At 77k to get a true power advantage you need to consider the costs of the cooling, but thermal density then becomes the limit for computational density as liquids such as nitrogen are more efficient conductors of heat. That means you can build smaller data centres and the communication systems can scale as the computing gets more dense, so there are a number of additional benefits that are orthogonal to the thermal energy consumption, he says.
“We believe paying for more cooling cost to improve the compute density is a key way forward,” he said. “At 4K there’s 10,000x boost in performance for a 100x increase in power consumption.”
The research projects are looking at how these environments can work together.
“Our primary work is communication from the 4K to more conventional CMOS at 77K so its about escaping the 4K environment – we are getting more exposure to the superconducting process and materials and experimenting there but the primary work is communicating with the 4K system.
“The first challenge is that superconducting processors are very low energy,” he said. ”A 2mV pulse for example is a picosecond or so, and there’s really no easy way to receive that with CMOS, so there’s some amplification and material science needed. This has to use really advanced signalling technologies from high speed SERDES with differential forward feedback and error correction and DSP-like technologies to communicate between the 4K device and CMOS.”
“Getting all the CMOS to work reliably at 77K is the second big problem,” he said. “We are partnering to help develop DRAM technologies that operate at this temperature and logic processes so we are developing process files for how a conventional technology can be used. It’s essentially a new PDK [process design kit] for conventional processors so it’s characterising the processors for these temperatures.”
Any digital function translates well, but the problems come with the analogue functions which don’t work as they used to, so the PLLs and mixed signal paths needs to be redesigned. “We haven’t found anything that can’t be done but there are some aspects of regulators and voltage generation that cannot lock or regulate correctly, it just requires a different point on the design curve,” he said.