High performance Bi–Co–Mn–Si–B-doped ZnO varistors with wide ranging breakdown voltage and high resistance to electrical degradation

A simple ZnO varistor with high resistance to electrical degradation and an adjustable breakdown voltage range of 100–3000 V/mm was developed by adding SiO₂ and B₂O₃ to Bi–Mn–Co-doped ZnO. Samples were fabricated by sintering at 1150 ºC and doped with 0–55 mol% SiO₂ to adjust breakdown voltage. High nonlinear index and low leakage current density were confirmed with addition of SiO₂; however, severe electrical degradation occurred. Addition of 1 mol% B₂O₃ successfully improved the resistance to electrical degradation and long-term reliability, due to the formation of homogenous glass-phase Bi–B–O at grain boundaries inhibiting ion migration. A stabilized interface trap with ∼0.6 eV and 10⁻²¹ (m²) was found in samples with 1 mol% B₂O₃.