Development of Thin-Film Multijunction Thermal Current Converters With Increased Rated Current

Abstract

Thin-film multijunction thermal converters (MJTCs) with a heater fabricated on an AlN chip have been developed for ac–dc current transfer standards. The rated current of the MJTC can be increased due to the good thermal conductivity of the AlN substrate, which acted as a heat sink drawing away heat from the heater. The AlN chip was mounted on a polyimide foil with thermocouples of the MJTC produced separately. In the case of an MJTC with a heater resistance of 5 $\Omega$ , which has a bifilar heater pattern to reduce the thermoelectric effects, the nominal current is 200 mA. The observed current level dependence of the ac–dc current transfer differences from 50 to 200 mA for the 5- $\Omega$ MJTC was within 1 $\mu\hbox{V/V}$ at frequency from 1 to 100 kHz. Compared with a conventional thermal converter, the wide range of available input current and small current level dependence of the new MJTCs may reduce uncertainties of ac–dc current transfer standards.