ZnOバリスタのSi添加の課電劣化改善への影響

Abstract

The effects of Si addition on the electrical degradation of the ZnO varistors were investigated by voltage-current (V-I ), capacitance-voltage (C-V ) methods, and Isothermal Capacitance Transient Spectroscopy (ICTS). The nonlinearity index α for the Bi-Mn-Si-added ZnO varistors didn’t show the remarkable change but that for the Bi-Co-Si-added ZnO varistors decreased by Si addition. Values of α after electrical degradation showed the local maximum at approximately 700molppm for Bi-Mn-added ZnO varistors and at approximately 500molppm for Bi-Co-added ZnO varistors. It is found that the electrical degradation can be hindered at these optimum Si contents. EC-ET showed the local maximum at the optimum Si content similar to α for the Bi-Mn-Al-added ZnO varistors but those for Bi-Co-Si-added ZnO varistors showed the local minimum at the optimum Si content contrary to α for Bi-Co-Al-added ZnO varistors. The density Nis of the interface trap levels obtained by C-V characteristics and ICTS for both kinds of ZnO varistor showed the local minimum at the optimum Si content similar to Al added Bi-Mn-added and Bi-Co-added ZnO varistors.