Tuning electrical memory properties by varying terminal moieties of functional hyperbranched polyimides

摘要

In this paper, three functional hyperbranched polyimides (HBPIs) terminated with N-(4-aminophenyl) carbazole (APC), 4-aminotriphenylamine (ATPA) and N-(4-aminophenyl) phenoxazine (APP) were synthesized and denoted as 6FDA-HBPI-APC, 6FDA-HBPI-ATPA and 6FDA-HBPI-APP. In these polymers, 4, 4'-(hexa-fluoroisopropylidene) diphthalic anhydride (6FDA) served as electron-acceptor and the terminal moieties served as electron-donor to promote charge-transfer (CT). The difference among the three terminal moieties was the different links between the two benzene rings in the triphenylamine moiety for the APC (C-C single bond), ATPA (ether bond) and APP (without chemical bond), respectively. This structure variation can lead to different electron-donating abilities of the terminal moieties. Memory devices using HBPI films as building blocks with sandwich structure of indium tin oxide (ITO)/HBPI/Al were fabricated to evaluate the performance of the polymers. Current-voltages (I-V) characterization results suggested that all the devices exhibited volatile static random access memory (SRAM) behavior as well as excellent stability under constant voltage during operation time. The orbital levels obtained from the UV-vis and cyclic voltammetry (CV) measurements show the same change trend as that calculated by molecular simulation. The gradually increased HOMOs indicated the enhanced electron-donating ability of APC, ATPA and APP, resulting the decreased threshold voltages.