**4. Effect of space charge on semiconductor devices**

As described in Section 1, the degradation (increase) of leakage current of the device is caused possibly by the formation of space charge on the surface at

### **Figure 12.**

*Peak value of internal electric field linked to field strengthening (filled circle) and enhancement ratio of those peaks (open square) versus applied electric field.*

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

semiconductor edge termination area. **Figure 12** shows that the electric field enhancement ratio defined in Eq. (2) confirmed in the LIMM measurement depending on the applied DC field of from �25 to 25 kV/mm. It is confirmed that the enhancement ratio in PI film is negligibly small (less than 1.1) for applied fields less than 10 kV/mm. However, it can reach much higher like 1.4 at higher applied field like 25 kV/mm.

$$\text{Enhanement ratio} = \frac{\text{Applied electric field} + \text{Measured electric field}}{\text{Applied electric field}} \tag{2}$$

This result implies that electric field at edge termination area should be carefully designed under such an operational electric field as is the case of SiC devices to prevent the influence of space charge accumulation. It should be noted that not only inside polyimide, but also space charge accumulations in encapsulation material and the interface between polyimide and encapsulation as its structure shown in **Figure 1** are also needed to be clarified. Moreover, the influence of environmental conditions such as temperature and humidity on the space charge behavior should be taken into account.
