Modern high-performance chips are marvels of engineering, containing tens of billions of transistors. The problem is, you can’t use them all at once. If you did, you would create hot spots—high temperatures concentrated in tiny areas—with power densities nearing those found at the surface of the sun. This has led to a frustrating paradox known as dark silicon, a term coined by computer architects to describe the growing portion of a chip that must be kept powered down. Up to 80 percent of the transistors on a modern chip must remain “dark” at any given moment to keep the chip from sizzling. We are building supercomputers on a sliver of silicon but only using a fraction of their potential. It’s like building a skyscraper and being able to use only the first 10 floors.
For years, the industry has battled this thermal limit with bigger fans and more complex liquid cooling systems. But these are fundamentally Band-Aid solutions. Whether using air or liquid, they rely on pulling heat away from the chip’s surface. The heat must first conduct through the silicon to the cooling plate, creating a thermal bottleneck that simply cannot be overcome at the power densities of future chips. Hot spots on today’s chips produce tens of watts per square millimeter, and they pop up in various places on the chip at different times during computations. Air and liquid cooling struggle to focus their efforts at just the hot spots, when and where they appear—they can only try to cool the whole thing en masse.
We at St. Paul, Minn.–based startup Maxwell Labs are proposing a radical new approach: What if, instead of just moving heat, you could make it disappear? The technology, which we call photonic cooling, is capable of converting heat directly into light—cooling the chip from the inside out. The energy can then be recovered and recycled back into useful electric power. With this approach, instead of cooling the whole chip uniformly, we can target hot spots as they form, with laser precision. Fundamentally, this technique could cool hot spots of thousands of watts per square millimeter, orders of magnitude better than today’s chips are cooled.
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