High Performance Volatile Polymeric Memory Devices Based on Novel Triphenylamine-based Polyimides Containing Mono- or Dual-Mediated Phenoxy Linkages

Two novel functional polyimides (PIs), PI(AAPT-TPA) and PI(APT-TPA), consisting of electron-donating 4-amino-4'-(p-aminophenoxy)-triphenlamine (AAPT) or 4,4'-bis(p-aminophenoxy)-trophenylamine (APT) and electron-accepting phthalimide moieties, were prepared for the memory device applications. The TPA moietics as electron donor are expected to enhance the electron donating and charge transport ability with phthalimide moieties (electron acceptor). The monophenoxy linkage PI(AAPT-TPA) had a higher T-g and a lower band gap than the dual-phenoxy lindage PI(APT-TPA). It suggested the more rigid backbone of the former and led to different memory characteristics. The memory devices with the configuration of ITO/PI/Al exhibited two conductivity states and could be swept positively or negatively with a high ON/OFF current ratio of 10(8)-10(9). The PI(AAPT-6FDA) device relaxed from the ON state to the OFF state quickly after the applied voltages was removed, wheras teh ON state of the PI(APT-6FDA) device could remain for around 4 min after the power was turned off. It suggested that dynamic random access memory (DRAM) was exhibited for the PI(AAPT-6FDA) device and that static random access memory (SRAM) was for the PI(APT-6FDA) device. The volatile memory characteristics were probably attributed to the unstable charge transfer (CT) complex based on the weak theoretical dipole moments of the studies PIs. The dual-mediated phenoxy linkage of PI(APT-6FDA) led to the more twisted conformation compared to the monosubstitued PI(AAPT-6FDA) based on the theoretical analysis by the density functional theory (DFT) method. It thus produced a potential barrier for delaying the back CT process by the electric field and explained the SRAM characteristic. The present study suggested the importance of the TPA structure for the memory characteristics. The fast switching and high ON/OFF characteristics also indicated the new TPA based polyimides for advanced memory technology.