A group of researchers has developed a new approach to electronic cooling, one which uses liquid cooling channels integrated directly into semiconductor chips. Unlike previous microfluidic channel approaches, the research focused on codesigning the electronics and cooling channels within the same semiconductor substrate. The result, according to the research paper in Nature, is “a monolithically integrated manifold microchannel cooling structure with efficiency beyond what is currently available.”
Microchannel cooling technology was first proposed in 1981, but even state-of-the-art solutions today suffer a drawback: the cooling systems are still developed separately and then bonded to the chip afterward. The bonding layer itself contributes added heat resistance.
Researcher Elison Matioli shared that the team designed both the electronics and the cooling together from the beginning. “We take it to the next level,” said Matioli.
The microfluidic cooling channels are designed to fit under the active region of a transistor device, where it’s liable to heat up the most. To create the integrated device, the researched etched micrometer-wide slits—30µm long and 115µm deep—on a gallium nitride layer coated on the silicon substrate. A special gas etching technique is used to widen the slits in order to form the channels where the liquid coolant will be pumped. The slits are then sealed with copper before the rest of the chip is completed.
“We only have microchannels on the tiny region of wafer that’s in contact with each transistor,” said Matioli. “That makes the technique efficient because we can extract a lot of heat due to proximity but we use very little pumping power.”
The researchers demonstrated the technology by creating an AC-to-DC rectifier circuit with four Schottky diodes, each with a 1.2 kV capacity. This kind of device would typically be coupled with a large heat sink, not necessary with the application of the microfluidic channels.
The hot spots on the chip exhibited power densities of over 1,700 W/cm2. The microfluidic cooling channels were able to cool the chip using only 0.57 W/cm2 of pumping power, which is a50 times increase in cooling performance compared to existing micro cooling channels.
The best potential application of the new cooling approach is in power electronics, according to electronics cooling researcher Tiwei Wei, who adds that the reliability of the combination of gallium nitride and copper should still be investigated.
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