When desktop processors first broke through 1GHz, it seemed for a while that there was nowhere to go. At first, it was possible to raise the frequency due to new technical processes, but the progress of frequencies eventually slowed down due to the growing requirements for heat removal. Even massive heatsinks and fans sometimes do not have time to remove heat from the most powerful chips.
Researchers from Switzerland decided to try by passing liquid through the crystal itself. They designed the chip and cooling system as a single unit, with the liquid channels on the chip placed near the hottest parts of the chip. The result is an impressive increase in performance with efficient heat dissipation.
Part of the problem with heat dissipation from the chip is that it usually involves several stages: heat is removed from the chip to the package of the chip, then from the package to the heatsink, and then to the air (thermal paste, evaporation chambers, etc. Further). In sum, this limits the amount of heat that can be removed from the chip. This is also true for the liquid cooling systems currently in use. It would be possible to place the chip directly in a heat-conducting liquid, but the latter should not conduct electricity and enter into chemical reactions with electronic components.
There have already been several demonstrations of liquid cooling built into the chip. Usually we are talking about a system in which a device with a set of channels for liquid is welded onto a crystal, and the liquid itself is pumped through it by pumps. This allows you to efficiently remove heat from the chip, but initial implementations showed that there is a lot of pressure in the channels and pumping water in this way requires a lot of energy - more than is removed from the processor. This reduces the energy efficiency of the system and, in addition, creates dangerous mechanical stresses on the chip.
A new study develops ideas for improving the efficiency of on-chip cooling systems. For the solution, three-dimensional cooling systems can be used - microchannels with an embedded manifold (embedded manifold microchannels, EMMC). In them, a three-dimensional hierarchical manifold is a component of a channel that has several ports for distributing coolant.
The researchers developed a monolithically integrated manifold microchannel (mMMC) by integrating EMMC directly onto the chip. Hidden channels are built right under the active areas of the chip, and the coolant passes directly under the heat sources. To create mMMS, narrow slots for channels are first etched on a silicon substrate coated with a semiconductor, gallium nitride (GaN); then, isotropic gas etching is applied to widen the slots in the silicon to the desired channel width; after that, the holes in the GaN layer over the channels are sealed with copper. The chip can be fabricated in a GaN layer. Such a process does not require a connection system between the collector and the device.
Researchers have implemented a power electronic module that converts alternating current to direct current. With its help, heat fluxes of more than 1,7 kW/cm2 can be cooled using a pumping power of only 0,57 W/cm2. In addition, the system exhibits much higher conversion efficiency than a similar uncooled device due to the lack of self-heating.
However, one should not expect the imminent appearance of GaN-based chips with an integrated cooling system - a number of fundamental issues have yet to be resolved, such as system stability, temperature limits, and so on. And yet, it is a significant step forward towards a brighter and colder future.
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Source: 3dnews.ru