Charge transport properties of dielectrics revealed by isothermal surface potential decay

Revealing the charge transport properties of space grade high insulation materials can benefit the mitigation of electrostatic discharges (ESD) on spacecraft. The charge transport properties of polyimide are investigated by an isothermal surface potential decay (ISPD) experiment under a simulated space environment chamber. After irradiated the sample by an electron gun, the 2-D surface potential distributions are measured by a non-contact potential probe. From the surface potential decay curves, we obtain current density at steady state ISPD. Analyzing the steady state current density against surface potential, we find two regimes. One is Ohmic regime and another is Space Charge Limited Current (SCLC) regime, which are separated at around -950 V with the sample thickness of 27 μm at 298 K. Ohmic resistivity and effective charge carrier mobility are calculated from these two regimes, respectively. In addition, the trap density of polyimide is derived from the SCLC theory, when the sample is charged to high initial surface potential.