利用介電力於軟性薄膜製作微透鏡陣列

Abstract

本論文運用介電力製作軟性聚二甲基矽氧烷（PDMS）微透鏡陣列薄膜，並討論介電力與材料或電場分布的物理現象。微透鏡陣列在光學系統占重要位置且被廣泛的運用，並有相當數量的研究發表，微透鏡陣列經常應用於視覺顯示系統、光控制、光束成形等，例如於晶圓上模仿昆蟲複眼製作微透鏡陣列，搭配感光元件組合成微小化視覺系統；或將微透鏡陣列搭配振盪器與光纖組合成振盪掃描頭；亦或是利用微透鏡陣列聚焦紫外光顯影便為無光罩顯影製程。軟性微透鏡陣列擁有輕薄特性，在現今注重微小科技、可攜性的科技下，軟性微透鏡陣列可使光學系統微小化並且製作成可撓式科技產品增加可攜性。本論文利用具梯度的外加電壓驅動聚二甲基矽氧烷使之與表面張力平衡產生表面曲率不同的微液滴，製作成具焦距梯度的微透鏡陣列；於第二章對聚二甲基矽氧烷在平行電極內與聚乙烯（PE）基材的接觸角進行理論推導，利用平行板電極模型內有液態介電質，積分出於液滴的介電力，此推導可瞭解液滴於不同電壓下接觸角的變化。第三章介紹圓形平板電極設計並連結成電極陣列，各電極列利用分壓電路提供具梯度的電壓，可使液滴表面曲率呈梯度變化製作出具焦距梯度的微透鏡陣列。第四章陳述製作程序與實驗儀器及材料特性，流程為利用印刷電路板與銦錫氧化物（ITO）導電玻璃組合成平行電極，聚乙烯為基材，邊通電壓邊加熱讓聚二甲基矽氧烷固化成微透鏡陣列。第五章討論用指叉狀圓形電極所產生電場製作具焦距梯度的圓形透鏡陣列，利用聚乙烯與聚二甲基矽氧烷液滴製成軟性透鏡，並且與前章平行電極結果做討論比較。第六章開始講述橢圓透鏡製程，橢圓透鏡在廣角區域具有較圓形透鏡高解析度，也有廣泛的應用，可運用於視覺顯示也可用於雷射二極體光束整形，將橢圓光束輪廓經過聚焦成所需圓形光束。並介紹利用具有兩極的圓形電極的印刷電路板搭配銦錫氧化物導電玻璃組合成平行電極，並且亦是利用前章敘述之軟性聚合物材料，在液滴中產生區域性介電力使之輪廓轉變成橢球，固化後便成為軟性橢球微透鏡陣列。第七章為運用擁有四極的指叉狀圓形電極組的印刷電路板產生介電力製作成橢球，在聚二甲基矽氧烷液滴產生對角線方向的電場分佈，在與前述相同的軟性聚合物基材上，產生對角線排列的軟性橢球微透鏡陣列，可運用於可攜性視覺系統中，輔助系統增加視角，提高顯示品質。

ABSTRACT In this thesis, the fabrication of polydimethylsiloxane (PDMS) micro-lens array (MLA) on flexible polyethylene (PE) membrane and the physical characteristic research on dielectric force have been conducted. The MLA is important in optical system and has been widely used; considerable number of study has been published in visual and display systems, optical control, beam forming, etc. For example, MLS has been used to imitate insect compound eyes on the wafer combining with optical sensor to miniature visual system. It can be also implemented in a scanning head with oscillator and fiber. MLS can also be used to focus ultraviolet light in a maskless lithography process. Due to the thin flexible features and the current emphasis on portable micro-technology products, the soft MLA and miniaturized optical system could be integrated to increase portability. In this thesis, the use of dielectric force generated by applying gradient voltage drives PDMS to balance surface tension. In the second chapter, the theoretical derivation of the contact angle between PDMS within parallel electrodes and PE membrane coated with Teflon is discussed. The model of parallel-plate electrodes with liquid dielectric is used to calculate the external electric field and dielectric force. This derivation can facilitate the understanding of the contact angle of the droplet in different voltage changes. The third chapter describes the design of the circular plate electrodes on the printed circuit board used in the experiment. The electrode array using voltage divider provides a voltage gradient, thus the curvature of the droplets surface changes with the gradient. The forth chapter details the fabrication procedures, experiment apparatus and the properties of materials used in the experiment. The printed circuit board mentioned in the chapter 3 and a piece of indium tin oxide (ITO) conductive glass are combined to form parallel electrodes. They are then used in the experiment. PE serves as the substrate for MLA. Heating PDMS while applying voltage can be produced to flexible MLA thin-film. The chapter 5 discusses the application of interdigitally circular electrodes to generate the electric field, which is used to make the gradient of the focal length of circular MLA using the same PE substrate and PDMS droplets as in the previous chapter. And the results are discussed and compared with the micro-lens made based on circular plate electrode. The chapter 6 details the process to fabricate the elliptical micro-lens. Elliptical micro-lens has a wide range of applications for producing images of the high resolution at a wide viewing angle. For example, the ellipsoidal MLA can be applied in visual display as same as the circular MLA. It can also be used as the beam shaper of laser diode. In this case, the elliptical beam profile through the ellipsoidal MLA would be circular beam as required. The sixth chapter combines two-part electrodes on printed circuit board with a piece of ITO glass into a parallel electrode, which generates a local electric field to make the droplet ellipsoidal. The used material of the micro-lens is the same as the ones used in the former chapters to fabricate flexible ellipsoidal MLA. In the chapter 7, four-part rounded electrodes are utilized to produce ellipsoidal MLA. The diagonal distribution of the electric field and dielectric force in PDMS droplet results in the diagonal arrangement of the ellipsoidal MLA, where the polymer substrate is the same as aforementioned. This soft ellipsoidal MLA can be applied in portable vision systems to increase the viewing angle and to improve the display quality.