PDMS與金屬雙層結構微懸臂樑熱致動器設計與製備;Design and fabrication of PDMS/metal bimorph micro-cantilever thermal actuators

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题名:	PDMS與金屬雙層結構微懸臂樑熱致動器設計與製備;Design and fabrication of PDMS/metal bimorph micro-cantilever thermal actuators
作者:	林士傑;Lin, Shih-Jie
贡献者:	機械工程學系
关键词:	熱致動器;微製造;thermal actuator;micro-fabrication
日期:	2017-03-17
上传时间:	2017-05-05 17:42:39 (UTC+8)
出版者:	國立中央大學
摘要:	典型的熱致動器有同平面位移的冷熱臂與出平面位移的雙層結構懸臂樑，其中以雙層結構懸臂樑擁有大位移量、低操作電壓等優點，並根據不同的材料性質來增加其形變量，高分子材料因為擁有低楊氏模數與高拉伸率，近年來經常應用於雙層結構懸臂樑熱致動器。其中PDMS有低成本、光學穿透性、生物相容性等優點。微機電製程中傳統圖形定義的方式有乾蝕刻、模具轉印、舉離法，有別於上述方法，本文設計金屬微加熱器，藉由區域性加熱定義PDMS之圖形，此方法能少去光罩對準的步驟，達到自動對準的效果，在製程上減少光罩數量與製程步驟，並同時將PDMS與微加熱器作為雙層結構材料，製作雙層結構微懸臂樑之熱致動器，進而評估此類微致動器在製程上的可行性。本文製程首先設計金屬微加熱器與定義懸空區的區域，懸空區在此是以體微加工技術向基板蝕刻凹孔，取代傳統使用犧牲層的方式，減少微加熱器與接觸平面產生步階現象。接著利用微影蝕刻製作出微加熱器，並針對後續PDMS圖形定義所需之溫度控制，量測微加熱器的溫度特性。待PDMS圖形定義完成後利用濕蝕刻之方式釋放微懸臂樑結構。由形變量模擬分析金薄膜厚與形變量及彎曲角度關係設計本文的雙層結構微懸臂樑熱致動器。在PDMS圖形定義方面，是利用微加熱器區域性加熱來固化PDMS，因此PDMS的薄膜厚度會隨著加熱的溫度上升與時間增加而增加厚度，加熱溫度在120 ℃時，薄膜厚度呈現較小的變異性，當加熱溫度提升至150 ℃，薄膜厚度的變異性會大幅上升，造成變異性隨溫度提高而上升的原因推測是於高溫加熱時之溫度控制誤差，加熱時薄膜熱擴散使微加熱器周圍的PDMS薄膜不均勻所導致。 ;Typical micro-thermal actuators are based on the thermal expansion-induced displacement. To generate large displacement, one can use hot-and-cold-arm structures for the in-plane motion, and bimorph cantilever structures for the out-of-plane motion. The later usually has larger displacement, lower operation voltage, and wider design range. Recently, polymer materials are used in micro-devices, due to their low Young’s modulus and high elongation rate. In this study, polydimethylsiloxane (PDMS) is used as one of the bimorph material due to its compliance and biocompatibility. Polymer film patterning is usually conducted by dry etch, bond-detach lithography, or lift-off processes. We propose a novel technique that pattern the PDMS film directly on the metal cantilever by localized heating and eventually form a bimorph structure with the cantilever. This method not only reduces the number of the mask, hence reduce the process steps, but also achieves self-alignment. In the design, the metal micro-cantilever served as a heater is suspended above a cavity made by bulk-machining. This prevents the stepping problem at the anchor of the cantilever usually found in that made by surface micromachining. The micro heater properties are then characterized to precisely control the heating temperature when pattering PDMS. After the PDMS is patterned, we release the micro cantilever structure by wet etching and analyze the deformation and curved angle. The result shows that the thickness of cured PDMS film is a strong function of heating temperature and heating duration. When the heating temperature is at 120 ℃, it has less variability than at 150 ℃ and its variability will increased substantially with the temperature rising. Higher heating temperature and longer heating time result in thicker film, but the thickness variation between experiments also increases. This may be caused by the uncertainty of temperature control of micro-heater in high temperature.
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