Department of Chemical and Biological Engineering, Hanbat National University , Daejeon 305-719, Korea.
Department of Nano, Medical, and Polymer Materials, Yeungnam University , Gyeongsan 712-749, Korea.
ACS Appl Mater Interfaces. 2015 Nov 18;7(45):25045-52. doi: 10.1021/acsami.5b08414. Epub 2015 Nov 4.
Understanding charge trapping in a polymer dielectric is critical to the design of high-performance organic field-effect transistors (OFETs). We investigated the OFET stability as a function of the dielectric polymer stereostructure under a gate bias stress and during long-term operation. To this end, iso-, syn-, and atactic poly(methyl methacrylate) (PMMA) polymers with identical molecular weights and polydispersity indices were selected. The PMMA stereostructure was found to significantly influence the charge trapping behavior and trap formation in the polymer dielectrics. This influence was especially strong in the bulk region rather than in the surface region. The regular configurational arrangements (isotactic > syntactic > atactic) of the pendant groups on the PMMA backbone chain facilitated closer packing between the polymer interchains and led to a higher crystallinity of the polymer dielectric, which caused a reduction in the free volumes that act as sites for charge trapping and air molecule absorption. The PMMA dielectrics with regular stereostructures (iso- and syn-stereoisomers) exhibited more stable OFET operation under bias stress compared to devices prepared using irregular a-PMMA in both vacuum and air.
了解聚合物电介质中的电荷俘获对于高性能有机场效应晶体管（OFET）的设计至关重要。我们研究了栅极偏置应力和长期操作下介电聚合物立体结构对 OFET 稳定性的影响。为此，选择了具有相同分子量和多分散指数的等规、间规和无规聚甲基丙烯酸甲酯（PMMA）聚合物。PMMA 立体结构显著影响聚合物电介质中的电荷俘获行为和陷阱形成。这种影响在体区比在表面区更为强烈。PMMA 主链上侧基的规则构象排列（等规＞间规＞无规）促进了聚合物链间的紧密堆积，并导致聚合物电介质具有更高的结晶度，从而减少了作为电荷俘获和空气分子吸收位点的自由体积。与使用不规则 a-PMMA 在真空和空气中制备的器件相比，具有规则立体结构（等规和间规异构体）的 PMMA 电介质在偏置应力下表现出更稳定的 OFET 操作。
