The Effects of Sb and B Doping on the Conductive Properties of Tin Dioxide (Part B)

Abstract

<p> This report deals with the effects of various parameters on the resistance and the temperature coefficient of resistance (or the T.C.) of tin dioxide films doped with antimony and boron. The films were produced on cylindrical ceramic substrates by the hydrolysis of SnCl4 and SbCls in the presence of HCl and H3BO3. The T.C. was measured over the range of 25 to 150°C and averaged.</p> <p> Under normal conditions, the films were produced at 950°C with an antimony concentration of 0.457 molar % and a boron concentration of 2.73 molar %. Varying this firing temperature (from 800-1100°C) was found to have no effect on the resistance but increased the T.C. by 2 to 3 ppm/°C per degree change. Varying the antimony content from 0 to about 1 molar % was found to have little effect on resistance. The effect on T.C. was to increase it at lower Sb levels and then to decrease the T.C. as the level increased.</p> <p> Varying the boron content (0 to 4.46 molar %) was also found to have little effect on resistance. A decrease in T.C. with boron content was noted when only the boron was varied, but an increase in T.C. was found when HCl and H2O volumes were varied with the boron. The introduction of additional air into the system was found to have no effect.</p> <p> Film thicknesses were varied by controlling the chemical flowrates. Thinner films were found to have dramatically higher resistances and reduced T.C. values. It was observed that below a certain flowrate resistive failure occurred in the films. It was found in this study that within the statistical distribution of film values, those samples with above average resistance had below average T.C. values and vice-versa. Annealing in vacuum at 500°C was found to produce samples of reduced resistance and increased T.C. while the opposite was found with air annealed samples. Quickly cooled samples were found to be more stable.</p>