Sol–gel MgO thin films for insulation on SiC

Abstract

Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, high-power, and high-temperature devices from DC to microwave frequencies. However, the marketing of advanced SiC power devices remains limited due to performance limitation of the SiO 2 dielectric among other issues. Indeed, SiO 2 has a dielectric constant 2.5 times lower than SiC, which means that at critical field for breakdown in SiC, the electric field in the adjoining SiO 2 becomes too high for reliable operation. This suppresses the main advantage of using SiC power devices if the ten times higher breakdown field for SiC in comparison to Si cannot be exploited. Therefore, alternative dielectrics having a dielectric constant higher or in the same order as SiC ( ε r ≈ 10 ) should be used to reduce the electrical field in the insulator. Among alternative dielectrics to silicon dioxide (SiO 2), magnesium oxide (MgO) seems to be a good candidate regarding its bulk properties: large bandgap, high thermal conductivity and stability, and a suitable dielectric constant ( ε r ≈ 10 ). In order to evaluate such a promising candidate, the sol–gel process appears to be a convenient route to elaborate this kind of coatings. By selecting an appropriate precursor solution and optimizing the curing conditions of the films, MgO films could be obtained under various crystallization states: non-oriented or preferred [1 1 1] orientation. MIM structures have been used to investigate the insulating properties of the sol–gel MgO films. The dielectric strength of the films was found to be microstructure–dependent, and reached 3 to 8 MV/cm at room temperature. Leakage currents were measured from 150 up to 250 °C, with values less than 10 −5 A/cm 2 at 1 MV/cm.