Trap Mechanism for Thickness Effect of Breakdown in BOPP Films for Capacitors

Film capacitors are the key components for energy storage in pulsed power system, electric power system, and aerospace equipment. The thickness reduction of dielectric film is beneficial to the increase of capacitance and the decrease of cost, but has the potential to decrease dielectric strength. Therefore, it is very important to clarify the correlation between dielectric strength of dielectric film and its thickness. A series of BOPP films with thickness ranging from 3 to 15 μm are selected. Objective to study the influence of electric field of different polarity and form on breakdown characteristics of BOPP films. The microscopic relation between the thickness and the dielectric strength of BOPP films is established by the trap energy level and distribution. The experimental results show that the breakdown field strength ceases its monotonous increase with the decrease of the thickness. The energy level and distribution of trap and the microstructure show that the defects in BOPP films are the apparent causes affecting the dielectric strength. The shallow trap and its density caused by defects are the physical mechanism of reducing dielectric strength. The calculation base on charge trapping kinetic equation also shows that the high-density shallow trap is not conducive to the trapping of free charge in BOPP films.