Synthesis of polyimides containing triphenylamine-substituted triazole moieties for polymer memory applications

A series of thermally stable aromatic polyimides containing triphenylamine-substituted triazole moieties (AZTA-PI)s were prepared and characterized. The glass transition temperatures (T_g) of the polyimides were found to be in the range of 262-314 °C. The polyimides obtained by chemical imidization had inherent viscosities of 0.25-0.44 dL g ^-1 in N-methyl-2-pyrrolidinone. The number average molecular weights (M_n) and weight average molecular weights (M_w) were 1.9-3.2 × 10⁴ and 3.2-5.6 × 10⁴, respectively, and the polydispersity indices (PDI = M_w/M_n) were in the range of 1.70-1.78. A resistive switching device was constructed from the 4,4'-hexafluoroisopropylidenediphthalic dianhydride-based soluble polyimide (AZTA-PIa) in a sandwich structure of indium-tin oxide/polymer/Al. The as-fabricated device can be switched from the initial low-conductivity (OFF) state to the high-conductivity (ON) state at a switching threshold voltage of 2.5 V under either positive or negative electrical sweep, with an ON/OFF state current ratio in the order of 10⁵ at -1 V. The device is able to remain in the ON state even after turning off the power or under a reverse bias. The nonvolatile and nonrewritable natures of the ON state indicate that the device is a write-once read-many times (WORM) memory.