FILM THICKNESS INFLUENCES ON THE THERMOELECTRIC PROPERTIES OF NiCr/NiSi THIN FILM THERMOCOUPLES

NiCr/NiSi thin film thermocouples (TFTCs) with a multi-layer structure were fabricated on Ni-based superalloy substrates (95 mm x 35 mm x 2 mm) by magnetron sputtering and electron beam evaporation. The five-layer structure is composed of NiCrAlY buffer layer (2 mu m), thermally grown Al2O3 bond layer (200 nm), Al2O3 insulating layer (10 mu m), NiCr/NiSi TFTCs (1 mu m), and Al2O3 protective layer (500 nm). Influences of thermocouple layer thickness on thermoelectric properties were investigated. Seebeck coefficient of the samples with the increase in thermocouple layer thickness from 0.5 mu m to 1 mu m increased from 27.8 mu V/degrees C to 33.8 mu V/degrees C, but exhibited almost no change with further increase in thermocouple layer thickness from 1 mu m to 2 mu m. Dependence on temperature of the thermal electromotive force of the samples almost followed standard thermocouple characteristic curves when the thickness of the thermocouple layer was 1 mu m and 2 mu m. Sensitive coefficient K of the samples increased greatly with the increase in thickness of the thermocouple layer from 0.5 mu m to 1 mu m, but decreased insignificantly with the increase in thermocouple layer thickness from 1 mu m to 2 mu m, and continuously decreased with the increase in temperature. The sensitive coefficient and the stability of NiCr/NiSi TFTCs were both improved after annealing at 600 degrees C.