本場演講者鄭克勇教授

A Novel Boundary-Confined Method for High Numerical Aperture Microlens Arrays Fabrication

Professor Guo-Dung John Su

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所 蘇國棟教授

We present a technique to improve microlens arrays (MLAs) uniformity after the thermal reflow process. Microlens arrays (MLAs) usually form a layered structure in application-specific optical systems, such as backlight modules for liquid crystal displays (LCD), extraction improvement film for layered light emitting devices, wavefront sensors, image recorders, and a focusing component in the optical communication devices. It is hard to make small lenses and large arrays by traditional machining. Although several methods are proposed to replace the traditional machining, thermal reflow process is widely used to fabricate MLAs.

To overcome this difficulty, a novel method is proposed and demonstrated in this paper. It is called the boundary-confined method. A boundary between each PR cylinder is defined first by a thin negative tone PR. A thermal reflowing of a 2^nd thick PR is halted at the boundary, as shown in Fig. 1. The uniformity can be improved without the cling phenomenon. Besides, the boundary is narrow and only a small amount of fill-factor is sacrificed. The height of the microlens is adjustable by the different diameter of PR cylinders inside the same boundary wall. We achieved high uniformity and high-NA (numerical aperture) simultaneously without sacrificing fill-factor too much. In order to improve fill-factor, residual PR (photoresist) between the photoresist cylinders are used to make photoresist flow outward in standard thermal reflow processes. PR cylinders, however, merge together easily due to an inexact reflow time and temperature distribution. This results in low uniformity and small lens height or low-NA. We proposed a boundary-confined method to pattern thin PR holes to prevent PR microlenses from merging together even after a long reflow time. Thick PR cylinders are patterned inside thin PR holes served as boundaries. PR microlenses are formed after reflowing the thick photoresist cylinders. Both the uniformity and the height of microlens can be well controlled. Besides, the fill-factor is high due to the high resolution at thin photoresist layer in photolithography. Our results show that the microlens is approximately a hemispherical profile. The gap between microlenses with 48 mm diameter in hexagonal arrangement is 2 mm and the height of microlens is 22 mm, as shown in Fig. 2. This work is also patterned under US 7,713,453 B2.

利用高解析度同步輻射光源之光電子發射能譜，本論文將有系統地研究寡聚芴化物(oligofluorenes)(圖一)之電子結構、界面化學以及變溫特性。首先，我們觀察並歸納出寡聚芴化物的能階結構和許多重要的特性，包括游離能、界面電偶極和發光能隙，同時我們也在這一系列寡聚芴化物中發現到一些規則性的趨勢。而根據本篇論文的研究，寡聚芴化物的支鏈取代物將會大幅地影響到其電子和光學特性，寡聚芴化物之元件操作性能，也會受到支鏈取代物的影響。為了讓寡聚芴化物元件之電子注入能障降低，並且提升電子在陰極界面的注入效率，氟化鋰和氟化銫等鹼金屬氟化物將被用作為寡聚芴化物之n型摻雜物，這兩樣n型摻雜物都能夠與寡聚芴化物反應並造成n型摻雜的結果，但卻不需要鋁的存在，這使得寡聚芴化物元件在陰極金屬的使用上有了更多的選擇(圖二)。然而想要獲得高效率之元件陰極結構，只有n型摻雜是不夠的，透過研究我們發現，n型摻雜和能隙能階的產生都是獲得高效率元件陰極結構的必要條件。另外，經由價電帶電子能譜的證明，我們證實了碳酸銫對寡聚芴化物也是有效的n型摻雜物，而氧化鉬等過渡金屬氧化物則是有效的p型摻雜物，還有四氟-四氰基代對二亞甲基苯(F₄-TCNQ)則是有機物之p型摻雜物。最後我們更探討了溫度變化對寡聚芴化物能階和構形的影響，在不同溫度下蒸鍍之寡聚芴化物將會改變其分子內部不同單體單元之相對角度，在低溫時角度大約是將近垂直的狀態，但在室溫的穩定狀態下則會呈現41°的角度。而原本鹼金屬氟化物和寡聚芴化物之間會產生n型摻雜效果的反應，在低溫時將不會出現，這是因為在低溫時沒有足夠之熱能來驅使反應發生，但一旦溫度回升到室溫時，鹼金屬氟化物和寡聚芴化物之間的n型摻雜反應將會再度發生。

此論文著重討論一種新型的p型的掺雜物，過渡金屬氧化物，氧化鉬MoO₃。從OLED元件電性及紫外光電子能譜激發術(UPS)和X光電子深層電子能階譜激發術(XPS)這三種方討論氧化鉬應用於元件的原理與機制。我們發現到共蒸鍍電洞傳輸層NPB與MoO₃，將會使元件電性獲得大幅改善。從UPS可得知是因為MoO₃對NPB具有p掺雜的效果，如圖一。甚至單只用一層MoO₃放置在陽極與NPB之間，元件本身操作電壓也會下降。同時，當使用MoO₃放置在不同陽極與NPB之間，電性會趨於一致。也利用UPS證實出此種現象即是費米能階釘札 (Fermi level pinning) 所產生的效應，如圖二。

圖一、配備壓電功能的光纖束編織示意圖。雖然可製造出圓形截面的光纖，但照片中是截面形狀為長方形的光纖。

圖二、光纖製作方式示意圖。