On-Chip Liquid Cooling With Integrated Pump Technology

In this paper, the capability of a novel cooling system for microchannels based on the principle of electrowetting is examined. To start with, the elcctrowetting effect in microchannels is experimentally investigated. The used electrowetting system consists of a liquid droplet deposited on a conductive Si substrate and electrically insulated from this substrate by a dielectric, layer. Microchannels of 100 mum times 100 mum are etched in the substrate. By applying an ac voltage signal between the droplet and the substrate, the microchannels can be periodically tilled and emptied with the liquid of the droplet. This oscillating liquid flow will be used to cool the chip. For the 100 mum times 100 mum microchannels a voltage of 51 V is required for the actuation. Further, based upon the results of the filling of the channels the cooling capacity of the proposed system is theoretically investigated. The theoretically achievable cooling rate of this enhanced system is compared to the heat transfer by conduction through a silicon substrate. A critical filing period is found; for shorter filling periods, the heat transfer will be improved by inserting microchannels, for higher filling periods the electrowetting deteriorates the cooling. It can be concluded that the proposed system is promising, especially when frequencies in the range of a few Hz can be achieved.