Resistive-Switching Dynamics in Poly(3-hexylthiophene-2,5-diyl) Thin Films under Perforated Bottom Electrode

Abstract: The effect on the resistive switching (RS) mechanism in organic semiconductor (OSC), Poly(3-hexylthiophene-2,5-diyl) (P3HT), due to the presence of the perforated bottom electrode (PBE) is investigated. The simulation shows a high local electric field at the edges of a patterned bottom electrode (BE), which can increase the probability of metal filament formation due to high current density, suggesting that the use of a PBE can assist the RS mechanism. RS involves switching from the high resistive state (HRS) to the low resistive state (LRS) known as the "SET" process at higher positive bias, and returning to HRS from LRS is known as the "RESET" process, which can be achieved at a negative bias. Various switching mechanisms are segregated from each other by the obtained current response to applied voltage. RS due to the formation of complete metal filaments between the top and bottom electrodes showed Ohm's law behaviour. On the other hand, a slope of approximately 2 in the log-log plot signifies that the space charge limited current (SCLC) dominates the device, and hence RS comes from incomplete metal filament formation or some changes in the P3HT polymer itself. Similarly, high current density can transform the molecular arrangement from crystalline to an amorphous state due to joule heating, which leads to an intermediate OFF state. The high current density joule heating RS are from HRS to LRS, which is opposite to the metal filament based RS, hence it is called an inverted RS. The optical images of the fresh device and after multiple cycles indicate the metal percolation inside the OSC responsible for the RS. EDX spectrum at LRS in a cross-sectional transmission electron microscope (TEM) confirms the top metal percolation through the OSC and touches the BE. Therefore, the metal filament formation is the fundamental reason for these observed switching behaviours in P3HT.