*Polyimide for Electronic and Electrical Engineering Applications*

**Figure 7.** *Example of the depth profiles of (a) space charge and (b) internal electric field (25–125 kV/mm, positive polarity).*

distributions are deduced from Eq. (1) as shown in **Figure 7(a)** and **(b)**, respectively. In this case, positive and negative space charges are confirmed close to and at the depth of from 4 to 10 μm from top Au electrode, respectively, which causes the enhancement of positive field strengthening at 2–6 μm depth. The maximum values of these are confirmed to increase along with the applied DC field. Time evolution of maximum peaks of enhanced electric field in both polarities is shown in **Figure 8**. As mentioned so far in this subsection, the space charge and enhanced electric field characteristics in polyimide under external DC voltage on and off can be evaluated by using LIMM method including both depth-profile and time evolution.

*Behavior of Space Charge in Polyimide and the Influence on Power Semiconductor Device… DOI: http://dx.doi.org/10.5772/intechopen.92165*

**Figure 8.** *Magnitude of positive peaks of internal electric field.*

**Figure 9.** *Maximum negative space charge density.*

**Figure 10.** *Maximum positive internal electric field.*

**Figure 11.** *DC conductivity.*
