Side chains contributions to characteristics of resistive memory based on water-soluble polyfluorenes: Effects of structure and length of side pendant group

This paper investigates the effects of side chains, which are important structural constituents, on the characteristics of organic resistive memory devices with water-soluble polyfluorene (WPF) derivatives. The WPF derivatives have either an ethylene oxide (EO) or an alkyl side chain the lengths of the EO side chains are 2, 4, or 6 molecules. WPFs exhibit typical bipolar switching behaviors with reliable non-volatile characteristics and good device-to-device uniformity under ambient conditions. WPFs with the EO side chains showed better memory characteristics than those of the alkyl side chains of similar length. In addition, as the EO unit lengthened, the ON/OFF ratio of the memory device gradually increased from 5 × 10² to 10⁵, and the threshold voltage (V_th) progressively decreased from 4 to 3.5 V. The retention times for WPF-hexyl, WPF-2O, WPF-4O, and WPF-6O are 10⁴, 200, 10⁴, and 10⁴ s, respectively. The excellent switching properties of WPF-4O and WPF-6O are believed to be mainly attributed to highly localized current pathways and the low trap density.