Electrical properties of polyimide

This study examined the dielectric characteristics and conduction current characteristics of polyimide (PI) film in a wide temperature range from the room temperature to 500 degrees C using electron beam irradiated specimens. At frequency of 100 Hz, relative dielectric constant (epsilon(r)) began increasing rapidly at about 420 degrees C. The higher the dose, the smaller epsilon(r). At 10 kHz, the temperature at which epsilon(r) began increasing rapidly was higher and the value of epsilon(r) was smaller. The 100 MGy specimens had the smallest dielectric tangent (tan delta) at both 100 Hz and 10 kKz. At 10 kHz, the temperature at which, tan delta began increasing rapidly was higher than at 100 Hz. The unirradiated specimens have smaller conduction current than the irradiated specimens up to 250 degrees C, but the unirradiated specimens have larger conduction current than the 100 MGy irradiated specimens at 250 degrees C and higher. At 500 degrees C, the unirradiated specimen became equal to the 5 MGy and 50 MGy specimens. Then the space charge distribution in the specimens was measured by the PEA method. Both the unirradiated specimens and the 100 MGy irradiated specimens showed small polarization charge due to pulse application, but no charge distribution over 0.7 C/m(3) was found. From these results, it was found that the crosslinking effect began to appear at 270 degrees C and higher. However, it is suspected that the effect of carrier increase due to electron beam irradiation appeared in the temperature range below 270 degrees C, and then no local space charge in the irradiated specimen was formed.