矽膠材料於微光學上的應用

Abstract

聚二甲基矽氧烷 (PDMS)有許多優異的特性並已經應用在很多不同領域，例如微機電、生醫和化學溶膠改質。本論文主要是應用矽膠高分子PDMS 的特性去製作三種微光學元件：(1)折射式微透鏡；(2)反射式微透鏡；和(3)繞射光柵和相關元件。 在折射式微透鏡製作中,主要是利用準分子雷射在聚碳酸酯（PC）薄板上作圖案，接著利用旋轉塗佈機將聚甲基丙烯酸甲酯（PMMA）液體塗佈在圖案上，藉由薄膜重力形成微曲面，利用這曲面是當成微型透鏡模具,接著將PDMS 液體倒入模具中，固化後形成微透鏡。藉由PDMS 易脫膜的特性，PDMS 微透鏡可以輕易脫離聚甲基丙烯酸甲酯（PMMA）模具。而微透鏡的曲率和焦距可以藉由微孔的大小跟PMMA 的膜厚來控制。 在反射式微透鏡製作中，主要是承接折射式微透鏡製作和PDMS 的高反射率材料的研發。藉由光散射理論，PDMS 高分子混合奈米尺寸的二氧化鈦粉末形成高反射率材料，接著倒入PMMA 模具，形成凸型的微透鏡。藉由PDMS 二次翻模，可以分別製作出反射式PDMS 凹、凸微透鏡。 在繞射光柵製作中，主要是基於金屬覆蓋於PDMS 表面，這表面會自發展週期1-2微米波形結構的原理。在這裡，我們利用強酸使PDMS 表面形成氧化層，進而導致波紋結構產生，藉由控制PDMS 的彈性模數、強酸的比例和浸泡的時間，波紋的週期可以被控制。藉由外部拉力的引導，表面的波紋結構可以被整齊的排列以形成繞射光柵。

The silicone rubbery material, polydimethylsiloxane (PDMS), has attracted the attention of many material scientists recently as there are potential applications ranging from microelectromechanical systems (MEMS) to biology, due to its excellent physical and chemical characteristics. This thesis focused on the fabrication of microoptical elements by the use of PDMS polymer, included refractive microlenses, reflective microlenses and diffractive gratings. For the fabrication of refractive microlenses, concave microlens molds were fabricated through spin-coating processes suspended liquid PMMA films on the micro-drilled holes, leading to the formation of the special curvature due to the weight of PMMA films. Then, liquid PDMS polymer was cast onto the PMMA concave molds. After curing PDMS polymer, the solidified PDMS microlens arrays could be easily stripped from the PMMA film due to the hydrophobic nature of PDMS polymer. With the change of diameters of microholes and thicknesses of PMMA films, the suspended height of films was surely controllable. Therefore, the curvature radiuses and shapes of microlens also depended on the diameters of microholes and the thicknesses of PMMA films. For the fabrication of reflective microlenses, we connected the fabrication of refractive microlens and the preparation of high-reflectance material. Based on light scattering theory, PDMS rubber polymers mixed with nanoscale TiO2 powders to form directly high-reflectance materials. Finally, both of concave and convex elements could be fabricated through soft replica molding processes and these elements could directly reflect light without the deposition of metal coatings. Wrinkles with the periodicity of 1-2 micrometer would be spontaneously developed on PDMS surface covered with a layer of gold films. Based on this phenomenon, a novel way to fabricate diffractive gratings could be proposed. The surface layer of PDMS was immediately oxidized, after it contacted with the acid solutions (H2SO4/ HNO3). A bilayer system, a stiff layer (an oxidized PDMS film) was capped on the soft foundation (a PDMS film), would lead to the formation of wrinkles. By the control of elastic modulus of PDMS, the mixed ratio of strong acid solutions and the dipped duration, the periodicity of wrinkles could be adjusted. Wrinkles, which could be arranged orderedly through the guidance of external forces, were regarded as optical gratings.