鎳-磷-碳管及鎳-磷-鑽石奈米複合材料薄膜的性質增強及其在微機電元件上的應用

Abstract

在現今的微機電元件製程中，由於複晶矽的優良機、電性質，所以一直是最普遍被應用的材料。然而高掺雜複晶矽沉積的高製程溫度使得複晶矽本身不適合於互補式金屬氧化物半導體的整合。為了製造一個完全整合的微機電元件，找出一個擁有跟複晶矽類似的材料性質的替代性物質是必須的。所以本篇論文即是針對實現此一目標而建立。在實驗中，一個鎳-磷-奈米碳管(無電極電鍍鎳-磷-奈米碳管)及鎳-磷-鑽石粉末(無電極電鍍鎳-磷-鑽石粉)奈米複合材料薄膜的低溫合成與相關製程已經成功的被發展並應用於微機電上。奈米壓痕的量測結果指出，在每公升鍍液裡有0.028克的奈米碳管溶液中鍍出來的鎳-磷-碳管複合材料薄膜的揚氏係數及硬度值分別大大的提升至665.9GPa及28.9GPa，這值大約是純鎳-磷薄膜的4倍大。另一方面發現到，由於掺雜奈米鑽石粉末，鎳-磷-鑽石奈米複合材料薄膜的揚氏係數及硬度值卻是變小的。除此之外，藉由量測懸臂樑的共振頻率可以得到鎳-磷-碳管奈米複合材料的揚氏係數對密度的比值高達純鎳的3.9倍，鎳-磷-鑽石奈米複合材料是純鎳的3倍。在電性上來講，這兩種材料的電阻率都顯示出比掺雜的複晶矽(~10x10-6Ω-m)還要好的導電性，鎳-磷-奈米碳管與鎳-磷-鑽石粉分別是1.903x10-6Ω-m與1.399x10-6 Ω-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馬克斯威爾-華格納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，這兩種新的奈米複合材料可以被應用於微機電上，特別是高頻共振元件的製作。 除此之外，我們也用這兩種新的奈米複合材料設計並製作出了一種電熱式的微致動器。在這元件的量測上，鎳-磷-碳管製成的微致動器的最大伸長位移量可以到達純鎳製成的微致動器的4倍之多。在相同的位移量時，所需的輸入功率又比純鎳的致動器小很多。相同的特性增強在鎳-磷-鑽石奈米複合材料微致動器中也被發現。這最大的伸長量也是純鎳的4倍。這種由這新的奈米複合材料所製成的電熱式微致動器的性能上的改良，包括元件的機械強度和能量效益，被證實和我們先前用直流電鍍法製作的鎳-鑽石複合材料微致動器相似，但是甚至比直流電鍍製成的鎳-鑽石複合材料元件擁有更好的機械強度和能量效益。

In the contemporary fabrication process of MEMS devices, polysilicon is the working horse material due to its excellent mechanical and electrical properties. Nevertheless, the high processing temperature (>1000□C) for highly-doped polysilicon deposition makes itself not suitable for CMOS integration. In order to fabricate a fully integrated MEMS device, it is necessary to find an alternative material while keeping the similar material property to that of polysilicon and this thesis is aimed to achieve such a goal. In this work, a low temperature synthesis (~80□C) and related fabrication processes of the Ni-P-CNTs (electroless phosphorus nickel-carbon nanotubes) and Ni-P-Diamond (electroless phosphorus diamond) nanocomposites have been successfully developed and characterized for MEMS applications. The nano-indentation measurement shows that the Young’s modulus and hardness of the Ni-P-CNTs nanocomposite film electroplated in the bath with 0.028g/L CNTs can greatly increase up to 665.9GPa and 28.9GPa, respectively, which is about four times larger than that of pure nickel. On the other hand, it is found that the modulus and hardness of the Ni-P-Diamond nanocomposite films decrease with the incorporation of the nano-diamond powders. In addition, by measuring the resonant frequency, the E/ρ ratio of the cantilever beam with Ni-P-CNTs nanocomposite reaches 3.9 times of the pure nickel one and the similar enhancement of the Ni-P-Diamond nanocomposite is about 3 times. For the electrical property, the resisitivies of these two composites, 1.903x10-6Ω-m for Ni-P-CNTs and 1.399x10-6Ω-m for Ni-P-diamond, respectively, indicate both films have better electrical conductivity than the doped polysilicon (~10x10-6Ω-m). Based on the 4-point probe measurement, we 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. The actuator made of Ni-P-CNTs can provide four times maximum elongation larger than that made of pure nickel. With the same displacement, the input power is much less than that of pure Ni. Similar enhancement is also found in the actuator made of Ni-P-diamond nanocomposite. The maximum elongation is also four times larger than the pure one. The performance improvement of the electro-thermal microactuator made of the nanocomposites, including device strength and power efficient, have been proved similar to the actuator made of the electroplated Ni-Diamond nanocomposite [1], even with more power efficiency and higher strength than the electrolytic Ni-Diamond device.