Impact of Humidity and Temperature on the Electrical Properties of Silicone Gel in Power Electronic Applications

In this work, the impact of humidity and temperature on the electrical behaviour of silicone gel is evaluated. The device under test consists of two round plate electrodes with a distance of 2.6mm, which were encapsulated with industrial silicone gel. This sample was placed inside a climate chamber and a step-wise increase of humidity until 85% was applied, while the temperature was set to 85°C. Subsequently, the humidity was kept constant at 85% and the temperature was decreased in steps. To measure the capacitance CS and series resistance RS during this climatic cycle, an LCR meter was used to get measurements at 200 frequencies between 100Hz and 2MHz. For each step during the climatic cycle, the temperature, humidity and capacitance was extracted after the transient changes stabilised. Since the geometry of the sample is known, the relative permittivity is calculated from the capacitance. Then, a regression was carried out for each frequency to evaluate the impact of humidity and temperature on the relative permittivity. The experimental results were used by the TCAD and Chemistry Module of Silvaco Victory Device simulation tools for dynamic and static 2D modelling.