Magnetoresistive thick film sensor for linear displacements

A new thick film material has been developed starting from Ni and Co powders in the ratio Ni:Co = 3:1. The thermal treatment (in N₂, up to 950 °C) of the metal films deposited on glazed alumina enables the in situ formation of the NiCo alloy. The films as created exhibit a high longitudinal (current I parallel to the field B) magnetoresistive response with ΔR/R ≈4% at 1.2 kGauss, and a negligible transverse one. The temperature coefficient of resistance (TCR) is ≈2700 ppm °C⁻¹. These properties make the new material superior, from the point of view of magnetoresistive applications, to the Ni-based currently available thick film conductors. Contactless sensors for linear displacements have been created with the sensor's structure enclosing either Ni-based and Ni/Co-based meanders, having two magnetoresistive elements on each side of the substrate. This paper compares the magnetoresistive and thermoresistive properties of Ni and Ni/Co-based layers as well as the performances of the sensors in the range −20 to 120 °C.