Performance Enhancement of ZnO-Based Multilayer Varistor by Constrained Sintering

The performance of a ZnO‐based multilayer varistor is affected strongly by the homogeneity of its microstructure. In this study, a homogeneous microstructure of a ZnO‐based multilayer varistor is attained by using constrained sintering, when nonreactive borosilicate glass +90 wt% alumina (Al2O3) was used as the constraining layer laminated on both sides of the multilayer ZnO‐based multilayer varistor (MLV). The mean grain size and the distribution of grain size of a ZnO‐based MLV fired by constrained sintering are both reduced, because an in‐plane tensile stress results from constrained sintering in the x–y plane of the multilayer device, which could modify the densification rate of the ZnO‐based MLV materials. The leakage current and nonlinear coefficient (α) of ZnO‐based MLVs can be greatly improved due to the inhibition of ZnO grain growth when constrained sintering was used instead of free sintering. Note that the energy absorption capabilities in terms of peak current (PC) measurements of ZnO‐based MLVs fired by constrained sintering are remarkably improved due to a homogeneous microstructure.