Nonvolatile memory devices based on polyimides bearing noncoplanar twisted biphenyl units containing carbazole and triphenylamine side-chain groups
作者:Yue-Qin Li、Run-Chen Fang、An-Min Zheng、Yue-Ying Chu、Xian Tao、Hui-Hua Xu、Shi-Jin Ding、Ying-Zhong Shen
DOI:10.1039/c1jm12453f
日期:——
Two novel polyimides, PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA), consisting of alternating electron-donating 2,2′-bis[4-(9H-carbazol-9-yl)phenyl]- or 2,2′-bis[4-(diphenylamino)phenyl]-substituted biphenyl moieties and electron-accepting phthalimide moieties were synthesized and characterized. These polyimides are thermally stable with 5% weight loss over 500 °C and the glass transition temperatures of the polyimides were found to be 293 °C. The optical band gaps of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were 3.42 and 3.30 eV, respectively, indicating the significance of the linkage groups. The estimated energy levels (HOMO, LUMO) of PI(CzBD-BTFBPDA) and PI(TPABD-BTFBPDA) were (−5.51, −2.10) and (−5.22, −2.02) eV, respectively. Resistive switching devices with the configuration of Al/polymer/ITO were constructed from these polyimides by using the conventional solution coating process. The as-fabricated PI(CzBD-BTFBPDA) film exhibited a nonvolatile bipolar write-once–read-many times (WORM) memory character, whereas devices with the PI(TPABD-BTFBPDA) film showed “write–read–erase” flash type memory capability. The ON/OFF current ratios of the devices were both around 106 in the ambient atmosphere. The mechanisms associated with the memory effect were further elucidated from the density functional theory (DFT) method at the B3LYP level with the 6-31G(d) basis set. The present study suggested that the tunable switching behavior could be achieved through the appropriate design of the donor–acceptor PIs structure to have potential applications for memory devices.
合成并表征了两种新型聚酰亚胺 PI(CzBD-BTFBPDA)和 PI(TPABD-BTFBPDA),它们由交替的电子捐赠型 2,2′-双[4-(9H-咔唑-9-基)苯基]-或 2,2′-双[4-(二苯基氨基)苯基]-取代联苯分子和电子接受型邻苯二甲酰亚胺分子组成。这些聚酰亚胺具有热稳定性,在 500 °C 以上重量损失率为 5%,聚酰亚胺的玻璃化转变温度为 293 °C。PI(CzBD-BTFBPDA) 和 PI(TPABD-BTFBPDA) 的光带隙分别为 3.42 和 3.30 eV,表明了连接基团的重要性。PI(CzBD-BTFBPDA) 和 PI(TPABD-BTFBPDA) 的估计能级(HOMO、LUMO)分别为 (-5.51, -2.10) 和 (-5.22, -2.02) eV。采用传统的溶液涂覆工艺,用这些聚酰亚胺构建了铝/聚合物/ITO 配置的电阻开关器件。制备的 PI(CzBD-BTFBPDA)薄膜具有非易失性双极一次写入-多次读取(WORM)存储器特性,而 PI(TPABD-BTFBPDA)薄膜器件则具有 "写入-读取-擦除 "闪存类型存储器能力。在环境气氛中,器件的导通/关断电流比都在 106 左右。通过密度泛函理论(DFT)方法,在 6-31G(d) 基集的 B3LYP 水平上进一步阐明了与记忆效应相关的机制。本研究表明,通过适当设计供体-受体 PIs 结构,可以实现可调开关行为,从而有望应用于存储器件。