Thin-Film Magneto-Impedance Sensors

Abstract

We review the state-of-the-art of thin films displaying the magneto-impedance (MI) effect, with focus on the aspects that are relevant to the successful design and operation of thin film-based magnetic sensors. After a brief introduction of the MI effect, the materials and geometries that maximize the performance, together with the measurement procedure for their characterization, are exposed. A nonexhaustive survey of applications is included, mostly with the aim of displaying the capabilities of thin film structures in the field of magnetic sensing, and the variety of topics covered by them. A special emphasis is made on some concepts that are not commonly treated in the literature, such as the influence of the measuring circuit on the magneto-impedance ratio, the geometry optimization by means of numerical simulation by finite element methods, or noise measurements on thin films. Additionally, a brief description of the patterning procedure by photolithography is included, since the major advantage of thin film sensors over other types of magneto-impedance materials as ribbons or wires is the possibility of patterning the sensible element in micrometric shapes, and most of all, their easy integration with the interface microelectronic circuitry.