| Summary: | 博士 === 國立交通大學 === 機械工程系所 === 94 === In this study, we employ a low-temperature stress-free electroplated nickel (EL) process with the addition of uniformly dispersed nanoparticles of diamond, CNTs or SiO2 to investigate “nanocomposite effects” for the first time on the modification of the mechanical properties inclusion thermal expansion coefficient (CTE), of nickel and its correlation to power and reliability improvement of electro-thermal microactuators. By measuring the resonant frequency, the E/ρ ratio of the cantilever beam with Ni-damond nanocomposite reaches 1.3 times of the pure nickel one and the similar enhancement of the Ni-CNTs nanocomposite is about 1.47 times. In addition, the nano-indentation measurement shows that the Young’s modulus and hardness of the Ni-diamond nanocomposite film electroplated in the bath with 2g/L diamond can greatly increase up to 230GPa and 11.9GPa, respectively. The Ni-CNTs nanocomposite film electroplated in the bath with 0.028g/L CNTs can greatly increase up to 235GPa and 7.9GPa, respectively. The CTE of the cantilever beam with Ni-damond nanocomposite reaches 2 times of the pure nickel one and the similar enhancement of the Ni-CNTs nanocomposite is about 1.48 times.
For the electrical property, the resisitivies of these two composites, 126.56×10-9Ω-m for Ni-diamond and 156.78×10-9Ω-m for Ni-CNTs, respectively, indicate both films have better electrical conductivity than the doped polysilicon (~10×10-6Ω-m). Based on the 4-point probe measurement, it is found that the intrinsic bulk resistivities of the nanocomposite thin films can be characterized using Maxwell-Wagner model for a two phase mixture. Therefore, with the enhancements both on the mechanical and physical properties, the novel nanocomposites show the potential applications on the MEMS, especially for high-frequency resonant device fabrication.
An electro-thermal microactuator is designed and fabricated using the novel nanocomposites. Device characterization reveals dramatic performance improvements in the electrothermal microactuator that is made of the nanocomposite, including a reduction in the input power requirement and enhancement on operation reliability. In comparison with the microactuator made of pure nickel, the nanocomposite one can save about 73% the power for a 3μm output displacement and have a longer reversible displacement range, which is prolonged from 1.8μm to more than 3μm. Measurement results show that the microactuator plated with CNTs 0.028g/L needs the power requirement less 95% than the pure nickel device at the same output displacement of 3μm. The performance improvement of the electrothermal microactuator made of the nanocomposite, including device strength and power efficiency, has shown to be similar to the Ni-diamond nanocomposites.
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