Hiroaki Uetake

Highly Sensitive Thin-Film Magnetic Field Sensor Meandering Coplanar Line

A very sensitive thin-film sensor was developed using a meandering coplanar line fabricated from Sr₃₃Ti₁₆O₅₁ film (3 μm thick), amorphous Co₈₅Nb₁₂Zr₃ film (1 mm×2.45 mm, 0.3-2 μm thick), and Cu/Cr film (2/0.1 μm). The deposited SrTiO film enhanced the sensitivity of a magnetic held sensor, a phase change of more than 30°/Oe and a gain of over -40 dB being achieved simultaneously. The maximum phase change (sensitivity) was observed for a CoNbZr film thickness of ~0.5-1 μm. The sensitive bias held and carrier frequency increased as the CoNbZr film thickness increased. The optimum CoNbZr film thickness was realized by the tradeoff between the sensitive bias held and the volume of the CoNbZr film.

Highly Sensitive Coplanar Line Thin-Film Sensor Using SrTiO Film

A very sensitive thin-film sensor was developed using a coplanar line fabricated from SrTiO (Sr₃₃Ti₁₆O₅₁) film (0.5, 1, 2, 3, and 6 μm thick), amorphous CoNbZr film (5 μm thick), and Cu/Cr film (4 μm/0.2 μm). The deposited SrTiO film had high permittivity of around 31. This film enhanced the sensitivity of the magnetic field sensor, a phase change of more than 100°/Oe and gain of over -40 dB being achieved simultaneously. The sensor with SrTiO film enhanced the sensitivity about 1.6 times greater than that with SiO₂ film because of the high permittivity of the SrTiO film. The sensitivity of the sensor increased with increasing thickness of the SrTiO film, a thickness of around 3 μm being sufficient for enhancement of the sensitivity.

Behavior of sensitivity at edge of thin-film magnetoimpedance element

We fabricated thin-film magnetoimpedance elements in which an impedance of each 100 μm section of element can be examined, to investigate impedance changes of each section subjected to a DC magnetic field. The field strength where the impedance peaks shows a larger value at the edge and it decreases toward the center of the element, while the sensitivity is small at the end of the elements and increases toward the center of the element. The obtained results can be explained on a basis of magnetic field simulation and simple impedance model taking into account a distribution of demagnetizing field. A uniformity of demagnetizing field is significant to obtain a higher sensitivity, and intensity of the demagnetizing field strongly affects a magnetic field strength when the impedance peaks. We also clarified an ellipsoidal shape uniform the distribution of demagnetizing field within the element, which contributes to improve the sensitivity of the MI sensor, especially near edge part.

Analysis of thin-film magnetoimpedance behavior in low MHz regions based on domain wall equation and bias susceptibility theory

An interesting behavior of thin-film magnetoimpedance elements in the relatively low megahertz (MHz) region is found experimentally when the width of the element is narrow and the thickness of elements is several micrometers. The impedance peaks and inductance shows a rapid drop at around 10 MHz when a bias field is applied to such elements. The impedance profiles of the elements were analyzed on the basis of a domain wall motion equation and bias susceptibility theory. Calculation of the domain wall motion equation when accounting for domain resonance explains the impedance behavior in the low MHz region. The rapid drop in inductance and peak in impedance can be attributed to the domain wall resonance. At a relatively higher frequency, above 100 MHz, the calculation of bias susceptibility while considering ferromagnetic resonance thoroughly explains the experimental behavior.

Magneto-Impedance of Micromachined Thin Films Less Than 100

Thin-film type magneto-impedance (MI) elements having widths and thicknesses of several micrometers and lengths less than 100 μm in a rectangular shape were fabricated to reduce the demagnetizing effect. Triangular-type MI elements with sensing parts less than 100 μm in length were also fabricated to facilitate near-field detection with a higher spatial resolution. Rectangular-type elements with widths and lengths of 2 μm and 30 μm, respectively, demonstrate a typical MI profile, whereas an element with a 1 μm width shows a discontinuous impedance change and hysteresis due to incomplete anisotropy control. For the triangular elements, we can suppress the distribution of the demagnetizing factor in the sensing part of the elements and obtain typical MI profiles for 30-100 μm lengths.