Hot spots active-cooling micro-channel heat sink device, using electro-osmotic flow

Non-uniform heat flux generated by microchips causes “hot spots” in very small areas on the microchip surface. These hot spots are generated by the logic blocks in the microchip bay; however, memory blocks generate lower heat flux in contrast. The goal of this research is to design, fabricate, and test an active cooling, micro-channel heat sink device that can operate under atmospheric pressure while achieving a high-heat dissipation rate with a reduced chip-backside volume, particularly for spot cooling applications. An experimental setup was assembled and electro-osmotic flow (EOF) was used thus eliminating the high pressure pumping system. A flow rate of 82 μL/ min was achieved at 400 V of applied EOF voltage. An increase in the cooling fluid (buffer) temperature of 9.6 C, 29.9 C, 54.3 C, and 80.1 C was achieved for 0.4 W, 1.2 W, 2.1 W, and 4 W of heating powers, respectively. The substrate temperature at the middle of the microchannel was below 80.5 C for all input power values. Numerical calculations of temperatures and flow were conducted and the results were compared to experimental data. Nusselt number (Nu) for the 4 W case reached a maximum of 5.48 at the channel entrance and decreased to reach 4.56 for the rest of the channel. Nu number for EOF was about 10% higher when compared to the pressure-driven flow. It was found that using a shorter channel length and an EOF voltage in the range of 400 – 600 V allows application of a heat flux in the order of 10 W/m, applicable to spot cooling. For elevated voltages, the velocity due to EOF increased, leading to an increase in total heat transfer for a fixed duration of time; however, the joule heating was also elevated with increase in voltage.