Study On Thin Films Magnetoelectric Sensor With On-chip Differential Structure

The magnetoelectric sensor has the characteristics of high sensitivity and resolution,wide response frequency bandwidth and low power consumption.It has broad application prospects in the fields of weak magnetic field detection medical imaging and microwave communication.However,since the core part of the magnetoelectric sensor-the piezoelectric material is highly susceptible to external temperature,the device generates a thermal noise voltage that greatly affects the sensitivity and resolution of the sensor.Therefore,suppressing external thermal noise is important for improving the magnetoelectric response performance of the device in a complex environment.In view of the above problems,this paper intends to give full play to the advantages of film composites in structure and process relative to bulk composites,designing and preparing thin film magnetoelectric sensors with on-chip differential structures to achieve effective suppression of external thermal noise.Firstly,Pb?Zr,Ti?O₃?PZT?and FeCoSiB are used as piezoelectric layer and magnetostrictive layer respectively,and a microbridge type thin film magnetoelectric sensor with strong external noise resistance and good process compatibility is designed.The sensitive element consists of a magnetoelectric unit and a differential reference unit.Through the COMSOL simulation calculation,the change of the thermal response voltage of the magnetoelectric unit and the differential reference unit under the same temperature change was analyzed.According to the simulation results,non-magnetic materials with small differences in thermal physical properties compared with FeCoSiB was selected.This non-magnetic material and PZT constituted a differential reference unit with optimal thermal noise suppression.Secondly,a uniform and dense PZT thin film?¹.2?m?was prepared by pulsed laser deposition?PLD?and sol-gel?Sol-gel?alternating growth on Pt/Ti/SiO₂/Si.The performance test results show that the piezoelectric coefficient of PZT film is about 90 pm/V,and the leakage current density is less than 10^-5 A/cm²,which has higher density and smaller leakage than the film prepared by PLD or Sol-gel alone.FeCoSiB film was prepared by magnetron sputtering.The magnetic co-annealing of FeCoSiB film reduced the coercivity of the film and obtained FeCoSiB film with excellent magnetic properties.Finally,a microbridge type thin film magnetoelectric sensor with double-end fixation and good stability was fabricated by MEMS process,and a differential reference unit composed of PZT/Al was fabricated on the same substrate.The PZT/Al unit and the PZT/FeCoSiB magnetoelectric unit formed an on-chip differential structure.At the same time,a test platform based on LabVIEW software was built to test and analyze the magnetoelectric performance and thermal noise suppression effect of the on-chip differential structure thin film sensor.The test results showed that the optimal bias magnetic field of the magnetoelectric unit is about 6.29Oe,the resonant frequency is 3810Hz,and the magnetoelectric voltage coefficient of the magnetoelectric unit is about 3.98V/cm?Oe.In the case of the introduction of thermal noise from the far-infrared source,the differential structure of thin film magnetoelectric sensor has a minimum detection limit of 35nT,which is 43%lower than that of the non-differential structure?minimum detection limit of 62nT?.The suppression of thermal noise of magnetoelectric sensors has a significant effect,providing a feasible solution and technical path for the design and preparation of high performance thin film magnetoelectric sensors.