**5. Charge accumulation behavior in the PI (polyimide) bulk under high temperature (100–150 °C)**

Currently, polyimide is demanded for using an insulating material for power electric devices using SiC(silicon carbide) is required [2]. As it is developed enough to be used at high temperature under high electric stress, the insulating materials supporting the device must also exhibit extremely excellent insulation properties at high temperatures under high electric stresses.

In recent years, evaluation methods using storage characteristics of space charge has been as an effective technique to evaluate the character is tics under high electric stress. Under the stress, the current-electric field characteristic often deviates from the Ohm's law and the reason of it is considered that the space charge accumulates in the material [1, 3, 5]. Therefore, if the space charge accumulation state becomes clear, the insulation performance of the material under a high electric field can be evaluated.

Recently our laboratory, has P(VDF/TrFE) (vinylidene fluoride/ ethylene trifluoride copolymer), has been used as a piezoelectric sensor that can be measured even under high temperature, and we can obtaine the space charge distribution in the insulating materials even at relatively high temperatures of up to 150 °C using the developed apparatus. In this report, we introduce some typical measurement results of the space charge accumulation behaviors in the polyimide (PI) obtained using the developed system.
