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technical paper
Evaluation of Coplanar Line Type Thin Film Magnetic Field Sensor with Narrow Slits.
In our previous work, we developed the highly sensitive thin film sensor and indicated the successful measurement of Magnetocardiogram signals without the magnetic
shielding 1. But the sensitivity was poor around the ferromagnetic resonance frequency (in GHz bands) since the sensor had the severe reflection loss because of the impedance
mismatching 2. In this research, we have improved the impedance matching of the sensor by employing the slits in the magnetic thin-film and evaluated the appropriate slit width. As
shown in Fig. 1, the proposed sensor composes of CoNbZr, SrTiO, and Cu/Cr films. The CoNbZr film was annealed in rotating and static magnetic fields to induce transverse magnetic
anisotropy. Several sensors having 6, 10, 26, 36, and 50 mm slit widths were fabricated and evaluated from the phase and the amplitude of the transmission coefficient (S21) measured by
the network analyzer (Advantest Corp., R3767CG). In the measurement, the DC magnetic field of 0-20 Oe was applied to the longitudinal direction of the coplanar by a Helmholtz coil.
The amplitude of S21 was improved about five times larger by employing the narrow slits. Although the changes of the amplitude and the phase by the magnetic field were small as the
narrow slit, the maximum amplitude of S21 became large. Fig. 2 shows the sensor sensitivity versus the slit width. The sensitivity of the sensor was evaluated by assuming it to be
proportional to the product of the phase and the amplitude gradients as the magnetic field and the carrier signal strength 3. The appropriate slit width was around 10 mm for the coplanar
line type thin film magnetic field sensor and the sensitivity will enhance more than 10 times higher than the sensor without slits 1. However, it is expected that the sensor can get higher
sensitivity by using amplitude modulation.
References:
1 S. Yabukami et al, J. Magn. Soc. Jpn., Vol. 38, pp. 25-28 (2014) 2 T. Ishihara et al, Journal of Magnetic of Japan, vol. 6 (2022) 3 N. Horikoshi et al, Journal of
Magnetic of Japan, vol. 29, pp. 472 (2005)