Study On The Magnetoelectric Surface Acoustic Wave Sensor With Ultrahigh Magnetic Field Sensitivity

In the past ten years, magnetoelectric composite has attracted a lot of attention because of the ultrahigh magnetic field sensitivity as much as 10-11 Tesla/Hz1/2. However, it also meets a very serious challenge in the application because of poor magnetic field sensitivity when sensing DC and low frequency magnetic fields, large size and significant noise due to ferroelectric loss and pyroelectric effect. In order to solve these problems, a magnetoelectric surface acoustic wave magnetic field sensor(SAWMS) based on the heterostructure of ZnO/Metglas semi-infinite substrate has been proposed. Our calculations show that very high sensitivity can be achieved even in sensing DC and broad-band AC magnetic field. The other merits of such a sensor include high temperature stablility, integratable, and wireless communication ability. The main work of this thesis is as follows:1. The scattering matrix method was adopted to solve the surface acoustic wave propagation problem in the ZnO/Metglas semi-infinite substrate. Only one mode of surface acoustic wave was found, and the velocity of the SAW is between 2259.1 m/s and 2679.2 m/s. When fHZnO is less than 0.96 GHz·μm, the electromechanical coupling coefficient value first increases then decreases with the peak value 0.68%. When fHZn O is more than 3.85 GHz·μm, the electromechanical coupling coefficient value increases from 0.1% to 0.95%, and then almost saturates. The phase velocity of the SAW resonator with fHZnO<0.96 GHz·μm changes more dramatically upon varing the Young?s modulus of Metglas. To ensure the normal operation of the SAWMS, there is a upper limit value of fHZnO. Furthermore, we have also compared AlN/Metglas semi-infinite substrate with ZnO/Metglas heterostructure in construction of the SAWMS.2. The same surface acoustic wave propagation problem in the ZnO/Metglas semi-infinite substrate was sovled by using COMSOL Multiphysics software. The results of this method are completely consistent with that of the scattering matrix method.3. The surface effective permittivity method was adopted to study the effect of the parameters of interdigital transducer, such as the pitch width, the number of electrode pairs, overlap length, et al, on the relative bandwidth, insertion loss and magnetic field sensitivity of the SAWMS. The parameters of the IDT are optimized. In addition, the magnetic field sensitivity was analyzed using the COMSOL, which turns out to be as high as 10-11 Tesla. Additonally, it is shown that thinner ZnO film and narrower IDT pitch width contribute to higher magnetic field sensitivity.4. Highly c-axis oriented ZnO film was successfully deposited on the Metglas amorphous ribbon using magnetron sputtering at a low temperature of 350℃. The full width at half maximum is only 4.28o. The thickness of film is 600 nm, and the surface roughness is 4.1 nm. The ribbon remains amorphous after ZnO film deposition, and no obviously change of magnetic properties was found between the as-received and after deposited Metglas ribbon, therefore, confirming the feasibility of our proposed magnetic field sensor.