| 摘要: | 在生產微發光二極體顯示器(LED display)的眾多技術環節中，本文針對其中至為關鍵的技術-巨量轉移（Mass transfer）進行探討與改進。現行巨量的轉移技術中，本文以雷射正向轉移（Laser-induced forward transfer，LIFT）技術為基礎，進行改良研究。我們從在藍膠帶(Blue tape)上的陣列LEDs出發，將LEDs轉移到最終的目標基板上(Destination substrate)。全程包含膠黏轉移與雷射轉移兩個轉移過程：前者，是將LEDs從藍膠帶上轉移到過渡基板(Transition substrate)之犧牲層(Sacrificial layer)上；後者，再將LEDs轉移到目標基板上。
首先，有別於一般常用的UV雷射光源，我們選用適合工業量產、紅外光奈秒脈衝期的光纖雷射；其次，針對國內廠商自行研發的犧牲層材料，稱為光吸收膠(Light Absorbing Polymer Glue, LAPG)，以單層與雙層結構形式進行膠黏轉移作詳細的實驗與分析，從分析結果中選取理想的LAPG配方與結構層數，供後續的LIFT製程使用；接著，嘗試不同的LAPG膜厚、雷射功率與重複率等三個參數組合，檢視LIFT之轉移成果；最後，以隨機森林 (Random forest) 方法分析LIFT過程中此三個參數，成功找出參數間的重要相關性排序。
結果顯示，本研究提出的雷射轉移配置可成功將對LEDs做大量的轉移，此法也可作選擇性、個別LED之局部轉移。將轉移後的LEDs與微米銅導線串聯接電，發光測試顯示經 LIFT轉移後之LEDs在全程轉移過程功能完整。最後，隨機森林方法分析顯示，在目前的架構與實驗方法下，LAPG之膜厚與LIFT轉移成功的關聯性最高。
;Micro-LED (µLED) is a very promising technology for creating highly efficient and great looking flexible displays. It, however, includes numerous sophisticated apparatuses that involve complex processes. One of the critical challenges for the commercialization of LED display technology is to develop a cost-effective method for transferring massively LEDs. Among the competitive mass transfer techs of µLED, this study aims at facilitating the laser-induced forward transfer (LIFT) technology. Transferring an array of µLEDs from a blue tape to the final destination substrate includes two steps: adhesive transfer and laser transfer. The former is to move µLEDs from the blue tape to the the sacrificial layer on a transition substrate; the latter, then transfer them to the destination substrate.
Firstly, instead of the UV laser, a commonly used light source in LIFT, we use a infrared fiber laser, with nano-second pulse duration, that is cost effective and popular in the industry. Secondly, the adhesive transfer process is tested based on the composition and thickness of the sacrificial layer. Its materials are developed by a domestic manufacturer, hereby named as the light absorbing polymer glue (LAPG). The recipes for LAPG and various thicknesses for the sacrificial layer that are achievable for effective adhesive transfer are obtained for the subsequent LIFT process. Thirdly, the LIFT transfer results based various parameters of the LAPG film thickness, laser power and repetition rate are examined. Finally, the random forest method is used to analyze the three parameters in the LIFT process and the priority of their importance is determined.
Results show that the proposed LIFT scheme can successfully transfer massively LEDs to the destination substrate. In addition, this method has the advantage of local transfer, moving an individual LED to a specified location. The lighting test is executed by connecting the transferred LEDs in series on a test pad that consists of two copper lines linking the LEDs’ anode and cathode, respectively. It proves that the LEDs function is well preserved throughout the transfer process. Finally, the random forest analysis shows that, under the current experimental configuration, the film thickness of LAPG is the most relevant to the success of LIFT transfer. |
