Fabrication and characterization of MEMS thermal interface materials

This work presents the fabrication and characterization of MEMS thermal interface materials. Different materials were used to fabricate and characterize different configurations of sample thermal interface materials. The materials used as thermal interface materials are vertically aligned carbon nanotubes (VACNT), mercury and glycerin.;VACNT turfs were fabricated on 4 x 4 mm2 silicon substrates using a chemical vapor deposition process (CVD). The process of thermocompression bonding of VACNT to metallized substrates was used to fabricate a low-resistance thermal interface material. The resulting structures consisted of a VACNT turf sandwiched between two metallized silicon substrates. Both full coverage turfs and patterned turfs were tested. In addition to the initial as grown and the final bonded structures, intermediate structures resulting from the steps of the thermocompression bonding process were tested. A total of seven configuration of VACNT turfs were tested. A thermal interface resistance as low as 4.36 mm2K/W was measured for the patterned turf, while it was 108.2 mm2K/W for the full coverage turf. Mercury micro droplet arrays of two sizes were fabricated and characterized.;Mercury arrays were fabricated by preferentially condensing mercury vapor on micromachined gold targets. The arrays included a 40 x 40 array (1600 grid) and two 20 x 20 arrays (400 grid). Similar to the VACNT turfs, the mercury arrays were assembled on 4 x 4 mm2 silicon substrate. A thermal interface resistance as low as 0.253 mm2K/W was measured for the mercury arrays. A model to predict the thermal resistance of liquid-metal micro droplet arrays was presented and compared to the experimental results. Based on the experimental results and modeled data, an average contact resistance between the mercury arrays and silicon substrates of 0.14 mm2K/W was estimated.;Glycerin droplets, 1 muL, were also tested as thermal interface materials. Copper nanoparticles having a diameter of 25 nm were dispersed in glycerin at different volume fractions to enhance its thermal conductivity. An increase of 57.5% in the thermal conductivity of glycerin was measured at a volume fraction of 15%. A minimum thermal interface resistance of 30.37 mm 2K/W was measured for the glycerin micro droplets. The effect of nanoparticles size on the effective thermal conductivity of glycerin was studied. Nanoparticles with diameters of 60-80 nm and 300 nm were dispersed in glycerin at a volume fraction of 5%, and their results were compared to those of the 25 nm particles. The thermal interface resistance of glycerin micro droplet arrays was then predicted for different volume fractions of copper nanoparticles.