The preliminary exploration on change mechanism of Seebeck coefficient for NiCr/NiSi thin film thermocouple with different thickness

By controlling the thickness of NiCr and NiSi films, a series of NiCr/NiSi thin film thermocouples (TFTCs) were prepared by the sputtering technique. With the standard static calibration procedure for wire ther-mocouple, the temperature difference mainly happened between NiCr/NiSi compensation wires, but not between pad and hot junction of NiCr/NiSi TFTCs. The incorrect temperature difference resulted in the distorted Seebeck coefficient of NiCr/NiSi TFTCs, which was close to the standard NiCr/NiSi wire thermo-couple. Only considering the temperature difference between pad and hot junction of NiCr/NiSi TFTCs, Seebeck coefficient of NiCr/NiSi TFTCs were accurately obtained. Seebeck coefficient of NiCr/NiSi TFTCs was about similar to 10 mu V/degrees C, which was obviously lower than that of standard K type NiCr/NiSi wire thermocouple (similar to 40 mu V/degrees C). Besides, Seebeck coefficient of NiCr/NiSi TFTCs gradually increased from 7.32 to 13.36 mu V/degrees C with the increase of NiCr/NiSi film thickness from 400 to 2000 nm. NiCr and NiSi films with different thickness displayed the similar crystal structure, grain size, metal bonds structure, Ni/Cr and Ni/Si atom ratio, as well as similar surface morphology and roughness, which have little influence on Seebeck coeffi-cient of NiCr/NiSi TFTCs. With the increase of NiCr and NiSi film thickness, the sheet concentration of free electron increased gradually, which resulted in the increase of Seebeck coefficient of NiCr/NiSi TFTCs. Because of the limited thickness of NiCr and NiSi film, all Seebeck coefficient values of NiCr/NiSi TFTCs were lower than that of standard K type thermocouple. NiCr/NiSi TFTCs with small thickness NiSi film and large thickness NiCr film could display the relative higher Seebeck coefficient value. And, NiCr/NiSi TFTCs with 800 nm NiSi and 2000 nm NiCr films displayed Seebeck coefficient value of 21.30 +/- 0.69 mu V/degrees C. o (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

A series of NiCr/NiSi thin film thermocouples were prepared by controlling the thickness of NiCr and NiSi films, and it was found that the temperature difference had an influence on the Seebeck coefficient, which increased with the increase of film thickness.