Development of thin film range resistors for high-voltage AC-DC transfer standards

New thin-film range resistors have been developed at the National Metrology Institute of Japan (NMIJ) to reduce the voltage dependence of AC-DC transfer differences that have appeared in the processes of the step-up procedures over 300 V. The occurrence of voltage dependence is partly due to rising ambience temperature that may cause changes in the resistance of the resistor and the temperature dependence of the dielectric losses in the coating of the resistor. In order to avoid these problems, our new thin film heaters were directly sputtered on an AlN substrate and covered with SiO₂ film. The material of the heater is a NiCrFeAl alloy, which has a low temperature coefficient of the resistor around room temperature. This paper describes the reduction of the voltage dependence of AC-DC transfer differences over 300 V by improving the design of the range resistors for high-voltage thermal voltage converters (TVCs).