New Donor-Acceptor Random Copolymers with Pendent Triphenylamine and 1,3,4-Oxadiazole for High-Performance Memory Device Applications

We report the synthesis and resistive-type switching memory characteristics based on new P(VTPA(x)BOXD(y)) and P(CNVTPA(x)BOXD(y)) random copolymers containing different donor/acceptor ratios (8/2, 5/5, and 2/8) of pendent electron-donating 4-vinyltriphenylamine (VTPA) or 4,4'-dicyano-4 ''-vinyltriphenylainine (CNVTPA) and electron-withdrawing 2-(4-vinylbiphenyl)-5-(4-phenyl)-1,3,4-oxadiazole (BOXD). The effects of donor/acceptor ratios and cyano side group on the memory characteristics were explored and compared with properties of homopolymers, PVTPA, PCNVTPA, and PDXD. The distinct electrical current-voltage (I-V) characteristics of the ITO/P(VTPA(x)BOXD(y))/Al device changed from volatile memory to insulator depending on the relative donor/acceptor ratios. The ITO/P(VTPA(8)BOXD(2)) or PVTPA/Al device exhibited SRAM or DRAM behavior with an ON/OFF current ratio of 10(7)-10(8). However, no switching phenomena were observed for a higher BOXD ratio. Moreover, the devices could endure 10(8) cycles under a voltage pulse and show a long retention time for at least 10(4) s under constant voltage stress. The low-lying HOMO energy level of BOXD was employed as the hole-blocking moiety as the charge transport occurred between the neighboring triphenylamine units. The charge trapping/spontaneously back-transferring of trapped carriers controlled the switching behavior. On the other hand, all the P(CNVTPA(x)BOXD(y)) memory devices exhibited nonvolatile nature with NDR behavior due to the preferred interaction of Al atoms with the cyano group. Here, the results demonstrated that the pendent polymers with specific donor-acceptor chromophores could tune the memory switching characteristics for advanced electronic device applications.