Influence of voltage polarity on space charge behavior in multilayered polyimide films

We investigated the relationship between the space charge accumulation characteristics and the breakdown in a single layer and double layered polyimide films under dc stress using the pulsed electro acoustic (PEA) method. In recent years, there are many examples of multilayered polyimide film is used as the flexible Printed-Circuit Board (PCB) inside an advanced electronic devices. Therefore, it is important to investigate the insulation performance of the multilayered polyimide film. In previous work, it was revealed that a space charge accumulated in a polyimide film under a high stress and it was closely relevant to the electrical breakdown. Therefore, it is also necessary to investigate the space charge accumulation characteristics of the multilayered type sample. Furthermore, we measured the space charge accumulation in various combinations of the multilayered samples under dc high electric field at 80 °C using the PEA method. From the space charge measurement, we found that the multilayered sample had more superior insulating properties than the single layer sample and the breakdown strength was improved by arranging a thin layer putting next to the anode electrode. In this paper, we investigated the influence of the combinations with the various thickness of the layers and the polarities of the contacting electrodes on the space charge behavior. As the results, we found that the space charge accumulation and the breakdown in polyimide films under dc high stress was strongly affected by the polarity of the electrode.