Polymer memory devices with widely tunable memory characteristics based on functional copolynaphthalimides bearing varied fluorene and triphenylamine moieties

• Polymer memories with widely tunable memory effects were achieved based on co-PNIs.
• The memory behavior was modulated from non-conducting, to SRAM and to WORM.
• Electronic structure and property variations were explored by quantum calculation.
• The memory conversion is ascribed to enhanced ability to form stable CT complexes.

For producing flexible memory materials with controlled memory characteristics, functional copolynaphthalimides (co-PNIs), with varied composition of 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-(9-fluorenylidene) dianiline (BAPF) and 4,4′-diaminotriphenylamine (DATPA), were designed and synthesized in this work. Optical and electrochemical measurements on the synthesized co-PNIs, denoted as co-PNI-TPAx (where x = 0, 1, 2, 5, 10 for the molar ratio of the DATPA-containing unit in the co-PNIs), indicate gradually enhanced HOMO and continually degraded band gap with increasing DATPA unit, as further approved by molecular simulation. What is more, electrical characterization on the ITO | thin co-PNI active layer | Al sandwich devices witnesses a wide alteration of the memory behaviors from no electrical bistability (NULL, co-PNI-TPA0 and co-PNI-TPA1), to static random access memory (SRAM, co-PNI-TPA2 and co-PNI-TPA5), and then to the write-once read-many times memory (WORM, co-PNI-TPA10), implying the significance of composition control on determining the memory characteristics. Mechanisms associated with the switching effect and the charge transfer in the co-PNIs were analyzed based on the optical, electrochemical results and the B3LYP/6–31G(d) calculations. The conversion of the memory effect from NULL, to volatile SRAM, and then to nonvolatile WORM is suggested to result from the gradually increased ability of the synthesized co-PNIs to form stable charge transfer complexes with the increased electron-donating DATPA species. The fine memory tuning achieved here reveals the particular availability of the copolymerization strategy in designing functional polyimides with controlled performances for practical memory applications.

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