以低溫電漿輔助化學氣相沉積多層碳氮化矽/電漿聚合高分子水氣阻障膜

Abstract

可撓式有機發光二極體，是近年來新興的技術，因其優異的外型以及行動性，極可能成為下一世代的顯示器及照明。但是可撓式有機發光二極體其使用的塑膠基板，有著相當高的水氣、氧氣滲透率，穿透過的水氧會和元件內部的陰極產生反應，造成嚴重的破壞。因此為了達到10,000小時以上的壽命，勢必要在塑膠基板上鍍上一層高阻水阻氣、高透光度的薄膜。 本研究使用的水氣阻障層，碳氮化矽、聚甲基丙烯酸甲酯多層結構，以低溫電漿輔助化學沉積法，在軟性塑膠基板－聚對苯二甲酸乙二酯上成功得被開發出來，並用於有機發光二極體的封裝。首先吾人探討由不同的前驅物N-Methyl-Aza-2,2,4-Trimethylsilacyclopentane (MTSCP) 和1,3,5-Trimethyl-1,3,5-Trivinylcyclo-Trisilazane (VSZ) 所製備的碳氮化矽，其缺陷密度與水氣擴散速度(WVTR)的關係，吾人發現由MTSCP所沉積的碳氮化矽，其缺陷密度相較於VSZ所沉積的碳氮化矽少，因此阻障效果有較好表現;另外也發現有機層PPMMA相較於PPS，其薄膜密度較高、對水氣的溶解度少，阻障效果也比較優異。接著探討無機/有機複合薄膜，其增加層數對於延遲時間及水氣擴散速度的貢獻。發現每增加一層，水氣達到飽和的時間要延長20%，其在這段區域的WVTR也會大幅下降，但是對於穩定態的擴散速度影響較少。三層SiCxNy/PPMMA結構，其WVTR可以達到9×10-4 g/m2/day、延遲時間13小時，但是光穿透度由89%下降到70%。最後我們製備四層的水氣阻障薄膜，其WVTR估計為5×10-4 g/m2/day用於有機發光二極體的封裝，在起始亮度4000 cd/m2下，亮度衰減至一半的壽命可達93.3小時，換算成起始亮度500 cd/m2，壽命約為3200小時(133天)，相較於裸PET封裝多了70%。

Flexible organic light emitting diode (FOLED) is an emerging technology of next-generation display and lighting for its excellent form factor and mobility. However, FLOED suffers a shortcoming that the oxygen and water permeating through plastic substrate at a relatively high rate, can react with the cathode, resulting in severe degradation. Therefore, high WVTR (water vapor transmission rate) performance barrier films with high transmittance and 10,000-hr lifetime are required for FLOED application. In this thesis, a multi-layered structure of SiCxNy/PPMMA (plasma polymerized methyl methacrylate) deposited on flexible PET substrate by PECVD at low temperature has been successfully developed to passivate OLED devices from moisture. In specific, two different precursors, N-Methyl-Aza-2,2,4- trimethylsilacyclopentane (MTSCP) and 1,3,5-trimethyl-1,3,5-trivinylcyclo- trisilazane (VSZ) were used for the deposition of SiCxNy film, while methyl methacrylate and styrene monomer were used as the precursor for PPMMA and plasma-polymerized polystyrene (PPS) films, respectively. The correlation between WVTR and the pinhole density of SiCxNy films using two different precursors were examined. It was found that MTSCP-derived SiCxNy film possessed better barrier effectiveness, i.e. WVTR because of its lower pinhole density compared to VSZ-derived film. Moreover, the WVTR of organic layer, PPMMA film was better than PPS film, due to its higher film density and small moisture solubility. The effect of inorganic/organic layer pairs was further studied to understand their contributions in the lag-time and WVTR. It was found that one additional pair of SiCxNy/PPMMA layers can extend the lag-time by 20% and reduce WVTR significantly within lag-time region, but has less effect in steady-state WVTR region. Three pairs of SiCxNy/PPMMA can reduce WVTR down to 9×10-4 g/m2/day, with a lag-time of 13 hours. The four-pair SiCxNy/PPMMA barrier stack on PET with an estimated WVTR of 5×10-4 g/m2/day was used to passivate an OLED lighting device. At an initial luminance of 4000 cd/m2, the operational half-lifetime was 93.3 hrs and an estimated lifetime of 3200 hrs (133days) at 500 cd/m2 was calculated, which was 70% longer than bare PET passivation.