Electrical breakdown of polyimide prepared by vapor deposition polymerization

Electrical breakdown of PI (polyimide) films of thickness around 1 μm prepared by vapor decomposition polymerization (VDP film) is investigated, and the results are compared with those for films prepared by conventional solution condensation (S film). It is shown that the breakdown characteristics of VDP films in the thickness range of the order of a micron can be divided into two temperature regions. In the high-temperature region the avalanche process seems to be more probable than the thermal process, although the latter cannot be precluded. For film thickness of 1.5 μm, the S-film has a higher value of electric strength than the VDP film. This is considered to be due to the difference in molecular alignment. The electric strength for the present samples of about 1 μm is lower than those for commercial thicker films, being also associated with molecular orientation