電化學鎳基奈米複材特性探討與在微機電系統的應用

Abstract

本研究利用添加奈米粒子製作之鎳基奈米複合材料，由於是由兩種或兩種以上性質不同的物質組合而成，常可以彌補單一材料的缺點，產生原來材料所不具備的新特性，目前已成功將奈米鑽石粒子、奈米碳管與二氧化矽加入鎳電鍍液中製作鎳基奈米複合材料的低溫製程(50℃)，且應用在微機電元件中。 藉由量測藉由量測懸臂樑的共振頻率，可以得到鎳鑽石奈米複合材料的揚氏係數對密度的比值高達純鎳的1.3倍，鎳基奈米碳管複合材料是純鎳的1.47倍。除此之外，奈米壓痕的量測結果指出，在每公升鍍液裡有2克的鑽石粒子（平均粒徑500nm）溶液中鍍出來的鎳基鑽石奈米複合材料薄膜的揚氏係數及硬度值分別提升為230GPa及11.9GPa，其楊氏係數值與硬度值分別大約是純鎳薄膜的1.2倍與2.63倍，另一方面，鍍液中添加每公升0.0028克的奈米碳管，則鎳基奈米碳管複合材料薄膜的楊氏係數值與鎳基鑽石奈米複合材料近似，但硬度值卻是變小的。另外，在熱膨脹係數方面，鎳鑽石奈米複合材料與鎳基奈米碳管複合材料分別為50×10-6/℃與34.8×10-6/℃，其熱膨脹係數分別大約是純鎳薄膜的2倍與1.48倍。 在電性方面，這兩種材料的電阻率都顯示出比掺雜的複晶矽(~10×10-6Ω-m)還要好的導電性，鎳基鑽石奈米複合材料與鎳基奈米碳管複合材料分別是126.56×10-9Ω-m與156.78×10-9Ω-m。以四點探針的量測為基礎，者兩種奈米複合材料的電阻率可以由Maxwell-Wagner的兩項混合物模型來描述其特性。所以，由這些機械及物理性質上的優異增強，高頻共振元件的製程應有幫助。 此外，我們以電熱式微致動器作為在此鎳基奈米複合材料的載具，在鎳基奈米複合材料所製作之電熱式微致動器性能量測，在相同的位移量時，鎳基鑽石奈米複合材料與鎳基奈米碳管複合材料製作之電熱式微致動器，所需所需輸入功率比純鎳的微致動器分別減少73%與95%，且擁有更大的操作位移。

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.