Space charge distribution and capacitance-voltage characteristics of metal/polyimide Langmuir-Blodgett film/metal structure

The capacitance-voltage (C-V) characteristics of the metal/polyimide (PI) Langmuir-Blodgett (LB) film/metal structure are analyzed, taking into account the interfacial electrostatic phenomena and the presence of the interfacial electronic states. The capacitance (𝒞) and the additional relative capacitance [(𝒞-𝒞₀ )/𝒞₀] at various applied external voltages (V_ex) are calculated, under the assumption that the electron acceptor density of states (DOS) at the interfaces has a Gaussian profile centered at the energy level of the lowest unoccupied molecular orbital (LUMO). The results reveal that when a positive bias (V_ex >0) is applied to a metal/insulator (PI LB film)/metal (MIM) element, the capacitance and the additional relative capacitance decrease as the thickness of PI LB film increases, while a negative bias (V_ex<0) gives rise to slight changes of the capacitance and the additional relative capacitance. In addition, it is found that the density of space charge also experiences slight changes as the applied external bias increases. The calculated results of the C-V characteristics of the MIM element show good agreement with the experimental results