This innovation, the researchers report, can achieve a significant increase in performance. The scientists have also integrated passive components for voltage regulators, photonic ICs and optical waveguides into the interposer.
Up until now, cooling elements have been used to avoid overheating, while, at the same time, fans are used to cool the heat-sensitive components from above. A research team led by Dr. Wolfram Steller, Dr. Hermann Oppermann and Dr. Jessika Kleff from the Fraunhofer Institute for Reliability and Microintegration IZM, in Berlin and Dresden, has now found a way to cool microchips from both top and bottom, using a liquid-based cooling system. This allows more effective cooling and therefore higher performance. For this purpose, microchannel structures with hermetically sealed vias are installed in the silicon interposer, which is located between the processor and the printed circuit board. The coolant is then pumped through the microchannels, taking heat away from the processor.
Interposers are responsible for the electrical supply and cooling of the processor; a layer between the circuit board and the chip and, that is equipped, every 200 micrometres, with electrical contacts to ensure the processor’s power supply and data transmission. In order to be able to absorb heat and channel it away from the processor, the scientists at Fraunhofer IZM created microfluid channels cross-linking the vias, allowing coolant to be circulated.
The particular challenge was not only to integrate the small channels into the interposer, but also to hermetically seal them and thus to separate them from the electrical paths. The solution the scientists arrived at is that the interposer is made of two silicon plates. Horizontally-oriented cooling channels, as well as the vertically-oriented channels for the electrical lines are incorporated in a complementary manner. In order to prevent contact between the water and the electrical vias, each individual contact is specially sealed.