title: Clues to the electrical switching mechanism of carbazole-containing polyimide thin films.
abstract: 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.
authors.affiliation: 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.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Ree
authors.forename: Wonsang
authors.initials: W
authors.lastname: Kwon
authors.forename: Kyungtae
authors.initials: K
authors.lastname: Kim
authors.forename: Yong-Gi
authors.initials: YG
authors.lastname: Ko
authors.forename: Young Yong
authors.initials: YY
authors.lastname: Kim
authors.forename: Hoyeol
authors.initials: H
authors.lastname: Lee
authors.forename: Moonhor
authors.initials: M
authors.lastname: Ree
keywords: carbazole distribution denpendency; carbazole population dependency; carbazole-containing polyimide; charge hoping process; charge-trap; digital memory device; film thickness dependency; memory mechanism; nonvolatile memory characteristics