Effect of metal ions on the switching performance of polyfluorene-based organic non-volatile memory devices

We investigated the switching behavior of the polyfluorene-derivatives (WPF-oxy-F) with and without metal ions (Ca²⁺ and Na⁺). Basic memory behavior (e.g., current-voltage sweep, cumulative probability and retention) was not significantly affected by the metal ions, and the materials displayed an on/off ratio of more than three orders of magnitude, as well as good device-to-device uniformity and >10⁴ s of retention time. However, the threshold voltage of Na-WPF-oxy-F containing Na⁺ was found to be lower than that of Ca-WPF-oxy-F containing Ca²⁺, due to the looser binding between the sodium ion and the ethylene oxide unit in Na-WPF-oxy-F. Both Ca-WPF-oxy-F and Na-WPF-oxy-F showed area dependence in the low resistance state, implying that localized current flow is assisted by metal ions. In addition, the response time of Ca- and Na-WPF-oxy-F was faster than that of WPF-oxy-F, suggesting possible modulation of memory performance by the addition of metal ions in the polymer layer.