本场演讲者郑克勇教授

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

台湾大学光电所 苏国栋教授

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.

利用高分辨率同步辐射光源之光电子发射能谱，本论文将有系统地研究寡聚芴化物(oligofluorenes)(图一)之电子结构、界面化学以及变温特性。首先，我们观察并归纳出寡聚芴化物的能阶结构和许多重要的特性，包括游离能、界面电偶极和发光能隙，同时我们也在这一系列寡聚芴化物中发现到一些规则性的趋势。而根据本篇论文的研究，寡聚芴化物的支链取代物将会大幅地影响到其电子和光学特性，寡聚芴化物之组件操作性能，也会受到支链取代物的影响。为了让寡聚芴化物组件之电子注入能障降低，并且提升电子在阴极界面的注入效率，氟化锂和氟化铯等碱金属氟化物将被用作为寡聚芴化物之n型掺杂物，这两样n型掺杂物都能够与寡聚芴化物反应并造成n型掺杂的结果，但却不需要铝的存在，这使得寡聚芴化物组件在阴极金属的使用上有了更多的选择(图二)。然而想要获得高效率之组件阴极结构，只有n型掺杂是不够的，透过研究我们发现，n型掺杂和能隙能阶的产生都是获得高效率组件阴极结构的必要条件。另外，经由价电带电子能谱的证明，我们证实了碳酸铯对寡聚芴化物也是有效的n型掺杂物，而氧化钼等过渡金属氧化物则是有效的p型掺杂物，还有四氟-四氰基代对二亚甲基苯(F₄-TCNQ)则是有机物之p型掺杂物。最后我们更探讨了温度变化对寡聚芴化物能阶和构形的影响，在不同温度下蒸镀之寡聚芴化物将会改变其分子内部不同单体单元之相对角度，在低温时角度大约是将近垂直的状态，但在室温的稳定状态下则会呈现41°的角度。而原本碱金属氟化物和寡聚芴化物之间会产生n型掺杂效果的反应，在低温时将不会出现，这是因为在低温时没有足够之热能来驱使反应发生，但一旦温度回升到室温时，碱金属氟化物和寡聚芴化物之间的n型掺杂反应将会再度发生。

此论文着重讨论一种新型的p型的掺杂物，过渡金属氧化物，氧化钼MoO₃。从OLED组件电性及紫外光电子能谱激发术(UPS)和X光电子深层电子能阶谱激发术(XPS)这三种方讨论氧化钼应用于组件的原理与机制。我们发现到共蒸镀电洞传输层NPB与MoO₃，将会使组件电性获得大幅改善。从UPS可得知是因为MoO₃对NPB具有p掺杂的效果，如图一。甚至单只用一层MoO₃放置在阳极与NPB之间，组件本身操作电压也会下降。同时，当使用MoO₃放置在不同阳极与NPB之间，电性会趋于一致。也利用UPS证实出此种现象即是费米能阶钉札 (Fermi level pinning) 所产生的效应，如图二。

图一、配备压电功能的光纤束编织示意图。虽然可制造出圆形截面的光纤，但照片中是截面形状为长方形的光纤。

图二、光纤制作方式示意图。