Things are getting a bit too hot in the microprocessor world. Again.
Moore’s Law has always come with the caveat that more transistors, switched at a higher frequency, means more heat. Over the years, chipmakers have used tricks like throttling back clock speeds and putting multiple microprocessor cores on a chip to spread out the heat.
But heat continues to stifle chip performance. Hot spots on today’s processors can reach power densities of 1 kilowatt per square centimeter, much higher than the heat inside a rocket nozzle. A growing fraction of transistors on advanced microprocessors are not even operated at any one time because they would generate too much heat, says Avram Bar-Cohen, a program manager at the microsystems technology office of DARPA. “As we put more and more transistors on them, this ‘dark silicon’ fraction has gone from 10 to 20 percent, in some cases more,” he says.
There’s only so much that processor designers can do to keep chips from generating too much heat, and it’s time for some new ways to get that heat out.
The conventional approach to dissipating the heat is to attach the silicon die to a copper or aluminum block carved with elaborate fins and ridges. A plastic fan blows air across the metal. As you can guess, these systems can be bulky, noisy, and power hungry.
Plus, heat sinks and fans won’t cut it for future processors, which will be 3-D stacks of ICs. Such layering can trap heat between chips, making getting rid of it even harder.
Researchers are exploring better ways to cool chips and gadgets, either by redesigning tried-and-tested methods or drastically overhauling them. The challenge for all of these technologies is whether the semiconductor industry will be ready to integrate them, says Ravi Prasher, a director in the energy technologies division at Lawrence Berkeley National Laboratory, in California, who has studied various chip-cooling technologies.
Here’s a look at some methods that could beat the heat.
