350% Magneto-impedance ratio in thin-film structures

The Magneto-impedance (MI) effect accounts for the large change of the electrical impedance experienced by soft magnetic materials when a magnetic field modifies its magnetic permeability. MI and related phenomena have been extensively studied in different soft magnetic materials with varied shapes and configurations for a wide range of frequencies. The excellent sensitivity of MI to low magnetic fields is suitable for the development of magnetic microsensors competing in performance with fluxgate magnetometers [1]. Thin film-based MI structures are well suited to fabricate magnetic microsensors using the techniques of the microelectronic industry. Among them, Permalloy (Py) based systems benefits from well-established preparation procedures and enhanced structural stability over amorphous based sensors (important for space applications, for instance). In previous studies we have systematically analyzed the influence of the preparation conditions and the structure on the properties of thin film Py-based multilayers. In this work we determine the optimum combination of magnetic and non-magnetic layers to maximize the MI performance, while maintaining an open flux configuration (Py not enclosing the central non-magnetic conductor), which permits the fabrication of the complete stack of layers in a single process [2]. The resulting configuration was implemented in a series of samples with different lengths and widths prepared by magnetron sputtering and photolithography.