Impedance Change Ratio and Sensitivity of Micromachined Single-Layer Thin Film Magneto-Impedance Sensor

Thin-film techniques are important in the miniaturization of electronic devices. We studied a thin-film magnetoimpedance element made with Co-based amorphous soft magnetic material and developed a highly sensitive magnetic field sensor with high spatial resolution. Thin films are several micrometers thick, and show significant impedance changes as frequencies change from the megahertz to the gigahertz region. Multilayer systems are often used to achieve a large impedance change, but they typically require a complex thin-film structure and a length of several millimeters. Our thin-film sensors have lengths between 30 μm and 1 mm in a simple monolayer configuration and successfully overcome the demagnetizing field. The impedance change ratio was 300% for a 1 mm long element at 1 GHz and between 20-30% at 1 GHz for a miniaturized element of 30 μm. The sensors had a maximum sensitivity of 33.4%/Oe.