Enhancing Film Effective Permeability with Surface Pattern for Sensor Applications

It is commonly known that magnetic sensors are widely used in a range of areas. The adoption of emerging magnetic sensor technology, such as AMR (anisotropic magnetoresistance), GMR (giant magneto-resistance) and GMI (giant magneto-impedance) sensors, is driven principally by their enhanced sensitivity and improved integration performances. At the heart of such sensors is a soft magnetic thin-film element that transduces the magnetic signal due to its permeability feature. What really matters to device performances is the actual permeability (effective permeability) in a film. In this paper, we propose an approach of improving film effective permeability by producing grooved gratings on the film surface. Calculation and finite-element simulation results point out that grooved gratings can partly reduce film thickness so that the demagnetizing factor decreases accordingly. What's more, depending on the groove walls' magnetization, the stray field will in turn increase the applied field strength. Hence, the internal field (the total effective field in the film) is locally enhanced which suggests a better improvement of effective permeability than thinning the film simply. Here we demonstrate that, such grooved films can be applied to improve performances of magnetic sensor device such as a thin-film inductor. Theoretical analysis and simulations show that in the presence of grooved gratings, the inductor performs a wider variation range and a higher variation rate to different applied magnetic fields.