- 學位論文
先進可撓式多層薄膜基板之力學設計與結構敏感度分析
Mechanical Design and Structural Sensitivity Analysis of Advanced Flexible Substrate with Multi-Thin Films
摘要
軟性可撓式元件具備重量輕、高色彩等特點，為未來最具潛力之顯示技術之一。對於下一世代可撓式顯示元件應用，顯示面板隨應用產品的需求被要求需能承受某種程度大小之撓曲。由力學角度觀之，於多層堆疊之薄膜平板受到過大之撓曲負載，可撓封裝結構將趨於破壞。在結構厚度方向上考量有一不受曲率半徑大小而變形區域，即應變為零之處，稱之為中性軸平面。由於軟性可撓式顯示元件封裝結構中，有機發光二極體元件扮演重要角色，若中性軸平面位置能座落於有機發光二極體元件，整體封裝結構將可承受任意之撓曲條件。 本研究討論軟性可撓式有機發光二極體元件在施加不同曲率半徑負載條件下，內部所受之最大撓曲應力而造成其封裝結構破壞情形。藉由相關力學理論分析推論軟性可撓式顯示器可能失效情形。採用有限元素法之數值模擬分析，討論多層薄膜幾何尺寸及其機械性質進行一系列參數化模擬，了解其多層結構與觀察有機發光二極體元件之受力情形。當元件受最大撓曲應力超過其降伏強度將可能導致破壞失效；此外，推導多層薄板分析理論了解各層薄膜應力分佈與模擬預測方法加以比較，發現模擬預測分析與理論計算結果曲線相互吻合；並將模擬方法與實驗資料相互驗證，以獲得具有高度可信賴的應力模擬分析結果。本研究指出，將金屬覆蓋層用塑膠基板取代將有較佳之力學表現行為。再者，亦使用因子設計分析，將金屬覆蓋層厚度、金屬覆蓋層楊氏係數、塑膠基板厚度、黏著層厚度，以及塑膠基板楊氏係數等五個因子進行兩水準分析，設計軟性可撓式顯示元件之優化結構。分析指出，可撓封裝之多層薄膜為較柔軟材料與厚度較薄時，中性軸位置將最接近有機發光二極體元件，致使有機發光二極體元件不受外力而失效。 希望藉由本論文之模擬分析結果，能夠幫助軟性可撓式顯示元件結構設計上之提升，建立相關力學結構分析資料庫，作為下一世代之軟性可撓式封裝結構設計之研究參考。
並列摘要
Flexible device is one of the most potential display technologies in the future because of its advantages having light weight and high colorful characteristics. For the applications of next generation flexible display devices, they are required to satisfy certain degrees of deflections within electronic products. From the viewpoint of basic mechanics, multi-stacked thin films overloaded with an external bending force tend to failures. Consequently, arranging organic light-emitting diodes (OLED) in neutral axis (N.A.) along thickness direction where is regarded as stress-free in flexible encapsulation structure is an important matter to meet the requirements of that a whole flexible OLED encapsulation structure could suffer arbitrary flexural loading conditions. From the above-mentioned explanations, this thesis investigates the failure possibilities of flexible organic light-emitting diodes (FOLED) induced by maximum bending stresses resulted from the use of various bending radiuses of curvature. The derived mechanical theories combined finite element simulations (FEM) are utilized to perform a series of parametric analyses regarding geometrical dimensions and mechanical properties of multi-stacked films in OLED devices. Predicted flexural stresses are compared with yield strengths of concerned film materials to judge the failure occurrence of OLED devices. In additions, through the helps of derived analytical solutions and related experimental data, the results validation of FEM is obtained and proved to be highly reliable. This research indicates that replacing a cover plate by a plastic substrate would improve mechanical performances of flexible OLED encapsulation. Moreover, a full factorial design with two levels is implemented to find an optimal OLED structure by considering five designed factors such as the thickness and Young’s modulus of the cover plate, adhesive thickness, and the thickness and Young’s modulus of the plastic substrate. The analytic results reveal that as a flexible encapsulation with stacked thin films becomes softer and thinner, the locations between N. A. and OLED component would be closer. Consequently, both the OLED lifetime and mechanical reliability of flexible structure could be raised, respectively. Through the simulation results provided by this investigation, we hope it valuable to enhance the structural design of flexible OLED devices. In addition, the database establishment of relative materials and structural models are beneficial to be the reference for the developments of next generation flexible OLED devices.