Research on the electrical conduction characteristic of polyimide/Al2O3 nanocomposite films with low threshold field

Polyimide/Al2O3 (PI/Al2O3) composite films with different doping concentrations were fabricated by in-situ polymerization. Based on the SEM images of surface and fracture for PI composite films, it shows that the Al2O3 nanoparticles were well dispersed in the PI matrix. The electrical conduction characteristic was carefully investigated via current-voltage characteristics, photo-stimulated discharge and isothermal discharge current, respectively. The experimental results show that a remarkable nonlinear electrical conduction characteristic of PI/Al2O3 composites was observed under external electric field. The conduction current density of composites was increased by doping Al2O3 nanoparticles, while the threshold for the accumulation of space charge is reduced distinctly. The trap energy level density of PI composites doped 4 wt% Al2O3 nanoparticles (~ 8.85 × 1020/eV·m3) was higher than that of pure PI (~ 4.6 × 1020/eV·m3). Furthermore, the trapped charge layer was formed because a large number of shallow traps were introduced into PI matrix, which results in the change of electrical conduction characteristic. Besides, the appearance of trapped charge layer also leads to the improvement of corona-resistance property for PI nanocomposite films.