電鍍鎳-鑽奈米複合材料之熱膨脹係數及疲勞特性研究

Abstract

電鍍鎳是微機電系統裝置中，常見的結構材料。近來更因為奈米科技的發展，結合奈米顆粒形成複合材料，不但強化了原先材料的特性，也增廣了電鍍鎳的應用範圍。在本論文中，將針對電鍍鎳-鑽奈米複合材料，於其熱膨脹係數變化機制、材料應用、材料可靠度議題等方面，做一完整的探討與研究。 於熱膨脹係數變化機制方面：利用文獻和X光繞射實驗的相互比對下，電鍍鎳基奈米複合材料內的殘留應力類型，可以藉由X光繞射角之峰值變化定義之，且被認定為最有可能影響奈米複合材料之熱膨脹係數變化的因素。而且此一來自製程的殘留應力，其類型可以由鎳基材與添加顆粒間的硬度差異或楊氏係數差異驗證之。根據實驗量測結果，電鍍鎳基材結合奈米鑽石顆粒，所形成的奈米複合材料呈現殘留壓應力，其熱膨脹係數可由原先電鍍鎳的23 ×10-6/℃提升至50.1 ×10-6/℃；相對地，當電鍍鎳基材結合奈米二氧化矽顆粒，所形成的奈米複合材料則呈現殘留張應力，其熱膨脹係數由原先電鍍鎳的23 ×10-6/℃減少至18 ×10-6/℃。 於材料應用方面：利用雙層板效應，電鍍鎳-鑽奈米複合材料的熱膨脹係數特性已被應用於一新型的鎳基熱雙層結構上。當熱雙層結構由電鍍鎳和電鍍鎳-鑽奈米複合材料疊合而成時，藉由電鍍鎳和電鍍鎳-鑽奈米複合材料兩者電鍍順序的調換，即可簡單地製作出向上或向下致動的熱雙層結構。加上這兩層鎳基材料具有相似的晶格結構的和相同的電鍍沈積溫度，其所製成的熱雙層結構，由實驗測試結果可知，擁有較佳的界面結合力和較低的熱殘留熱應力。 於材料可靠度議題方面：利用微機電製程與電鍍技術，分別製作電鍍鎳和電鍍鎳-鑽奈米複合材料的微懸臂樑測試試片，藉由出平面彎曲測試的方法，討論電鍍鎳與電鍍鎳-鑽奈米複合材料的疲勞特性與楊氏係數特性。根據實驗量測結果得知，由於奈米顆粒的添加，使得材料的延性降低，造成複合材料的疲勞強度略低於鎳基材；然而，當所添加的奈米顆粒尺寸由350 nm降至50 nm時，顆粒的尺寸效應則可使電鍍鎳-鑽奈米複合材料有~13.6%的楊氏係數提升，且具有與電鍍鎳可相比較的疲勞強度(~2.4 GPa)。

Electroplated Ni is the common structure material in MEMS devices. Recently, the nanotechnology has advanced it for enhanced material properties and wide applications by incorporated nano-particles. In this dissertation, the electroplated Ni-diamond nanocomposite has been investigated thoroughly in terms of CTE variation mechanism, material application, and reliability issue. For the CTE variation mechanism, through the XRD investigation, residual stress types of Ni-based nanocomposites can be determined. These residual stresses resulted from co-deposited process are thought as the promising factor to affect the CTE variations. According to measurement results, the incorporated nano-diamond particles in Ni matrix will enhance the CTE of electroplated Ni from 23 to 50.1 ×10-6/℃ with residual compressive stress; oppositely, the incorporated nano-SiO2 particles in Ni matrix will diminish the CTE of electroplated Ni from 23 to 18 ×10-6/℃ with residual tensile stress. For the material application, the CTE property of Ni-diamond nanocomposite is applied on a newly Ni-based thermal bimaterial structure by bimorph effect. Thermal bimaterial structure made of electroplated Ni/Ni-diamond nanocomposite can achieve upward and downward out-of-plane displacement easily by controlling the plating sequence of electroplated Ni and Ni-diamond nanocomposite. Since Ni and Ni-diamond nanocomposite have different CTE but similar crystal structure and process temperature, the fabricated thermal bimaterial structures show better interfacial bonding strength and smaller residual thermal stress. For the reliability issue, the characterizations of fatigue and Young’s modulus have been studied employing the bending-test method on the specimens made of electroplated Ni and Ni-diamond nanocomposites. According to the measurement results, Ni-diamond nanocomposite has slightly smaller fatigue strength than that of pure electroplated Ni due to the ductility reduction resulted by the nanoparticles. However, once the particle size of nano-diamond is reduced from 350 to 50 nm, it has been found that the electroplated Ni-diamond nanocomposite can have higher Young’s modulus (~13.6% enhancement) and comparable fatigue strength (~2.4 GPa) with that of pure electroplated Ni.