Segmented FGM for linearization of the characteristics of /spl beta/-FeSi/sub 2/ based thermal sensors

Highly sensitive thermal sensors can be developed when replacing metallic alloys in high temperature thermoelectric (TE) detectors by semiconducting materials. Functionally graded materials (FGM) can be used to tune the temperature characteristics of the signal responsivity, which should be independent from temperature. A technique of preparing segmented TE FGM of FeSi/sub 2/ doped with Al, FeSi/sub 2/ doped with Mn, or FeSi/sub 2/ double doped with Mn and Al is demonstrated. A correlated variation of the TE properties caused by change of the doping is found. The doping content of the material was varied mainly to control the temperature dependence of the Seebeck coefficient S. For highly responsive heat flux sensors, high S and low K are desired. Al+Mn double doping was employed to achieve proper S values. The linearization of sensor characteristics needs in the easiest approach a temperature independent S. This aim was met using a stack of segments with different temperature curves of the Seebeck coefficient. Constant integral thermopower between -50/spl deg/C and +500/spl deg/C with a comparably high value of about 270 /spl mu/V/K was numerically predicted for the stack with a dispersion below 5%. Accordingly, a segmented thermocouple has been prepared after the modeling results and has been characterized.