Development, fabrication, and test of a modular eddy current micro sensor on a flexible polymer foil

This paper describes the development and fabrication of a modular eddy current micro sensor on a flexible polymer foil. Due to handling purposes during the micro sensor fabrication process the modular eddy current micro sensors are fabricated on a temporary Si substrate. To enable a release of the micro sensors at the end of the fabrication process, initial investigations concentrated on the proof of principle applying a deep reactive-ion etching (DRIE) process to structure the Si wafer. The DRIE process was used to structure Si frames, which serve as carriers for the modular micro sensors. For the evaluation of the fabricated eddy current micro sensors, electrical resistance measurements were accomplished with the integrated anisotropic magneto-resistance (AMR) sensor. The aim of these investigations was to evaluate the influence of the substrate material on the characteristics of the AMR sensor. The electrical output signal of these micro sensors were subsequently compared to electrical resistance measurements of identical AMR sensors fabricated on a Si substrate and served as reference. To prove the capability of the completed eddy current micro sensors, a defect in form of a scratch was created on the surface of a Cu probe and investigated by eddy current testing. The electrical output signal of the eddy current micro sensor was subsequently compared to an optical measurement of the surface profile of this scratch. There is a high correlation between the optical measurements and the signal of the eddy current micro sensor.