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) L angmuir-Blodgett (LB) film/metal structure are analyzed, taking into accoun t the interfacial electrostatic phenomena and the presence of the interfaci al electronic states. The capacitance (C) and the additional relative capac itance [(C - C-0)/C-0] at various applied external voltages (V-ex) are calc ulated, 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 orbitals (LUMO). The results reveal that when a positive bias (V-ex > 0) is applied to a metal/insulator (PI LB fil m)/metal (MIM) element, the capacitance and the additional relative capacit ance decrease as the thickness of PI LB film increases, while a negative bi as (V-ex < 0) gives rise to slight changes of the capacitance and the addit ional relative capacitance. In addition, it is found that the density of sp ace charge also experiences slight changes as the applied external bias inc reases. The calculated results of the C-V characteristics of the MIM elemen t show good agreement with the experimental results.