大氣電漿技術對有機薄膜電晶體特性改善之研究

Abstract

透過旋轉塗佈的方式沉積可溶性共軛高分子，對於製作大面積且低成本的有機薄膜電晶體元件有很大的應用潛力。由於有機薄膜電晶體的效能與半導體及介電層的界面有很大的關係，所以此篇論文的研究目的是藉由控制半導體與介電層之間的界面化學特性，來改善以聚(3-烷基噻吩)作為半導體層的有機薄膜電晶體之特性。因為二氧化矽作為介電層已行之有年，材料特性較易掌控且界面改質容易，因此我們選擇熱氧化方式沉積二氧化矽作為我們的介電層，而由於高規則度聚(3-烷基噻吩)具有較高的結晶排列性，使薄膜電晶體元件能獲得較佳的電子遷移率，所以在此作為我們元件的半導體層。利用六甲基二矽氮烷對二氧化矽絕緣層進行表面處理，已證實對聚(3-烷基噻吩)薄膜電晶體的特性有明顯的改善，而本論文則透過常壓式電漿製程將六甲基二矽氮烷沉積於聚(3-烷基噻吩)與二氧化矽絕緣層間的界面，並探討此種表面處理製程對有機薄膜電晶體效能的影響。常壓電漿系統是一種可以將製程溫度操控於120度以下的低溫，並可工作於一般大氣壓力之下。利用常壓式電漿製程進行表面處理後，有機薄膜電晶體元件的臨界電壓可被降至-10伏特以內，載子遷移率也比沒經表面處理的元件提昇15倍以上，約為0.02-0.03 cm2/Vs，其效果甚至比透過旋塗式或蒸鍍等表面改質方法還好。本論文已證實常壓式電漿系統，確實是一種低溫且高效率的有機薄膜電晶體元件界面改質製程。

Organic thin film transistors made by spin-coating from solution- processable conjugated polymers have potential advantages in fabricating low-cost devices with large areas. Since OTFT performance depends strongly on the interface between the semiconductor and the dielectric layer, this study attempts to demonstrate that the characteristics of P3HT-based OTFT are improved by controlling the chemistry of the dielectric/polymer interface. Thermal SiO2 is adopted as the dielectric because of its well-characterized properties and ease of chemical modification. Regioregular P3HT (of which HT linkages represent more than 98.5% of the linkages) is utilized as the active layer, so it exhibits better ordering and crystallinity in the solid state, and substantially improved electroconductivities. The field-effect mobility was markedly improved by modifying the surface of SiO2 with using a hexamethyldisilazane (HMDS) self-assembled monolayer. Before the active layer was deposited, the surface of SiO2 was modified using atmospheric-pressure plasma technique (APPT). APPT is a new process that can be implemented at atmospheric pressure and at low temperature. The steps of APPT are performed below 120°C and at atmospheric pressure, so the approach is very suited to use on a plastic substrate. After the SiO2 surface has been modified by the APPT process with hexamethyldisilazane (HMDS), it exhibits typical I-V characteristics of TFTs. Calculations reveal that its field effect mobility can reach 0.02-0.03 cm2/Vs, which is about 15 times that before the modification, and the threshold voltage is below -10V. The performance is even better than that obtained following the usual surface treatment of the SiO2 surface by spin-coating or evaporation. This work suggests an interesting direction for preparing high-performance OTFTs with high efficiency and low-temperature surface treatment by APPT.