The scanning electron micrograph shows a close-up image of the cooling layer. The so-called pin-fin cooling structure used in this test vehicle performed best in these experiments and achieved an output of 180 Watts/cm2 per layer in a stack with an area of 4 cm2. (Credit: IBM)

Placing chips vertically, rather than side by side, trims down the distance data has to travel, thus improving efficiency and saving critical space. "As we package chips on top of each other, we have found that conventional coolers attached to the back of a chip don't scale," said Thomas Brunschwiler from IBM's Zurich Research Laboratory. "In order to exploit the potential of high-performance 3D chip stacking, we need interlayer cooling," he explained further.

The image shows this interlayer water cooling technique in which the cooling structures are integrated directly into the chip stack. Using a special assembly technique the layers can be connected in a high-precision and robust way that allows water to be pumped through the 3-D stack embedded in a cooling container (purple). (Credit: IBM)

As a result, researchers around the world are actively looking for the most efficient way to remove heat from the chip. In 2007, US scientists developed tiny wind engines that produced a "breeze" which consisted of charged particles, or ions, to cool computer chips. However, heat dissipation problems would be aggravated in IBM’s multi-story chips which are going to be implemented in future processors.

To avoid this, researchers piped water through sealed tubes just 50 microns (millionths of a metre) in diameter, between individual layers. Water is much more effective than air at absorbing heat and with a minute measure of liquid flowing through the system, the researchers saw considerable results. Pumping liquids through computers isn’t new. Early mainframe computers had water pumped around them.

The photo shows a complete view of a single interlayer 3-D cooling prototype before assembly. The active cooling area, the structured area in the center of the prototype, measures 1 by 1 cm, has a height of 100 microns, and contains up to 10,000 vertical interconnects (Credit: IBM)

In 2007 TFOT covered another innovative processor cooling technology based on ionic wind developed by Kronos Advanced Technologies in collaboration with Intel and the University of Washington. TFOT has also previously written about the MIT team who developed an energy efficient microchip, where researchers discovered a way to significantly decrease microchip energy consumption to one tenth of the current rates. TFOT also covered the chip technology of cooler, faster, cheaper silicon chips recently developed using a new process and equipment that is expected to significantly reduce the amount of heat generated by silicon chips used for speeding processors.

Additional information of IBM’s water cooling system for 3-D chips can be found on IBM’s website.