Investigation Into Surface Potential Decay of Polyimide by Unipolar Charge Transport Model

To predict spacecraft charging levels and mitigate electrostatic discharges, it is very important to understand the charge transport properties of highly insulating materials such as polyimide. The combination of surface potential decay (SPD) experiment and unipolar charge transport (UCT) model investigates the charge transport properties of polymide. In a simulated space environment chamber, the SPD experiments are performed on polymide. After irradiated by electron beams, the surface potential distributions of the sample are measured by a noncontact potential probe (Trek). The UCT model that consists of relaxation polarization, charge injection, charge migration, charge trapping, and detrapping processes simulates the SPD results. In the numerical UCT model, we solve the charge continuity equation by Runge-Kutta discontinuous Galerkin method and Poisson´s equation by boundary element method. The least square error between the experimental and the simulated SPD results is searched by genetic algorithm (GA). From the GA calculation, we optimize the charge transport parameters of polyimide. Then, we calculate the space charge evolution properties during the SPD process of polyimide by the UCT model. These charge transport parameters, then, can be used to study the surface charging or deep dielectric charging of the insulator.