電鍍鎳基奈米鑽石與奈米碳管複合材料於微機械式共振器之應用

Abstract

在無線通訊與消費電子系統的應用上，石英共振器為重要的時間或頻率的參考源，但石英共振器在製程上難與其他電路做直接性的整合。相較之下，微機械式共振器展現高度的製程整合性，使其逐漸取代石英共振器之應用。本論文首先提出以電鍍鎳基奈米鑽石粒子與奈米碳管兩種奈米複合材料，製作微機械式共振器。為了完全利用奈米粒子(奈米鑽石粒子與奈米碳管)的特性，奈米粒子必須在電鍍液中均勻分散。目前所使用的奈米鑽石粒子能均勻分散於電鍍液中，而奈米碳管則呈現聚集狀態，需進行分散處理。在此採用硫酸/過氧化氫與十二烷基硫酸鈉水溶液兩種配方做為奈米碳管的分散處理液。由實驗結果可知，十二烷基硫酸鈉水溶液所處理的奈米碳管在分散狀態與鍍層中的含量皆優於硫酸/過氧化氫處理，用於微機械式共振器的製作上，可得到較高的共振頻率提升。製程上，鎳基奈米複合材料所製作之懸浮微結構常因為殘留應力導致翹曲。此翹曲問題在此可藉由降低電鍍之電流密度而減緩。當電流密度為0.8 mA/cm2時，可得到低應力梯度之純鎳、鎳-奈米鑽石、鎳-奈米碳管，值各為-3.23、-5.65、-4.75 MPa/μm。相較於15.3 mA/cm2電流密度，可降低41~21%的應力梯度。由於奈米鑽石粒子(2 g/L)與奈米碳管(1 g/L)的添加，所得到的鎳基奈米複合材料各有1.39與1.46倍的楊氏係數/密度比值，高楊氏係數/密度比值有助於提升共振器的共振頻率。在此採用梳狀與橋狀微機械式共振器的結構設計。對於梳狀設計，鎳-奈米鑽石(2 g/L)與鎳-奈米碳管(0.028 g/L)相對於純鎳，各提升14% 與 8%的共振頻率；橋狀設計，共振頻率的提升量為45% (2 g/L) 與 27% (1 g/L)。在共振頻率提升的同時，共振器的品質因子並不會因為奈米粒子的添加而大幅衰減。

Quartz plays an important role for time and frequency reference in wireless and consumer electronic systems. Unfortunately, quartz resonator is not easy to integrate with other electronics directly. Currently, micromechanical resonator has become an alternative device to replace quartz resonator for better integration. Based on the technology trend, this dissertation explores the feasibility of electroplated Ni-diamond and Ni-CNT (Ni-Carbon Nanotube) nanocomposites for micromechanical resonator applications and proposes a proper fabrication process where good particle dispersion characteristics including nano diamonds and CNTs in electrolyte can be obtained to fully adopt the physical properties of the nano materials for achieving composite effects. The nano diamond and CNT particles can exhibit good dispersion using ultrasonication and the surface treatment of H2SO4/H2O2 and SDS water solution, respectively, that result in better frequency enhancement in nanocomposite micromechanical resonators. Meanwhile, as-plated Ni-based nanocomposite film is usually accompanied with residual stress that would cause significant undesired structural deformation. The stress issue can be evidently reduced by lowering plating current density. For the films plated with the density reduction from 15.3 mA/cm2 to 0.8 mA/cm2, about 41%~21% stress gradient reduction can be realized. Experimental results show that the stress gradients are -3.23, -5.65, and -4.75 MPa/μm for Ni, Ni-diamond, and Ni-CNT plate with 0.8 mA/cm2, respectively. The stress gradients are low enough to achieve a fully suspended micromechanical structure without any noticeable deformation. In addition, 39% and 46% of E/ρ enhancements can be achieved by the nano diamond (2 g/L) and CNTs (1 g/L) incorporations, respectively. The higher the E/ρ ratio is, the higher resonant frequency performance will be in the micromechanical resonators. Thus, in the work, comb and CC-beam designs are adopted for the validation of the performance improvement of the micromechanical resonators made of the nanocomposites. Measurement results show 14% and 8% and 45% and 27% of frequency enhancements can be obtained in both of the comb resonators made of the Ni-diamond (2 g/L) and Ni-CNT (0.028 g/L) and the CC-beam resonators made of nano diamond (2 g/L) and CNTs (1 g/L), respectively. The results also indicate no Q degradation happens in these nanocomposite resonators.