingly aware of the issues of heat, voltage supply and variations within the manufacturing process. To tackle these issues, Moortec provide process, voltage and temperature (PVT) monitoring IP solutions that are embedded within SoC designs. The on-chip monitors allow for dynamic performance optimization, as sensing die temperature, detecting logic speed and monitoring voltage supply levels can be used intelligently to vary system clock frequencies and the voltage levels of supply domains.

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Moortec “Let’s Talk PVT Monitoring” Series with CTO Oliver King
By Ramsay Allen
Thermal Issues Associated with Modern SoCs - How Hot is Hot?
17th June 2016
In this, the third instalment of the "Let's Talk PVT Monitoring" series
Moortec CTO, Oliver King talks about the thermal issues associated
with modern SoCs and ponders the question How Hot is Hot? Oliver has
been leading the development of compelling in-chip monitoring
solutions to address problems associated with ever-shrinking System-
on-Chip (SoC) process geometries. An analogue and mixed signal design
engineer with over a decade of experience in low power design, Oliver
is now heading up the expansion of Moortec's IP portfolio into new
products on advanced nodes.
Questions:
1. 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.
2. 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.
Moortec CTO, Oliver King

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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.
3. Trend in use
Certainly a number of years ago when we started developing temperature sensors, they
were being used generally just for device characterisation, HTOL, burn in tests and those
kind of things. Then they started to be used for high temperature alarms, either to switch
off the device or turn on a fan. But we have seen over the last couple of years more
applications which rely on these monitors. Applications like Dynamic Voltage and Frequency
Scaling (DVFS), Adaptive Voltage Scaling (AVS) and lifetime reliability. These applications
make use of the sensor data in a feedback control loop. So certainly the use cases now are
much more varied.
The trend for the recent past has been driven by consumer electronics and in those cases
you are really trying to get a lot out of a device whilst not making it too hot, because it’s in
your pocket, or its on your lap or whatever, so this has driven the use cases. I believe that
we are moving into a space where just the cost of the advanced node technologies mean
you want to get everything out of a device , and all of the different levels of over design that
are added to the process, the design flow, take away performance. As a result, having
sensors on chip, whether they are temperature sensors, or process or voltage allow you to
get that little more performance out of your device and, or improve reliability.
4. What requirements does that place on temperature sensors?
The most important thing from where we sit is accuracy. The greater the uncertainty in the
measured result, the less you can do with it. So for us the key motivation is accuracy. But
beyond that the next thing is robustness and testability, because you are now using these
sensors in application areas where their failure can cause system failure. This means you
need to be able to test them, you need to be able to rely on them. So we are doing a lot in
that sense to ensure that there is testability and there is robustness in our products.
5. How does Moortec address those requirements?
The first thing is that we meet the accuracy requirements and we aim to exceed them. In
terms of testability and robustness we have done a lot of work to be able to provide online
fault detection and diagnosis of our sensors.

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This means you can interrogate them and understand if there is a fault. Firstly, it will tell you
if there is a fault, and secondly you can then ask it what is wrong and it can give you certain
amount of health diagnosis. In addition, we support scan chains to increase overall test
coverage.
Then on top of that we believe ease of integration is an important factor. Not because it
gives you a more accurate temperature sensor, but to make it easier for the customer to
implement and use the product.
About the interviewee
Oliver King is the Chief Technology Officer of Moortec Semiconductor. Before joining
Moortec in 2012, Oliver was part of the analogue design methodology team at Dialog
Semiconductor and prior to that was a senior design engineer at Toumaz Technology. Oliver
graduated from The University of Surrey in 2003 with a degree in Electrical and Electronic
Engineering.
About Moortec Semiconductor
Moortec Semiconductor, established in 2005, provide high quality analog and mixed-signal
Intellectual Property (IP) solutions world-wide specialising in die monitoring. Having a track
record of delivery to tier-1 semiconductor and product companies, Moortec provide a quick
and efficient path to market for customer products and innovations. For more information,
please visit www.moortec.com.
Contact: Ramsay Allen, +44 1752 875133, ramsay.allen@moortec.com