Microstructural imaging of ferromagnetic material using integrated quantum well Hall-effect sensor arrays

C-W Liang, J Sexton, M Sadeghi and M Missous 

The detailed microstructures of a material can affect its mechanical, electrical and optical properties. In ferromagnetic materials, domain walls and grain boundaries are largely responsible for defining the microstructures. A key method to analyse the microstructure of a ferromagnetic material is to measure the magnetic field leakage (MFL) from its grain boundary/domain walls. The vast majority of materials require a micro-scale magnetic field sensor to image the grains and domains. In this work, high sensitivity low noise quantum well Hall-effect (QWHE) sensor arrays have been designed and fabricated using InGaAs-AlGaAs or metamorphic InGaAs-InAlAs heterostructures. A range of sensor arrays with individual sensor size varying from 400 μm2 down to 4 μm2 were prepared, packaged and mounted onto a precision XYZ stepper platform for magnetic field mapping. Clear images of both micron-scale defects and microstructure are demonstrated and analysed.