Synthesis and Resistive Switching Performance of Benzothiazole-Based D-A Type Conjugated Polymer

A novel benzothiadiazole-based donor-acceptor type polymer, resistive random access memory (RRAM) material, poly4,4'-(2,7-diphenyl-9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline)-alt-4,7-bis(4-dodecyl-5-vinylthiophen-2-yl)benzoc1,2,5 thiadiazole (PFVT) was synthesized. By using PFVT as the active layer, the as-fabricated electronic device with a configuration of Al/PFVT/ITO (ITO: indium tin oxides) exhibites a nonvolatile RRAM performance. During 50 consecutive cycle-to-cycle measurements, the observed average switch-on voltage, switch-off voltage and ON/OFF current ratio are (−0.54 ± 0.01) V, (2.42 ± 0.05) V, and 1.5×10³, respectively. The cycle-to-cycle variation for the programming voltage is less than 2.1%, suggesting excellent reliability. After thermal annealing at 200 ℃, the switch-on and switch-off voltages decrease to (−0.49±0.01) V and (2.27±0.02) V, respectively, due to the enhanced material crystallinity. The switching mechanism can be assigned to the intramolecular charge-transfer occurred in the materials system. The ON and OFF-state currents can be fitted by the Ohmic current model and space-charge-limited current model, respectively. The switch-on voltage is highly associated with the bandgap of the materials. For comparison purpose, 4,4′-(2,7-diphenyl-9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline) was replaced with phenyl group to synthesize poly4-(4-dodecyl-5-((E)-4-methylstyryl)thiophen-2-yl)-7-(4-dodecyl-5-((E)-prop-1-en-1-yl)thiophen-2-yl)benzoc1,2,5thiadiazole(PPVT). In contrast to PFVT, PPVT also shows the similar RRAM performance, with a bigger switch-on voltage and a smaller ON/OFF current ratio. Replacement of bulky fluorene unit with phenyl unit leads to a sharp decrease in the thermal stability of the material and an increase in the bandgap.