Preparation And Performances Of The Tin Oxide-based Film Vsristors

As an electronic component for overvoltage protection,varistors are widely used in all kinds of electronice quipments and electric systems to suppress the high voltage as well as transient surge current in electric transmission lines.However,with the development of science and technology,new film varistors with smaller size and low varistor voltage are necessary to be developed.At present,the researches on SnO₂-based film varistors are not mature enough,because the fabrication process is complex,and the obtained sample exhibits low nonlinear coefficient as well as high varistor voltage.Therefore,in this paper,RF magnetron sputtering technology is adopted to fabricate oxygen-deficient tin oxide films,and then the films are buried in Sb₂O₃?Ta₂O₅?Nb₂O₅ powders for thermal treatment.This method not only decrease the tin oxide grain resistances,but also increase the grain bourndry resistances,leading to effective double schottky barrier,and finally series SnO_2-x-based film varistors are successful prepared.?1?Series oxygen-deficient tin oxide films were deposited by RF magnetron sputtering technology under different O₂/Ar ratios and sputtering powers,respectively.And the influence of O₂/Ar ratios and sputtering powers on the films are studied systematically.On the basis of test results,As the O₂/Ar ratio increases,the film thickness and deposition rate rises up first and then fells down,reaching the maximum value when the O₂/Ar ratio is 1:4;the grain size of tin oxide in film gradually decreases;and the O/Sn ratio of the film increases constantly.In addition,due to the decrease of carrier concentration in the film,the corresponding electrical resistivity increases sharply with the increasing O₂/Ar ratio.On the other hand,the polycrystalline tin oxide films are deposited under high sputtering powers.With the increasing sputtering power,the grain size,film thickness and deposition rate of tin oxide film all increase gradually.Furthermore,the decrease of carrier concentration leads to the increasing electrical resistivity of tin oxide films.?2?The oxygen-deficient tin oxide films prepared via RF magnetron sputtering technology are buried in Sb₂O₃ powders for thermal treatment,and the effects of hot-dipping temperature?200-600??on the phase composition,microstructure,element distribution and electrical performance of series SnO2-x-Sb2O3 film varistors are studied systematically.Based on the characterization results,it can be concluded that Sb₂O₃ diffuses into the tin oxide film during hot-dipping process,which would accumulate at tin oxide grain boundary to form a high resistance isolation layer,building effective double schottky barrier,making the sample exhibit typical nonlinear current-voltage characteristics.The sample prepared at 500?reaches the highest nonlinear coefficient value of 10.88,accompanying with the lowest leakage current value of 36.3 mA/cm²,and the breakdown electric field of 0.0188 V/nm.In addition,the bourdary barrier height of series SnO_2-x-Sb₂O₃ film varistors are calculated in this paper,which exhibit the same trend with nonlinear coefficient with increasing hot-dipping temperature.?3?The oxygen-deficient tin oxide films prepared via RF magnetron sputtering technology are buried in Ta₂O₅ powders for thermal treatment,and the effects of hot-dipping temperature?300-800??on the phase composition,microstructure,element distribution and electrical performance of series SnO_2-x-Ta₂O₅ film varistors were studied systematically.During the hot-dipping process,Ta atoms could diffuse into the tin oxide film though thermal diffusion,gathering in the form of Ta₂O₅ at the grain boundary as high-resistance isolation layer,which would build effective double schottky barrier.SnO2-x-Ta2O5 film varistor fabricated at 600?exhibits the highest nonlinear coefficient of 16.8,the lowest leakage current of 4.1mA/cm² and the breakdown electric field of 0.0313 V/nm.Furthermore,the bourdary height of series SnO_2-x-Ta₂O₅ film varistors are calculated,and in order to explain the mechanism of nonlinear behavior,a grain-boundary defect barrier model based on SnO_2-x-Ta₂O₅ film varistors is proposed.?4?The oxygen-deficient tin oxide films prepared via RF magnetron sputtering technology are buried in Nb₂O₅ powders for thermal treatment,and the effects of hot-dipping temperature?300-700??on the phase composition,microstructure,element distribution and electrical performance of series SnO_2-x-Nb₂O₅ film varistors were studied systematically.Nb atoms could enter tin oxide grain boundary through thermal diffusion,forming a high-resistance Nb2O5 isolation layer,building effective double schottky barrier at tin oxide grain bourndry.The nonlinear coefficient of the series film samples reaches the maximum value of 14.73 at hot-dipping temperature of500?,corresponging to the leakage current value of 17.1mA/cm²and the breakdown electric field of 0.0201 V/nm.Besides,as for series SnO_2-x-Nb₂O₅ film varistors,a grain-boundary defect barrier model is proposed in this paper,which is used to explain the mechanism of nonlinear nature in SnO_2-x-Nb₂O₅ film varistors.