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.

Triggering WORM/SRAM Memory Conversion in a Porphyrinated Polyimide via Zn Complexation as the Internal Electrode

“…To achieve electrical bistability, aromatic polyimides (PIs) containing electron donor (D) and acceptor (A) within a single macromolecular chain have nowadays been the major topic of interest among researchers. ,− In addition to the intrinsic merits such as high-temperature stability, structure diversity, and chemical resistance, these D–A PIs could readily form conjugated structures for charge transfer (CT), which then contribute to electronic transitions between the ground and excited states through induced CT complex, resulting in desirable memory effect. ,, The memory type is determined by the stability of the formed CT complex, which could be tuned by altering the electron pull-push effect between D and A . To this end, various electron-donating species with different strength, including triphenylamine, ,− carbazole, − ferrocene, , oxadiazole, , pyrene, , and anthracene, , have been utilized and polymerized into the PI chain as electron donor. The synthesized PIs witness the achievement of memory behaviors from the volatile dynamic random access memory (DRAM) and static random access memory (SRAM) to the nonvolatile flash and write once read many times memory (WORM) upon structural variation, revealing the significance of the electron-donating moieties. ,, However, due to the limited variety of D species, the design of electroactive PIs with wanted memory characteristic is severely restricted.…”

Nonvolatile resistive memory devices based on ferrocene‐terminated hyperbranched polyimide derived from different dianhydrides

“…Among them, polyimides (PIs) gradually come to the fore due to their superior thermal stability and chemical resistance, coupled with favorable electrical properties . For memory devices based on functional PIs, the switching behaviors mainly arise from charge transfer between an electron‐accepting moiety (A), imide ring, and an electron‐donating moiety (D) such as triphenylamine, carbazole, and sulfur‐containing moiety …”

New photopatternable polyimide and programmable nonvolatile memory performances

“…[21][22][23][24][25] Although some of these materials have high dimensional and mechanical stability, their film forms are not sufficiently resilient to survive the device fabrication process. [31][32][33] Furthermore, they all lack patternability and thus can be patterned only with the aid of photoresist-based lithography techniques, significantly increasing the number of steps and the cost of device fabrication. Therefore, there is still an urgent need for low-cost printable, patternable, multi-stackable memory materials that are suitable for the fabrication of high-density memory devices and further integration with other electronic devices of various functionalities.…”