Direct‐Write Fabrication of Zinc Oxide Varistors

Abstract

Zinc oxide (ZnO)‐based pastes with tailored rheological properties have been developed for direct‐write fabrication of thick‐film varistor elements in highly integrated, multifunctional electroceramic devices. Such pastes exhibited pseudoplastic behavior with a low shear apparent viscosity of roughly 1 × 10 4 Pa·s. Upon aging, the pastes attained printable, steady‐state viscosities of approximately 3 × 10 2 Pa·s at 10 s −1 . Square and rectangular elements were patterned on dense alumina substrates and sintered at varying temperatures between 800° and 1250°C. Varistor elements fired at 900°C exhibited nonlinearity coefficients (α= 30) that were equivalent to high‐density (>95%) varistors formed by cold isostatic pressing at 100 MPa (15 ksi) of a similar chemically derived powder heat‐treated under analogous conditions.