Development of Thin-Film Multijunction Thermal Converters With a Novel Structure

A new type of thin-film multijunction thermal converter (MJTC), which can be fabricated using a simple process, has been developed for use as high-frequency ac-dc transfer standards. The design of this MJTC reduces the coupling between a heater structure and thermocouples at high frequencies, and enables its characteristics to be calculable from the shape of the thermal converter (TC). The influence of the electromagnetic coupling between the heater and the thermocouples can be reduced to less than 20 μV/V at 100 MHz by improving the structure of the thermocouples. The nominal input current is increased to 50 mA by sputtering a heater on an aluminum nitride (AlN) substrate featuring good thermal conductivity, enabling direct comparison measurements between TCs with input resistances of 50 Ω and 1 k Ω. The frequency characteristics of our MJTCs are in a good agreement with the calculated results in the frequency range between 1 and 100 MHz. This paper describes the unique structure of the new MJTC and its frequency characteristics in the frequency range of 1-100 MHz.