Inserting phenylethynyl linker into triphenylamine-based hyperbranched polyimide for effectively tuning memory performance

Abstract

In this paper, a novel triamine monomer, tris(4-(2-(4-aminophenyl) ethynyl) phenyl) amine) (TAEPA) had been designed and synthesized through Sonogashira coupling reaction. The phenylethynyl of TAEPA was inserted as a π bridge into the D-A structure of hyperbranched polyimide (HBPI). This structure could tune the memory performance of HBPI based devices. The memory devices had been fabricated from two HBPIs, TAEPA-6FHBPI and TAP-6FHBPI, which were synthesized from TAEPA and tris-(4-aminophenyl)amine (TAPA) with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), respectively. The latter one was used as the control experiment. Current-voltages (I-V) characterization results suggested that two devices exhibited totally distinct memory behaviors. The TPA-6FHBPI based device exhibited volatile static random access memory (SRAM) behavior with a threshold voltage of −2.9 V, while the device based on TAEPA-6FHBPI exhibited non-volatile write once read many-times (WORM) behavior with a lowered threshold voltage of −1.6 V. Both devices exhibited long-term stability with retention time of 10000 s under a constant bias of −1.00 V. The orbital degeneracy in LUMOs of HBPIs and the introduction of conjugated phenylethynyl could significantly lowered the threshold voltage of memory devices due to their synergistic effect on improving the charge transfer. In addition, the introduction of conjugated phenylethynyl could prevent the devices relaxing from the excited state to ground state and convert their memory characteristic from SRAM to WORM.