CF4 電漿處理對可撓式聚對苯二甲酸乙二酯基材水氣穿透率之影響

Abstract

隨著科技的進步，輕、薄、短小、低成本成為主要的訴求，在這樣需要下，可撓式元件逐漸被重視，雖然高分子基材已經成功應用在可撓式元件上，但當有機物加入可撓式元件時，高分子基板的高水氣穿透率(WVTR)是一個缺點。水氣會和撓式元件中的有機物反應，造成可靠度以及電性逐漸變差的問題，因此尋找方法以降低高分子基板的水氣穿透率是急切的議題。 文獻中已經證實，高分子的氟化處理會使得高分子的表面有疏水的性質，這啟發了我們可以應用斥水的特性來降低高分子的水氣穿透率。吾人以聚對苯二甲酸乙二酯(PET)作為高分子基板，利用CF4電漿完成PET的氟化處理，以鈣腐蝕(Ca test)量測水氣穿透率。在氟化處理之後，吾人對PET做一系列包含表面形貌、潤濕性、化學組成的觀察，吾人發現氟化處理之後， PET表面的疏水特性是由於PET表面形成了一層氟化基層。氟化處理前PET的水氣穿透率為2.7g/m2-day；電漿氟化處理15分鐘之後降為0.43g/m2-day。石英微天秤分析發現，氟化後的PET有較低的水氣吸附量以及水氣擴散係數。利用吸附-擴散的理論，由於PET表層形成了氟化基層而有較低的水氣吸附量及擴散係數，因此氟化處理之後可以有效的降低水氣穿透率。為了延展疏水的特性，吾人在PET的表面加入有序列的圖騰(regular pattern)，同時電漿氟化處理15分鐘，雖然成功增加疏水性，但PET的水氣穿透率為0.82 g/m2-day，這是因為regular pattern提供了自由表面使水氣可以吸附於表面。

As the technology progresses continuously, the requirements such as light weight, smaller size, high mobility, and low cost have become a main pursuit. Under such circumstance, flexible devices then received great attention recently. Polymer substrates had been applied in flexible devices and obtained some success. However, the innate drawback that the polymers had high water vapor transmission rate (WVTR) would be magnified especially the organic material was introduced to flexible devices. The reactions between the organic material and water vapor would cause the reliability issues and electrical degradation. It had become an inevitable issue to explore a way to decrease the WVTR of polymer substrate. Fluorination of polymer would lead to a hydrophobic surface and had been demonstrated by literature researches. This inspired us to apply the water-repellency characteristic to improve the WVTR of polymer substrate. In this thesis, polyethylene terephthalate (PET) was selected to be the polymer substrate because it had been widely applied as flexible substrate. CF4 plasma was adopted to complete the fluorination of PET. In addition to study the difference of WVTR based on Calcium corrosion test (Ca test) after the plasma process, we also revealed the comprehensive observation of the fluorination of PET such as surface morphology, wetting ability and chemical composition. It’s found that the surface of PET became hydrophobic due to the highly fluorinated functionalities formed on the surface. The WVTR decreased from 2.7 to 0.43 g/m2-day which indicated a significant reduction (84%) was achieved for CF4 plasma-treated PET (60 W, 15 minutes) film. According to the Quartz crystal microbalance (QCM) analysis, the lower moisture absorption and diffusion constant which improve the transportation behavior of water vapor through the PET based on solution–diffusion model. To extend the category of research, we further increase the hydrophobicity of PET surface with fluorinated regular pattern. Instead of exhibiting expected outcome, WVTR for regular pattern with 15 minutes CF4 plasma treatment was evaluated to be 0.82 g/m2-day due to the much increased of free surface which the water vapor could adsorb.