Influence of microstructural variation on the electrical properties of SiC microthermistors

The effects of the microstructural nonuniformity on the variations in the electrical properties of SiC ceramic were estimated quantitatively through simulations in order to produce microthermistors with the material. In these simulations, the grain size, the trap concentration at the grain boundary and the doping level in the grain were considered as the various microstructural nonuniformities. The device size was also taken into account as a parameter. The boundary potential model and the energy band model were used to express the electrical characteristics of the grain boundaries in the simulations. It is pointed out that those nonuniform microstructures greatly influence the electrical conductivity and the sensitivity of the SiC ceramic microthermistor. These phenomena are explained by the percolation theory. The tolerance of microstructural variation in the production of the ceramic is also discussed. It is revealed that the percolation threshold has the possibility to be used as an index of the acceptable microstructural tolerances.