水凝膠為具有三維網狀結構的親水性高分子聚合物，放置在水中能夠大量吸收水分澎潤而不溶解。以NIPAAm(N-isopropylacrylamide)為單體聚合而成的溫度感測型水凝膠，因具有低臨界溶解溫度(lower critical solution temperature)，當外在溫度的改變時會吸水澎潤或排水收縮產生劇烈體積變化，以及其接近室溫的操作環境，可應用於微機電系統裝置中。目前NIPAAm水凝膠的製程多為UV光聚合反應，此製程需添加光起始劑，但光起始劑價格昂貴、保存不易且毒性高，因此本文選用熱製程製備水凝膠薄膜並研究製程參數，選用的起始劑種類不具有光起始劑的缺點，熱固化製程具有微機電系統整合與應用的潛力。
本論文研究水凝膠的厚度及溫度對於收縮速度影響，並以表面張力沾附分析法與影像處理分析法，探討水凝膠在不同溫度的加熱固化情形，實驗將配置好的水凝膠溶液塗佈在矽晶圓上，於加熱過程觀察沾附現象同時記錄水凝膠白化過程，最後以微加熱器局部熱固化水凝膠薄膜並控制固化範圍。加熱排水實驗結果顯示，相同厚度的情況，溫度越高水凝膠收縮速度越快；而相同溫度的情況下，厚度越薄水凝膠收縮速度越快。加熱固化製程實驗結果顯示，當加熱固化溫度越高水凝膠的固化速度越快，以阿瑞尼斯方程式計算出活化能約47 kJ/mol，相較於表面張力沾附分析法，影像處理分析法能較完整呈現固化過程。最後以微加熱器搭配電致冷晶片作試片溫度控制，展示局部熱固化水凝膠薄膜器控制固化範圍的可行性。

Hydrogel is a hydrophilic three-dimension network polymer, which can swell and contain large amount of water within its structure without dissolution. N-isopropyl-acrylamide(NIPAAm) hydrogel has lower critical solution temperature near room temperature. It swells or shrinks below or above the temperature. The dramatic volume change and the low operating temperature characteristics make it a promising mechanism in MEMS devices. To pattern the NIPAAm films, UV photopolymerization is the most common method, which requires the addition of photoinitiators. However, the photo initiators are expensive, difficult to store, and have highly toxic. In this study, we propose a thermal process to prepare and pattern hydrogel thin films, which do not have the disadvantages of the photoinitiator. The thermal process also has the potential fabrication integration in MEMS thermal actuators.
In this thesis, we explore the shrinkage rate, the thermal curing processes, and the local curing of NIPAAm films. In the experiments, the hydrogel solution is coating on a silicon wafer. The wettability tests and optical inspections are used to observe the adhesion phenomenon and the color changes during the heating process at different temperatures. Finally, the micro-heater is used to locally cure the hydrogel film at different environment temperatures to controls the size of the films.
The results show that with the same thickness, the higher the temperature, the faster the hydrogel shrinks; while at the same temperature, the thinner the thickness, the faster the hydrogel shrinks. In the heating process experiments show that the higher the heat temperature is, the faster the hydrogel polymerizes. The activation energy calculated by Arrhenius equation is around 47 kJ/mol. Compared with the wettability tests, optical inspection method can show the curing process with less errors. Finally, the micro-heater experiments demonstrate the feasibility of controlling the curing range of the hydrogel film with a local curing and temperature control of the substrate.

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