多元尺度奈微米大面積壓印技術於顯示器之應用 --- 子計畫二：以奈米壓印設計製作具光子晶體之高效能暨高指向性的發光二極體

Abstract

本計畫內容是使用奈米壓印的方法來達到製作具光子晶體之高效能暨高指向性的發光二極 體。此計畫所設計發展之高效能暨高指向性的發光二極體，將搭配子計畫一所發展之奈米偏極光 學元件，發展出具高效能之顯示器背光模組。 光子晶體(光子能隙結構晶體)的概念於1987 年首先由Yablonovitch 及John 分別被提出之 後，隨著實驗技術進步與精密儀器不斷提升，以及各種製作相關結構的製程技術發展不斷進步， 光子晶體的實驗成果也更趨完整，光子晶體才受到注目。在光子晶體這種週期性的結構中，基本 上是在二維或三維空間中，讓材料折射率(或介電常數)產生週期性變化的結構，這種結構模仿原 子在固態晶體中的排列。所以，類似電子於固態晶體中的能帶結構，在光子晶體中就產生光子的 能帶結構。在這一項計畫中提升發光效率機制有二：一為利用表面週期性結構造成布拉格散射， 以減少全內反射情形發生；第二個則是利用光子晶體能隙將傳導模態導引出來，以提升外部量子 效率。在另一方面，光子晶體因其周期結構對光子在傳波狀態（guiding mode）方向產生禁制能 帶，抑制傳波狀態而使光傾向自正向發出，進而達到了光的高指向性的目的。本計畫之第一年將 設計LED 磊晶層及光子晶體之結構材料與尺寸，並使用FDTD 進行光學模擬，以提高光效率與高 指向性。 本計畫之第二年將製作原型LED 磊晶層外，並與子計畫二、三合作設計開發奈米壓印之模具 與技術以實現期望之光子晶體。主軸為利用各式各樣之元件表面圖案的壓印來提高出光效率 (light extraction)以及利用光子晶體的特性提高光指向性(directionality)，對發光二極體而 言，如應用在照明用途或顯示器光源上，奈米壓印法(nanoimprinting lithography)是極具潛力 的選擇。近年來微奈米製造技術蓬勃發展下，各種創新製造技術如半導體表面加工製程、LIGA 製 程、奈米壓印在各個領域不斷提出。奈米壓印技術於1995 年由美國普林斯頓大學電機系Stephen Y.Chou 教授所提出，此技術具有成本低、製程簡單、產量高的優勢。最重要的是，利用奈米壓印 可以不受到光源波長的限制，可以製作出解析度小於100nm 以下的特徵圖案，是一種極具潛力的 半導體製程技術。此外，對傳統的光學微影技術而言，即使是輕微的曲面，也會因為景深的限制， 而無法有效的去進行圖案的轉移。對壓印技術而言，因為是採用接觸的方式進行圖案化的動作， 因此對於非平整表面的圖案轉移步驟，將是較佳的選擇。壓印技術的第一步就是模具的製作，由 模具來定義特徵圖案。本子計畫嘗試搭配使用子計畫三製作出微奈米級的鑽石基模具；並分析製 程參數對模具深度的均勻性影響。並針對高溫壓印製程，進行製程參數測定與圖案轉移性優劣性 質做探討，以達到好的光子晶體效果。本計畫之第三年將利用田口法及基因演算法來增加發光二 極體的效率與高指向性，並增加製程良率。

This proposal is planned to use the method of nano-imprinting to fabricate photonic crystals on the top surface of the LED, in order to render high efficiency and directionality. The developed LEDs with high efficiency and directionality will be utilized as the light sources in the backlight unit (BLU) with the nano-imprinted wire grid polarizer (WGP), leading to a high-efficiency BLU. The concept of photonic crystals was first introduced in 1987 by Yablonovitch and John. With significant progress in fabrication technology and precision machine later, the technology for fabricating varied structures of a LED become more complete with associated experimetnal validation. The photonic crystals then draw much attention. In the 2D or 3D periodic structures of a typical photonic crystals, the material refraction indices become varied in periodic fashion. This variation mimic atomic alignment in solid crystals. Therefore, it is similar to band gaps for the electrons in solid crystals. In results, the photonic crstals generate the effects of band gaps for photons. There are two mechanisms proposed in the porposal to increase the emission efficiency: (1) induce Bragg diffraction by the periodic structure of photonic crystals in order to mitigate internal reflections; (2) using the photonic crystals to induce guiding mode in order to increase external quantum efficiency. On the other hand, due to the band gap effects along the giuding mode caused by the periodic structres and photonic crystals, the high directinality of the LED can be achieved. In the first year of the project execution, the LED epitaxy and the dimensions, materials and structures of Photonic crystals will be designed. The method finite difference time domain is then used to simulate the optics, in order to raise light efficiency and directionality. In the second year of project execution, a process of nano-imprinting will be developed to realize the photonic crystals on LEDs. The method of nano-imprinting was first introduced by Prof. Stephen Chou with merits of low cost, simpleness and high productivity. Most importantly, the nano-imprinting is not limited by the wavelength of light source and then capable of fabricating pattern with resolution less than 100nm. This nano-imprinting is then a potentially high-value semi-conductor processing technology. For photo-lithography, even a lightly-curved profile is difficult ot fabricate due to the limitation of focusing depth. To nano-imprinting, however, the patterning by the contact-imprinting technology is s better solution. The first step of nano-imprinting is the manufacturing of a mold to realize the pattern. This proposal will use the diamond mold fabricated by the sub-project 3, and then anlayze the process parameters for fabrication quality for achieving optimum photonic crystals. In the third year of the project execution, the Taguchi anf Genetic Algorithm will be used to optimize the efficiency, directionality and yield rate.