Modeling how defects affect conductivity of capacitor materials

Often modern electronic devices contain polycrystalline materials, in which properties are determined by both the quality of the individual crystal grains and the boundaries between them. Wu et al. developed a model to predict the interactions of two types of defects in polycrystalline materials: point defects – missing or misplaced atoms – and grain boundaries.

Bridging fundamental models of quantum mechanics with larger length scales, the authors were able to simulate both atomic level interactions and the resultant properties of electronic devices. They demonstrated their computational framework on the polycrystalline capacitor material strontium titanate.

Their model offers a bottom-up understanding of conductivity of polycrystalline materials and subsequent electrical properties of devices. They found that the grain boundaries perturb the point defects, forming what are known as space charge regions. As grain size decreases from the microscale to the nanoscale, these space charge regions begin to overlap each other, which affects the local defect chemistry, altering the defect distribution and conductivity within the material.

The handful of existing models capable of examining this behavior require significant experimentation, limiting their extension. This model does not rely on experiment, cutting costs and broadening its potential applications.

“Our computational framework can be extended to new materials and can readily switch from one material to the next,” said author Douglas Irving. Next, the authors will use the model to study other materials relevant to the capacitor industry, such as barium titanate, as well as different dopants.

Source: “Influence of space charge on the conductivity of nanocrystalline SrTiO₃,” by Yifeng Wu, Preston C. Bowes, Jonathon N. Baker, and Douglas L. Irving, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0008020 .