Processing of Novel Strontium Titanate-Based Thin-Film Varistors by Chemical Solution Deposition

Strontium titanate (SrTiO₃)-based multilayered film with varistor characteristics has successfully been fabricated by a chemical solution deposition (CSD) method. Homogeneous precursor solutions of SrTiO₃ and Nb:SrTiO₃ with long-term stability could be prepared by optimizing the reaction conditions among strontium ethoxide, titanium isopropoxide, and niobium ethoxide. Films were prepared using the precursor solutions on fused silica substrates at 700°C. Triple layered films with SrTiO₃/Nb:SrTiO₃/SrTiO₃ structure were also successfully crystallized on Pt/Ti/SiO₂/Si substrates at 700°C. The current–voltage ( I - V ) curve of the multilayered film was characteristic to varistors and the nonlinear coefficient α of the synthesized film was ∼3.0. The varistor voltages ( E _0.01) of 0.6-μm-thick film were 140 kV/cm for the forward direction and −120 kV/cm for the reverse direction, respectively, at room temperature.