Department of Chemistry, Division of Advanced Materials Science, Center for Electro-Photo Behaviors in Advanced Molecular Systems, Pohang Accelerator Laboratory, Polymer Research Institute, and BK School of Molecular Science, Pohang University of Science & Technology (POSTECH) , Pohang 790-784, Republic of Korea.
ACS Appl Mater Interfaces. 2014 Dec 10;6(23):21692-701. doi: 10.1021/am506915n. Epub 2014 Nov 26.
The mechanism behind electrical memory behavior of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoro-isopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal properties, band gaps, and molecular orbital levels of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. PI Devices were fabricated with aluminum electrodes and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was driven by trap-limited space-charge limited conduction and ohmic conduction. The permanent memory characteristics were found to be attributed to the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the backbone is not conjugated, the present results collectively indicate that the electrical switching behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.
研究了含咔唑的聚酰亚胺（PI）在纳米薄膜中的电记忆行为背后的机制。为此，我们合成了一系列聚（3,3'-二羟基-4,4'-联苯-3,3'-双（N-乙烯基氧羰基）咔唑-4,4'-联苯六氟异丙叉二邻苯二甲酰亚胺）（6F-HAB-HABCZn-PI）作为含咔唑聚合物体系的模型。测定了 PI 的热性能、带隙和分子轨道能级。此外，还分析了化学组成以及纳米薄膜形貌和电子密度，提供了关于咔唑部分在 PI 薄膜中的存在和位置分布的详细信息。用铝电极制备了 PI 器件并进行了电测试。器件中的 PI 薄膜层表现出由陷阱限制的空间电荷限制传导和欧姆传导驱动的电永久记忆行为。发现永久记忆特性归因于掺入的咔唑部分，而不是其他化学组分。此外，记忆特性与 PI 层中咔唑部分的数量和位置分布以及薄膜厚度密切相关。考虑到主链不共轭，目前的结果表明，PI 薄膜的电开关行为是由咔唑部分作为电荷陷阱驱动的，并且咔唑电荷陷阱位点作为跃迁点的跳跃过程。
