Today’s stunning computing power is allowing us to move from human intelligence toward artificial intelligence. And as our machines gain more power, they’re becoming not just tools but decision-makers shaping our future.
But with great power comes great…heat!
As nanometer-scale transistors switch at gigahertz speeds, electrons race through circuits, losing energy as heat—which you feel when your laptop or your phone toasts your fingers. As we’ve crammed more and more transistors onto chips, we’ve lost the room to release that heat efficiently. Instead of the heat spreading out quickly across the silicon, which makes it much easier to remove, it builds up to form hot spots, which can be tens of degrees warmer than the rest of the chip. That extreme heat forces systems to throttle the performance of CPUs and GPUs to avoid degrading the chips.
In other words, what began as a quest for miniaturization has turned into a battle against thermal energy. This challenge extends across all electronics. In computing, high-performance processors demand ever-increasing power densities. (New Nvidia GPU B300 servers will consume nearly 15 kilowatts of power.) In communication, both digital and analog systems push transistors to deliver more power for stronger signals and faster data rates. In the power electronics used for energy conversion and distribution, efficiency gains are being countered by thermal constraints.
The ability to grow large-grained polycrystalline diamond at low temperature led to a new way to combat heat in transistors. Mohamadali Malakoutian
Rather than allowing heat to build up, what if we could spread it out right from the start, inside the chip?—diluting it like a cup of boiling water dropped into a swimming pool. Spreading out the heat would lower the temperature of the most critical devices and circuits and let the other time-tested cooling technologies work more efficiently. To do that, we’d have to introduce a highly thermally conductive material inside the IC, mere nanometers from the transistors, without messing up any of their very precise and sensitive properties. Enter an unexpected material—diamond.
In some ways, diamond is ideal. It’s one of the most thermally conductive materials on the planet—many times more efficient than copper—yet it’s also electrically insulating. However, integrating it into chips is tricky: Until recently we knew how to grow it only at circuit-slagging temperatures in excess of 1,000 °C.
But my research group at Stanford University has managed what seemed impossible. We can now grow a form of diamond suitable for spreading heat, directly atop semiconductor devices at low enough temperatures that even the most delicate interconnects inside advanced chips will survive. To be clear, this isn’t the kind of diamond you see in jewelry, which is a large single crystal. Our diamonds are a polycrystalline coating no more than a couple of micrometers thick.
The potential benefits could be huge. In some of our earliest gallium-nitride radio-frequency transistors, the addition of diamond dropped the device temperature by more than 50 °C. At the lower temperature, the transistors amplified X-band radio signals five times as well as before. We think our diamond will be even more important for advanced CMOS chips. Researchers predict that upcoming chipmaking technologies could make hot spots almost 10 °C hotter [see , “Future Chips Will Be Hotter Than Ever”, in this issue]. That’s probably why our research is drawing intense interest from the chip industry, including Applied Materials, Samsung, and TSMC. If our work continues to succeed as it has, heat will become a far less onerous constraint in CMOS and other electronics too.
Where Heat Begins and Ends in Chips
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