Nowadays, the heat generated by dense electronic equipment is an expensive resource consumption. In order to keep the system at the right temperature for optimal computing performance, the cooling system in the United States consumes as much energy and water as all residents of Philadelphia. Now, by integrating the liquid cooling channel directly into the semiconductor chip, researchers hope to at least reduce this loss in power electronic equipment, making it smaller, lower cost, and lower energy consumption.
Traditionally, electronic devices and thermal management systems are designed and manufactured separately, says Elison Matioli, professor of electrical engineering at the Ecole Institute of Technology in Lausanne, Switzerland. This brings a fundamental obstacle to improving cooling efficiency, because heat must travel a relatively long distance in multiple materials to be removed. For example, in today's processors, thermal material siphons transfer heat from the chip to the bulky air-cooled copper heat sink.
In order to obtain a more energy-efficient solution, Matioli and his colleagues developed a low-cost process that puts the 3D network of microfluidic cooling channels directly into the semiconductor chip. Liquid can remove heat better than air. The idea is to keep the coolant micrometer away from the hot spots of the chip.
But unlike the previously reported microfluidic cooling technology, he said: "We design electronic devices and cooling systems from the beginning." Therefore, the microchannel is located below the active area of each transistor device, where its temperature The highest, which increases the cooling performance by 50 times. They reported their common design concept in the recent "Nature" magazine.
Researchers have proposed micro-channel cooling technology as early as 1981, and start-up companies such as Cooligy have also been pursuing the concept of processors. However, the semiconductor industry is shifting from planar devices to three-dimensional devices, and is moving towards future chips with multilayer structures, which makes cooling channels impractical. "This kind of embedded cooling solution is not suitable for modern processors and chips, such as CPUs," said Tiwei Wei, who studies electronic cooling solutions at Interuniversity Microelectronics Center and KU Luuven in Belgium. "On the contrary, this kind of cooling technology makes the most sense for power electronics," he said.
Power electronic circuits manage and convert electrical energy, which are widely used in fields such as computers, data centers, solar panels, and electric vehicles. They used large-area discrete devices made of wide-bandgap semiconductors such as gallium nitride. The power density of these devices has risen sharply in the past few years, which means that they must be "hooked up with a huge heat sink," Matoli said.
Recently, power electronic modules have turned to liquid cooling, whether through cold plates or micro-channel cooling systems. However, to date, all micro-channel cooling systems have been manufactured separately and then combined with chips. The bonding layer increases heat resistance, and the channel and the circuit device are not closely aligned.
"We took it to the next level," Matoli said, by manufacturing equipment and cooling channels in the same chip. They etched micron-wide cracks in the gallium nitride layer coated on the silicon substrate. The slit is 30μm long and 115μm deep. Using special gas etching technology, they widen the gap on the silicon substrate to form a channel through which the liquid coolant passes.
Then, the researchers used copper to seal the tiny openings in the gallium nitride layer and fabricated devices on it. He said: "We only have microchannels in tiny areas of the wafer, and these microchannels have contact with every transistor. This makes this technology more effective because we can extract a lot of heat from nearby, but the pumping we use The power is very small."
As a demonstration, the researchers made an AC-DC rectifier circuit composed of four Schottky diodes, each diode can handle a voltage of 1.2kV, a circuit like this usually requires a fist-sized heat sink. But the circuit chip integrated with the liquid cooling system is mounted on a printed circuit board the size of a USB flash drive. The circuit board consists of three layers with channels engraved on it to deliver the cooling liquid to the chip.
The display shows that hot spots with a power density of more than 1700 W/cm² can be cooled by only 0.57 W/cm² pumping power. Compared with the previously reported microfluidic channel cooling, the performance is improved by 50 times.
Wei said, "The reliability of gallium nitride film and copper sealing layer should be studied over time. But this innovative cooling solution is a step towards a "low-cost, ultra-compact and energy-saving power electronic cooling system." A big step forward."
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