Abstract
Temperature compensation is critical and important for surface acoustic wave (SAW) magnetic field sensors. In this study, a Love wave mode based SAW device is investigated as a magnetic field sensor. The considered structure is composed of a CoFeB magnetostrictive film as sensitive layer, SiO2, and ZnO film as insulating and temperature compensation layers and ST+90°-cut quartz as substrate. A theoretical model is proposed to study the magnetic field sensitivity and temperature coefficient of frequency (TCF) variations. Optimized structures by calculation were fabricated and characterized and obtained results show a good agreement between experiments and our model simulation. We clearly shown that signal performances as well as the flexibility of the resonator design were improved by adding the isolating SiO2 layer. Thus, a sensor showing a near zero TCF (0.1 ppm/°C) and a magnetic field sensitivity of −420 ppm/mT was achieved with the structure CoFeB(100 nm)/SiO2(250 nm)/ZnO(300 nm)/Quartz(ST-X+90°). This multi-layered structure is beneficial to design reliable SAW magnetic field sensors.
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