高耐熱透明聚醚醯亞胺之合成及其應用於可撓式元件界面接著性探討

Abstract

隨著全球化跨國商務與旅遊驟增，消費者對產品之輕量性、機動性和多功能性等需求、已經帶動新世代IC產品組裝於軟性基板上，例如電子紙、衛星內可撓性的太陽能電池以及行動電話和數位相機的軟性電子組件等。雖然這些可撓性軟性基板材料具有不錯的性質，然而也有某些限制和問題急需克服，諸如過高的熱膨脹係數(CTE)、較低的玻璃轉換溫度(Tg)、較低的加工溫度、較高的氧氣和水穿透率、元件的老化以及其與障礙層、硬膜（hard coat）或者透明的導電層等多層結構的黏著力(adhesion)等。 因此本論文分為兩大部分: (一) 針對可撓性軟性基板因具較低的玻璃轉換溫度(Tg)而使得後續製程加工溫度受到限制之問題，使用兩種高分子單體(4,4'-oxydiphthalic anhydride，ODPA和2,2'-bis[4-(4-aminophenoxy)phenyl]propane， BAPP)開發具高穿透度、高玻璃轉換溫度和熱穩定性佳的聚亞醯胺薄膜，來克服可撓式元件當前所遭遇到的問題; (二) 可撓性產品因多層結構中彼此的材料性質迥異，如熱膨脹係數的差異，造成層與層間因黏著力不佳而發生彼此剝離的現象，此現象導致可撓性產品使用壽命與可靠度下降。所以提昇可撓性產品結構中層與層間的黏著性，是當前一個非常重要的課題。在本研究中利用氧氣電漿改質新穎聚亞醯胺薄膜表面的方法，改變新穎聚亞醯胺薄膜表面之化學鍵結狀態與組成成分，藉此提升透明導電層(氧化銦錫)與所合成之新穎聚亞醯胺兩者間的界面黏著性，提高可撓式產品之使用壽命與可靠度。 研究結果顯示，由於因共軛而互相堆疊的苯環會吸收可見光的藍光波段，造成聚亞醯胺薄膜呈現出黃褐顏色，但此現象也造成聚亞醯胺鏈間彼此相互吸引，使得聚亞醯胺具有良好的物性。本研究中所選用的高分子單體BAPP與ODPA，它們分別具有丙烷基與醚基，藉此可以達到降低或消除苯環間電荷轉移(Charge Transfer)的現象和提升材料之可撓性，使得其所聚合成之新穎聚亞醯胺薄膜在厚度為80um時，其透光度可達到98%以及230℃和495℃的玻璃轉換溫度和熱裂解溫度。 在第二部份裡，本研究利用X射線光電子能譜(XPS)鑑定聚亞醯胺薄膜表面的化學狀態改變。並使用四點彎曲抗折儀器(four-point bending)來量測氧化銦錫與新穎聚亞醯胺界面黏著性。研究結果顯示，聚亞醯胺的表面經過氧氣電漿改質過後，新穎聚亞醯胺表面的C-OH鍵結成分大幅增加，因而提供孤對電子(lone pair)作為載體(donor)，與氧化銦錫中的金屬原子(銦、錫)形成共軛共價鍵，而使得其與氧化銦錫界面的黏著力由未處理時之3.01 J/m2提升至8.7 J/m2 。因而證實氧氣電漿的表面改質方法確實提升了可撓式產品的壽命與可靠度。

ility, and versatility has energized a sleuth of new IC products mounted onto flexible substrates, such as e-paper, flexible solar cell in satellite, or key components using plastic substrate sin cell phones and digital cameras. While these materials offer many attractive features, they also impose limitations and challenges such as high CTE, lower Tg, low processing temperatures, problematic adhesion strength in the multiple film stacking (with barrier, hard coat, or conductive transparent oxides), high O2 and water permeation, and device degradation. Thus, there are two objections in this thesis: (1) To develop a novel flexible, polyimide substrate with high Tg in order to enable higher processing temperatures for better electric performance. A novel and transparent polyimide has been synthesized by using 4,4'-oxydiphthalic anhydride (ODPA) and 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP). (2) Due to dissimilar materials properties (E, CTE and Poisson ratio), flexible devices may induce to delaminate between layers. The behavior will decrease the lifetime of devices and low the reliability. Therefore, the adhesion of multiple-layered structure used in the typical flexible devices is a critical reliability issue. In this thesis, oxygen plasma was used to modify the surface chemical states of BAPP-ODPA polyimide. The surface modification method had enhanced the adhesion at ITO and BAPP-ODPA polyimide interface. For purpose, it could improve the lifetime and reliability of flexible devices. According to the research, the coloration of polyimide had higher light absorption at 400 nm due to the conjugation of benzene rings in stacked packing. However, the transparency of the BAPP-ODPA polyimide in the visible region was found to be 98 % because the ether linkage and bulky group in BAPP and ODPA monomers destroyed benzene stacking to minimize or eliminate charge transfe. Moreover, the BAPP-ODPA polyimide demonstrated superior thermal stability with Td at 495 ℃ and a glass transition temperature of 230 ℃. In the second part, the surface of BAPP-ODPA polyimide was modified by oxygen plasma and the changes of surface chemical states were characterized by X-ray Photoelectron Spectroscopy (XPS). The interfacial adhesive strength was determined by four-point bending system. According to the XPS results, the component ratio of C-OH increased in a great quantity by oxygen plasma. The adhesive strength of un-treatment polyimide/ITO was 3.01 J/m2. After oxygen plasma treatment, the interfacial adhesion had obviously increased to 8.7 J/m2. We could suggest that the adhesion of ITO/BAPP-ODPA polyimide improved with the increase of C-OH. The force of coordinate covalent bond was explained to help the improvement of interfacial adhesion. Because the oxygen element in C-OH bond provided a lone pair as donor to attract the metal elements in ITO structure (In, Sn), the interfacial adhesive strength between ITO and BAPP-ODPA polyimide had definitively improved by oxygen plasma treatment.