- 學位論文
壓印技術應用於氮化鎵發光二極體之研究
A Study of Imprint Lithography Applied to GaN-based Light-Emitting Diode
摘要
本篇論文最主要的目的是將旋塗玻璃 (Spin on Glass, SOG)的微米/次微米結構利用熱壓印方法製作於打線封裝的發光二極體晶片(Light Emitting Diode, LED)表面，藉此來提升發光二極體之光萃取效率及解決電特性不佳的問題，並同時探討壓印SOG微結構的成型方式及各壓印參數(脫模、壓印力、壓印溫度)對壓印製程之影響。在壓印SOG的方式上，可以分為兩種，其一為高壓常溫法，其二為低壓高溫法，兩種方式均各有利弊，高壓常溫法容易將晶片壓碎；低壓高溫法所需製程時間長且需解決升溫後的熱效應問題。除此之外，SOG 經過高溫處理之後，特性近似二氧化矽(Silicon Dioxide, SiO2)，具備化學及物理的穩定性且機械性質佳，可為發光二極體晶片提供一定程度的封裝保護，且SOG表面能較其他常使用之壓印材料低，搭配脫模劑(Polytetrafluoroethylene, PTFE)和模仁本身之特性，可以有效壓印出完整結構。經本論文討探後，利用壓印方式所製作之發光二極體對於兼顧電性與光性是可以達成的。在提升光萃取效率上，因為SOG之折射率(n=1.5)介於空氣(n=1)與氮化鎵(n=2.4)之間，漸變式折射率對於提升晶片的光萃取效率有直接的影響，而依據壓印所製作的微米/次微米各式結構，可有效的提升LED晶片的光萃取效率，而製程之後發光二極體在電流20 mA的順向電壓依舊維持3.3 V，足可證明電特性並未因此而受到影響。
並列摘要
In this study, a hot embossing technique has been used to make micron/sub-micron structures on wire bonding light emitting diode (LED) to improve light extraction efficiency and also avoid the damage of electrical performance. The imprinting material is spin on glass (SOG). The characteristics of SOG are similar to SiO2 after annealing. It has good chemical and physical stabilities and mechanical strength compared to conventional imprinting polymers. There are two types to imprint SOG, one is the high-pressure with low-temperature and the other is low-pressure with high-temperature way. The high-pressure way will induce the chip crack easily; and the low-pressure one will yield a better imprinting structure but need a longer process time. The refractive index of SOG is ~1.5 which is between GaN (~2.4) and air, so it will reduce the reflection from LED. Meanwhile, the light extraction efficiency will also increase due to the micron/sub-micron structures on LED to ruin the total internal reflection. The forward voltage of our LED after embossing processing can still be maintained at 3.3 V under 20 mA injection.