Synergistic In2O3 doping and low-temperature sintering for high-performance ZnO-Bi2O3 varistors via grain-boundary engineering

An order-of-magnitude reduction in leakage current density via 0.1 mol% In 2 O 3 doping compared to reference varistors. • Synergy of doping and low temperature sintering increased interface-state density (Ns) at grain boundaries and barrier height. • The 900 °C fired microstructure corroborates the strengthened boundary insulation, evidenced by charge distribution across grain boundaries using DPC-STEM. ZnO-based varistors protect sensitive electronics by clamping high-voltage transients closely associating with dopant chemistry and grain-boundary architecture. Here, nano-ZnO precursors coupled with 0.1% (in mole) In 2 O 3 enable low-temperature sintering and dense ZnO-Bi 2 O 3 varistors. Record-low leakage current (0.03 μA/cm 2 ), high nonlinearity ( α = 68) and elevated breakdown field (692 V/mm) are achieved simultaneously, fully compatible with Ag inner electrodes. The synergy-resulted increase in interface-state density (Ns) at grain boundaries raises the Schottky barrier height ( ϕ b ) from 0.723 eV to 0.744 eV by thickening electron depletion layer. Impedance spectroscopy reveals higher activation energy (1.02 eV), longer grain-boundary relaxation times, and higher resistivity with In 2 O 3 -doping, supporting the Double Schottky Barrier model, while in-situ DPC-STEM directly maps strengthened charge trapping across individual boundaries. The formulation fires 150 °C below industrial practice and transfers immediately to LTCC multilayer chips for miniaturized, high-performance surge protectors. Download: Download high-res image (350KB) Download: Download full-size image