Doped β-FeSi2 as thin film thermoelement sensor material

For medium and high temperatures thin films of the silicide compound β-FeSi₂ may be used as thermopile material due to its high thermopower and thermal stability. From measurements of co-evaporated films conclusions have been drawn about an optimal film composition characterized by the Fe/Si ratio and the doping level. These results were the basis for the sputter deposition of p-type and n-type β-FeSi_2+x films from a composite target. Co and Ni as well as Mn and Al were used for n- and p-doping, respectively. In-situ measurements of resistivity and thermopower in the temperature range 100 K⩽T⩽970 K have been carried out. In combination with XRD experiments correlations were derived between the thermoelectric properties and the phase formation process. The β-FeSi₂ films were tested in thermopile structures with leg widths between 100 μm and 800 μm prepared by means of photolithographic patterning. Two types of thermocouples have been considered: p-type||n-type β-FeSi_2.0 and n-type β-FeSi_2.0||p-type Ni-Cr