Microstructure and Electrical Properties of Low-Voltage Barium Titanate Doped Zinc Oxide Varistor Ceramics

Abstract

In the present, varistor ceramics through the combination of zinc oxide (ZnO) with a perovskite material have become widespread because of their unique properties for a wide range of applications in electronic protection devices. Low-voltage zinc oxide (ZnO) varistors with fast response and highly nonlinear electrical properties for overvoltage protection in an integrated circuit are increasingly significant in the application of low-voltage electronics. The present study highlights the interaction between barium titanate (BaTiO3 ) and ZnO varistors through the employment of solid-state reaction method in the production of low-voltage varistors. The effects of BaTiO3 on the microstructure of ZnO varistors were analyzed through scanning electron microscopy (SEM), energy dispersive X-ray analysis spectroscopy (EDS) and X-ray diffraction (XRD). The EDS analysis and XRD measurements suggest the presence of ZnO and BaTiO3 phases. The electrical properties of BaTiO3 -doped ZnO varistors were examined based on the current density-electric field (J-E) characteristics measurement. The varistor properties showed the nonlinear coefficient (α) from 1.8 to 4.8 with the barrier height (φB) ranged from 0.70 to 0.88 eV. The used of BaTiO3 additive in ZnO varistors produced varistor voltages of 4.7 to 14.1 V/mm with the voltage per grain boundary (Vgb) was measured in the ranges 0.03 to 0.05 V. The lowest leakage current density was 348 µA/cm2 , obtained at the samples containing 12 wt.% BaTiO3 with high barrier height. The reduction in barrier height with increasing BaTiO3 content was associated with the excessive amount of BaTiO3 phase, hence cause the deterioration of active grain boundary due to the variation of oxygen (O) vacancies in the grain boundary.

Nonlinearity Characteristics of Low-Voltage Barium Titanate Based Zinc Oxide Varistor Ceramics Modified by Cobalt Dopants

“…These secondary phases are mainly located at the grain boundaries and responsible for enhancing the barrier height and reducing the ZnO varistor's leakage current. Moreover, the performance of the fabricated device was enhanced by Co 3 O 4 dopant since it showed an excellent electrical characteristic with good nonlinearity for low-voltage varistors compared to the varistor fabricated from the previous study [4,23,27].…”

“…A preliminary test of electrical characteristics on finalizing the BaTiO 3 and ZnO composition was characterized by nonlinearity measurement [23]. Table 2 shows that the highest value of the nonlinear coefficient (α) was obtained from the sample with 12 wt.% of BaTiO 3 content.…”

“…J-E characteristics parameters of ZnO varistor sample with different amounts of BaTiO3 additive[23].…”