A temperature compensated magnetic field sensor based on the combination of CoFeB ferromagnetic thin films and Quartz/ZnO Love waveguide platform is developed and optimized. The Love wave is a shear horizontal guided wave and therefore provides an optimal interaction with magnetisation in the magneto-elastic thin film resulting in higher acoustic wave magneto-elastic coupling compared to the conventional Rayleigh wave based devices. ST-cut Quartz was chosen as substrate, ZnO as insulating layer for Love wave generation and temperature coefficient of frequency (TCF) compensation and CoFeB as the magnetostrictive layer sensitive to magnetic field. Experimental results show a magneto-acoustic sensitivity of 15.53 MHz/T with almost zero TCF.

wireless magnetic sensors are designed to detect magnetic anomaly and are used for street installation, traffic control, and detection of the parking space availability. The sensor responds to changes in the earth's magnetic field caused by the presence of a vehicle, generally a metallic structure. Installation would be easier and cost-effective if the sensors are batteryless and could be installed into the asphalt or pavement (i.e., buried), thereby eliminating the risk of degradation and the need for regular maintenance, particularly the change of batteries. Another application example for wireless magnetic sensors concerns remote electric current sensing including transient-state electric currents on overhead power lines. Indeed, the development of smart grids requires the development of reliable and low-cost sensor networks. Monitoring electric currents at present and especially in medium and high voltage power lines is difficult and expensive when installing conventional sensors. [1,2] The indirect measurement of electric currents through the generated magnetic fields is an elegant solution. The sensor must also be insensitive to the temperature of the wire that strongly depends on the electric current flowing.Surface acoustic wave (SAW) devices are key components in communication systems and are widely used as filters, delay lines or resonators. They are still relevant for the development of 5G compatible technologies. [3,4] Because SAW devices are highly sensitive to physical parameters that affect SAW velocities, they also offer promising solutions as sensors in a wide range of applications. [5][6][7][8] SAW sensors have the advantage of being micro, passive, wireless, and even packageless in specific configurations. [9][10][11][12] SAW sensor technology allows simultaneous and independent measurement of temperatures and magnetic fields (i.e., electric current). SAW devices based on ferromagnetic films have been studied for the development of magnetic field and electric current sensors. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] However, the environment temperature is a factor affecting the performance of SAW sensors. An unavoidable fact is that SAW magnetic field sensors without temperature compensation are sensitive to both magnetic fields and temperatures due to the negative temperature coefficients of ferromagnetic films. [26,29] It leads to a difficulty in discrimination between them or their simultaneous measurement. Therefore, a SAW sensor that measures A one-port surface acoustic wave (SAW) resonator based on Co 40 -Fe 40 -B 20 / SiO 2 /ZnO/quartz multilayer structure and exhibiting a dual mode, Rayleigh and Love wave modes, is investigated to achieve a multifunctional sensor measuring both temperatures and magnetic fields. The Rayleigh wave mode of the resonator is used for temperature measurement with a temperature sensitivity of −37.9 ppm/°C, and the Love wave mode is used for magnetic field measurement. Co 40 -Fe 40 -B 20 is the magnetic sensitive layer, and quartz crysta...

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.