A Study of the Elastic Constants of 4H Silicon Carbide (4H-SiC)

Stress sensors integrated on silicon ICs represent a powerful tool for experimental evaluation of die stress distributions, but silicon's upper temperature range is limited by its relatively low bandgap energy. Stress sensors made with wide bandgap semiconductor such as 4H silicon carbide (4H-SiC) offer the advantage of much higher temperature operation and can be utilized to monitor stresses in high-voltage, high-power SiC devices and have applications in deep well drilling, geothermal plants, and automotive and aerospace systems, to name a few. Strain distributions can be evaluated from stresses according to single crystal elastic constants [Cij]. However, elastic properties of 4H-SiC evaluated by several groups using various methods have relatively large variations. Therefore, determining the elastic constants of 4H-SiC carbide is essential for improving measurement accuracy. This paper discusses the theory and extraction of elastic constants of 4H-SiC. Coordinate transformations of engineering strain, tensorial strain, stress and stiffness matrices are reviewed here. Experimentally, the elastic properties of 4H-SiC are measured using both nano-indentation and fourpoint bending beam deflection methods. Strain gauges were also used for validation of elastic modulus and measurement of the Poisson's ratio. The elastic stiffness coefficients for 4HSiC available in the literature were compared with our data.