Abstract
Magnetostrictive thin-film coated Surface Acoustic Wave (SAW) devices were promising for sensing magnetic field owing to their superior features as micro-size, fast response, and high sensitivity originated from the magnetostrictive effect. However, the magnetostriction nature in magnetostrictive thin-film causes significantly mechanical fatigue in service, deteriorating the sensor performances. In this work, the fatigue phenomenon in magnetostrictive coating was underlined by characterizing the prepared FeCo thin-film coated magnetic device cyclically. Obvious shedding was observed in FeCo coating after cyclic testing and the magnetic-sensitivity decreases significantly. One of the reasons is the weak adhesion of FeCo thin-film towards the substrate. As an available way allowing enhancement of adhesion, a Cr thin-film was employed as the transition-layer to weaken the mechanical fatigue. However, it accompanied by the issue of the reduced magnetostrictive coefficient and the obstruction in magnetostrain-tranfer to piezoelectric substrate. As a result, the slump in sensitivity was observed. To address such issues, a design of dotted-pattern with Cr transition layer was employed to build the SAW based magnetic-device. High magnetic-sensitivity and excellent long-term stability were achieved because of the release of coercive force in FeCo dots and enhancement of the FeCo adhesion to the substrate.
Highlights
The magnetostrictive materials attracted much attention for sensing magnetic field owing to their high magnetic sensitivity, fast response, high preparation efficiency, and low cost [1]–[5]
A new configuration of magnetic sensor was built by depositing a magnetostrictive thin-film on top of surface acoustic wave (SAW) device [10], [11]
Experimental results indicate that obvious shedding are observed from the FeCo thin-film after cyclic testing, as the result, a slump occurs at the magneto-sensitivity after cyclic testing runs
Summary
The magnetostrictive materials attracted much attention for sensing magnetic field owing to their high magnetic sensitivity, fast response, high preparation efficiency, and low cost [1]–[5]. A new configuration of magnetic sensor was built by depositing a magnetostrictive thin-film on top of surface acoustic wave (SAW) device [10], [11]. A magnetic-sensitivity of 31.5 ppm/mT was achieved from the sensing device with layered structure of Ni/Al2O3/IDT/ LN-Y128◦ when device operating at 815 MHz [12]. Larger shift of 0.64% in SAW velocity was predicted from a 500 nm Galfenol thin-film coated SAW device operating at 158 MHz [13]. A maximum SAW velocity shift close to 20% was obtained from a multilayered sensing structure of TbCo2/FeCo/LiNbO3 for the shear horizontal wave mode as a ratio close to 1 between magneto-elastic film thickness and wavelength [14]. High frequency sensitivities of 8.3 kHz/mT, 17.72 kHz/mT and 21.17 kHz/mT
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