An efficient and readily available novel asymmetric diamine monomer containing a strongly electron-donating triphenylamine moiety and a flexibility segment was designed and synthesized through a Suzuki coupling reaction. Then, two thermally stable and highly soluble polyimides (PI(TPA-PMDA) and PI(TPA-BPDA)) were prepared and characterized. The ITO/PI(TPA-PMDA)/Al memory device exhibited write-once read-many-times (WORM) memory behavior with a threshold voltage of −1.12 V, while the PI(TPA-BPDA) memory device demonstrated flash-type memory behavior with a turn-on voltage at −0.78 V and a turn-off voltage at +1.98 V. Both devices showed high ON/OFF current ratios beyond 103 and long retention times of 4 × 103 s. Space-charge limited-current (SCLC) conduction and local filament conduction governed the OFF- and ON-state current conduction of the two memory devices, respectively. The electrical memory switching behaviors were induced by a charge transfer process under an applied electric field, and the differences between the dihedral angles and dipole moments resulted in different memory types.
