A radiator on the chip?

Liquid ports carry cooling water to specially designed passages etched into the backs of FPGA devices to provide more effective cooling. The liquid cooling provides a significant advantage in computing throughput. Credit: Rob Felt/Georgia Tech

The second law of thermodynamics is there to remember us that whatever we are doing we end up creating heat. And unless your goal is to fry potato chips you need to find ways to dissipate that heat to keep the temperature within a workable range.

Chips, not potato chip but electronic chips, are suffering from heat accumulation and engineers have found ways to dissipate this heat. They use fans, they make sure to position chips not too close one another to let natural air flow cool them, they place dissipating cold metal plates on the chip surface...

The more transistors you have in a chip the more heat is being produced. By reducing the voltage and by keeping the activities below a certain rate (decreasing the Hz... clocking the transistors) engineers have managed to keep the heat within the possibility of dissipating it. 

Reducing voltage is something that you can do as you shrink the size of the transistor, and it is fine. The problem is that as you shrink the size of the transistor you place more transistors on any given area, density increases, and hence the heat production increases. Decreasing the chip speed, the clock, you are decreasing its performances and this is not good...

Liquid cooling is already being used to cool metal dissipation layers glued on the chip upper surface.  Now, a team at the Georgia Institute of Technology have managed to create a much more efficient liquid cooling system.

Rather than using the liquid coolant to cool the metal layer on the chip they have created microscopic channels by etching the surface of the chip and then have glued the pipes carrying the coolant to the chip. The technology used is the one of microfluidic, a way to carry micro flows of liquid in very tiny pipes.  They have shown that by "flowing" the etched chip surface with purified water (they removed all ions to avoid any electrical problem) at a temperature of 20°C the chip operated at 24°C. For comparison that same chip being cooled with free flowing air would operate at 60°C.

This new approach is so effective because the coolant goes to a few microns from the surface of the transistors and can hence remove the heat generated without having it accumulating in the chip.

A colder chip is a chip that can run at higher clock speed (it would heat up more of course, but it will remain within the operation specs) and it is also a chip that will have a significantly longer life time.

The interest of this method is that it can be applied to existing chips since the etching on their surface is done after they have been manufactured, it does not require any change in manufacturing.

Of course the goal of chip designers remain to have chips that do not need any cooling, and that is more and more feasible in many cases but where there is need for high performance a cooling of some sort is required.

Author - Roberto Saracco

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