Flexible hot-film sensor array fabricated with sputtering-electroplating micromachining

In order to measure dynamically the local temperature or wall shear stress of a flow, a new structure of flexible hot-film sensor array and its fabrication process are proposed. The thermal sensing material, nickel, is sputtered on a polymide flexible substrate, and then patterns to form both the thermal resistor array and the leads' sublayer, on which copper is electroplated and lift-off patterned to form the metal leads. Electroplating can realize economically higher thickness of the lead film than does sputtering to keep the lead resistance small and minimize its influence on thermal sensing. High temperature coefficient of resistance (TCR) is obtained over 3.6 × 10^-3/°C with nonlinearity under 0.7%. Wind tunnel experiments show that the developed sensor can measure wall shear stress with high repeatability. This flexible sensor array possesses reliable connections between the flexible thermal resistors and leads, and can be used to measure the dynamic distribution of flow parameters on non-planar surfaces.