Regulating the electrical bistable memory characteristics in functional polyimides by varying the spatial position of the electron-donating species

Four novel functional polyimides (PIs) for electrical memory applications, DATP6Cz-DSDA, DATP2Cz-DSDA, DATP6Cz-NTDA, and DATP2Cz-NTDA, were synthesized through condensation polymerization of two diamines, N,N-bis(4-amino)phenyl-6-(9-carbazol)-hexamine (DATP6Cz) and N,N-bis(4-amino)phenyl-2-(9-carbazol)-ethylamine (DATP2Cz), with two dianhydrides, diphenylsulfone-3,3',4,4'-tetracarboxylic dianhydride (DSDA) and 1,4,5,8-Naphthalenetetracarboxylic dianhydride (NTDA). The ethyl and hexyl spacer were intentionally inserted into the diamines to alter the spatial position of the electron donor in the PIs and then to elucidate the effect on the memory behavior. Experimental results show that DATP6Cz-DSDA and DATP2Cz-DSDA exhibit nonvolatile WORM memory behavior, while DATP6Cz-NTDA and DATP2Cz-NTDA exhibit volatile SRAM and DRAM behavior, respectively. Simulation results indicate much stronger charge-trapping effect of the sulphone moiety in DSDA than that of the carbonyl moiety in NTDA, accounting for the nonvolatile feature of the DSDA-based PI memories and the volatile feature of the NTDA-based PI memories. Meanwhile, spatial position effect was observed in the NTDA-based PIs. The spacer of varied length between carbazole group and diphenyl amino group in DATP6Cz and DATP2Cz, i.e., hexyl vs. ethyl, has significantly altered the spatial position of the electron donor and the charge transportation path in the PIs, resulting in different retention time and corresponding SRAM and DRAM behavior. The present strategy is expected to be applied in material design in future information technology.