具微奈米圖案化結構於光電材料應用與光學檢測性質之研究

Abstract

本論文採用時域有限差分(finite difference time domain, FDTD)之數值方法分析模擬週期性奈微米結構之光學特性。並且將奈微米週期性圖案化結構應用於光學膜面之塑膠基材表面以奈米壓印方式製作兩種不同形態之3D次波長結構，並檢驗其光學性質。於奈米光學模擬研究中發現，結構採尖錐或蛾眼圓錐形狀，當高寬比≧0.6時，在波長250nm~800nm範圍內其反射率均小於1%。實際之結構製作係於PMMA及PET等塑膠材料表面以熱壓印及紫外光固化成型結構。經過驗證實作結構之光學性質與FDTD數值模擬結果相當一致。 而另一項研究是提出一種創新的思維方法，開發出一種新型的”金屬嵌入式光罩製程技術”並應用於光電材料的藍寶石基板上製作光阻結構，再經由乾式蝕刻產生可應用於高亮度發光二極體 (light emitting diode, LED) 的圖案化藍寶石基板，此一新型光罩的特點是，除了具有一般模仁表面的凹、凸結構外，其微結構的部份表面 (例如結構凸起面、或結構凹下面) 會覆蓋一金屬層，可以阻擋 UV光的穿透。另外，此一光罩的材質為PDMS，為一可撓性甚佳的材質，可以遷就藍寶石基板的翹曲或不平整表面，達到全面緊密貼合的要求。利用PDMS軟模光罩成功於2吋藍寶石基板上製作線寬1 µm、週期2 µm 及光阻柱高度為1.4 µm 的六角最密堆積排列的結構。另外，透過LED基板磊晶與元件製作後，利用脈衝雷射蝕刻製作週期性微/奈米結構在發光二極體之透明導電層(transparent conducting oxide, TCO)表面，藉此破壞內部全反射以提升發光二極體之光萃取效率，實驗結果顯示可增進LED出光效率高達16%。

The development of coating technique to lower the reflected light and increase the optical efficiency of an optical system is a very important topic for modern optical elements. Recently, the use of anti-reflection (AR) structured surface has been proposed as an applicable alternative based on both the theoretical and the experimental study. In this article, antireflection structured surface was analyzed by the finite difference time domain (FDTD) method in the visible light spectrum and has been successfully fabricated on plastic substrate by nano-imprint process. The FDTD numerical calculation was used to analyze the AR structured surface by the designed profile 3-D pyramid and conical structure. Both of the structures showed the antireflection (AR) effect (reflectance<1%) when the aspect ratio of the 3D structure was larger than 0.8. In the nano-imprint process, hot embossing and UV curing process were applied to generate 3D nano-structure on plastic substrate as PMMA and PET. The optical property of the fabricated polymer film showed good agreement with the simulation result. In another work, we proposed a new type of metal embedded soft photo-mask based on a PMDS mold. Due to its compliance, this new soft photo-mask can from intimate contact with a slight-curved sapphire wafer and carry out UV exposure in photolithography and therefore forming PR microstructures on a sapphire substrate. During the exposure process, part of incident light is selectively blocked from metal film and others are guided by the convex PDMS structures and onto the photo-resist layer. For the soft PDMS photo-mask, hexagonal arrays of PR micro-pillars with a diameter around 1 µm and a height of 1.4 µm are successfully created on a 2 inch sapphire substrate. Subsequently, the pattern sapphire substrates (PSS) for LEDs can be readily obtained by applying ICP etching on this PR-patterned sapphire substrate. In addition, pulsed lasers were used to fabricate micro/nano structures on the transparent conducting oxide (TCO) layers of the light emitting diodes (LEDs) with pattern sapphire substrate to destroy the total internal reflectionat TCO/air and enhance the light extraction efficiency. It can improve LED light extraction efficiency up to 16%.