Magnetoimpedance Characteristics on Micromachined Thin-Film Elements Less Than 100-Micrometers Length

Abstract

Magnetoimpedance (MI) sensor has higher sensitivity, thus it is expected to be applied to the medical applications and the nondestructive evaluation, etc. With the demands for the detection of local and micro area, the miniaturization of the sensor element is strongly required. Though a thin-film MI element contributes to the miniaturization of the sensor elements, the demagnetizing effect becomes significant as the problem to be solved [1]. In this study, to reduce the demagnetizing effect, the sensor elements with narrower width, the specific shape and length less than 100 $\mu \text{m}$ were fabricated by the micromachining techniques, and the impedance of the elements were evaluated. In the fabrication process, Focus Ion Beam was used for the elements with width less than 5 $\mu \text{m}$ . The shapes of sensor elements were rectangular and triangular as shown in Fig. 1. The fabricated elements have from 1 to 20 $\mu \text{m}$ wide, from 30 to 100 $\mu \text{m}$ long and 1 or 2 $\mu \text{m}$ thick, and have an easy axis parallel to the width direction. Fig. 2 shows the impedance changes of the elements against the applied magnetic field. The AC current with 100 MHz and the DC magnetic field were applied to the length direction of the elements. The impedance for the rectangular elements with wider width, 10 or 20 $\mu \text{m}$ , have no change, which is attributed to the strong demagnetizing field. We confirmed this point by the electromagnetic analysis. On the other hand, the triangular and several rectangular elements with narrower width, the impedance shows the typical MI profile. Additionally, other several elements, rectangular with 1 $\mu \text{m}$ wide and 30 $\mu \text{m}$ long or 2 $\mu \text{m}$ wide and 100 $\mu \text{m}$ long, show the impedance jumps. This jump is caused by the inclined easy axis, which means the easy axis is not kept parallel to the width direction owing to the demagnetizing effect in the width direction. The impedance changes of the elements with 30 $\mu \text{m}$ long were demonstrated, which contributes to development of MI sensor with a high spatial resolution.