Power devices used in the automotive field are subject to critical conditions in terms of high temperature, humidity and applied voltages. This harsh environment can cause progressive reduction of their electrical performances, fast degradation and ultimately, failure. For these reasons, an optimal passivation layer (or a mix of layers) can be vital for the extension of devices' lifetime. Usually, inorganic materials like amorphous silicon or silicon nitride are widely used in microelectronics but recently also organic materials can find their application. According to the employed deposition technique, the final passivation layer's quality can change, affecting its characteristics as dielectrics. Moreover, its interaction with other active or inactive material on the substrate during several steps of the fabrication line can play an important role, ending up in a modification of its structural and electrical properties.