The Application of Aluminum Nitride on Pentacene Based OTFTs
另外，我們觀察到氮化鋁的表面能因環境的碳吸附將會隨著置放時間不同而有所改變，愈長的置放時間其表面能愈低。並且在我們的研究中亦發現，五苯環成長在碳吸附量較大而表面能較低的表面上有較好的元件特性，其元件的載子遷移率隨著置放時間增加而增加；在此研究當中發現，元件置放14天其場效載子遷移率將由0.05 cm2/Vs 增加至 0.67 cm2/Vs。究其原因，是由於表面的碳吸附降低了氮化鋁的表面能，導致pentacene在初期成長的覆蓋率增加，因此改善了載子遷移率。|
The study of pentacene based organic thin film transistors (OTFTs) has been a major area of research on organic semiconducting materials and devices. OTFTs have many advantages such as low process temperature, low cost and simple process fabrication, structure flexibility. However, the high operating-voltage remains a limitation on organic transistors. To lowering the operating-voltage, a high-k materials, aluminum nitride (AlN), has been proposed as a low operating-voltage gate-dielectrics in pentacene based OTFTs. This work was studied with my senior classmate, Cheng-Wei Chou. In this thesis, the AlN dielectric application and aging effect in pentacene based OTFTs are reported. To prevent cross-talk between transistors in close proximity and to achieve a low off-current in OTFTs array, it is necessary to pattern the organic semiconductor layer. A pentacene patterning method on the AlN dielectric surface that can be combined with conventional lithography to pattern pentacene film was reported. The AlN surface was patterned using a conventional photo lithography process and then treated with oxygen (O2) plasma on uncovered AlN to modify surface polarity. The surface energy of O2 plasma treated region was increased drastically. Following pentacene deposition, the sample was dipped in water to remove pentacene from the O2 plasma treated area. The polar surface energy was attributed to the increase of Al-O bonds on the surface based on XPS measurements. The enhancement of the polar surface energy explains the water-removable pentacene patterning mechanism. Likewise, the lowered AlN surface energy over time when the AlN film stored aged in a non-vacuum environment was observed. To confirm the AlN aging effect, the relationship between the aged AlN film and the pentacene based OTFTs were demonstrated in this thesis. The lowered surface energy over the aging time was due to the carbon absorption on the AlN surface. Pentacene based OTFTs fabricated on the aged AlN surface showed a higher performance in electrical characteristics. The mobility was enhanced from 0.05 cm2/Vs to 0.67 cm2/Vs with the limited aging time (14 days). This improved mobility was due to the carbon accumulation on the AlN surface, lowers the surface energy and increased the pentacene coverage in the first few layers.
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