PUB - Publikationen an der Universität Bielefeld

This thesis is based on a project cooperation with the main goal to achieve a magnetic field sensor array to detect and analyze the leakage of faulty conductive power lines, producing an output image similar to that of an IR camera. For this, two approaches were tested for the buildup.
The first approach is based on the TMR effect by magnetite nanoparticles, which are printed directly between contact pads on a chip. This resulted in a broad TMR curve with insufficient field sensitivity. Hence, a second approach was followed. Here, the triangular-shaped GMR curve of a sputtered Per- malloy/Copper multilayer system exhibits high sensitivity. To reduce the fabrication time and costs, the system is directly sputtered on top of the contact pad of the circuit board.
It could be shown that the GMR effect of the Cu/Py system in the first antiferromagnetic coupling maxi- mum maintains its high linearity and stable GMR value even on substrates with extreme roughness, such as a circuit board, if a buffer system is added. This buffer system was developed and evaluated, and it proved to approximately halve the surface roughness while keeping the GMR value at the same level as for the GMR plus buffer system on an ideal substrate like a Si-wafer. It was also shown that sputtering on larger areas through a mask is feasible. Thus, all necessary steps to realize such a device could be demonstrated.
Moreover, calculations of the magnetic field of a conductive wire and the effect of faulty areas on the magnetic field were performed. Calculations of the exchange coupling constants were also done to ap- proximate the coupling stability and linearity of the systems and their sensitivity. A comparison of the calculation findings shows the possibility of detecting conductive wires as well as faulty areas with the used GMR system.
Furthermore, the temperature stability of the sensor system is tested by DSC. Therefore, the suitability of the DSC for thin films was proven.