Fabrication of Thin Film Multijunction Thermal Converters With Improved Long-Term Stability

To increase the long-term stability of thin-film multijunction thermal converters (TFMJTCs) developed by the National Metrology Institute of Japan and Nikkohm Corporation Ltd., we prevented their degradation by improving the design and fabrication process. Judging from the Arrhenius model experiments, we successfully increased the lifetime of a renewed TFMJTC to more than 20 years by improving the deposition pattern of a Bi-Sb-Cu-based thin-film thermopile. We also evaluated the thermoelectric effect of the renewed TFMJTCs by the fast-reversed dc method. The low thermoelectric effect of less than 0.1 μV/V has been realized, which is comparable with that of high-quality multijunction thermal converters previously produced by other national metrology institutes.