The Research Of Fabrication And Performance Of Galfenol/Diamond MEMS Magnetic Sensor

Magnetic sensors play an increasingly important role in human life.High-reliability intelligent magnetic sensors are in demand in high-temperature environment,such as space exploration,oil development and nuclear industrial.Up to now,the current high-temperature magnetic sensors hold the serious physical limitation and materials drawbacks,which lead to the poor magnetic sensitivity and poor reliability.In general,the material properties are degraded by high temperature,which will result in the failure of the devices function.Diamond material has excellent mechanical,physical,electrical,and chemical inertness,which make it an ideal material to fabricate high-reliability functional devices.Galfenol?FeGa?film hosts high magneto-strictive coefficient and the high Curie temperature,which make it a promising material to produce some components of high-temperature magnetic sensing devices.Thus,to circumvent the challenge in high-temperature magnetic sensing,a novel device concept of interface integration of single-crystal diamond?SCD?MEMS resonator with a huge magneto-strictive coefficient Galfenol?FeGa?film is proposed to realize high-temperature magnetic sensing with high sensitivity and high reliability.In this work,at the first time,FeGa films are grown SCD substrates.The optimal growth process and performance-influenced mechanism are studied.The mechanisms of controlling the microstructure orientation and performance characteristics of FeGa thin films through the interface engineering are described.The thermal-stability of microstructure and magnetic properties of FeGa films are analyzed in details.The SCD MEMS resonators are fabricated with high-stability.Based on?E effect,magnetic sensing of the multilayer MEMS resonance magnetic sensor from room temperature to high temperature is achieved.The target of this work is to focus on the basic research of the application of FeGa/SCD MEMS resonance magnetic sensors.The key conclusions are obtained as follows:1)The research of the growth process and properties of FeGa films on SCD substrates.The FeGa films are successfully grown on SCD substrates through magnetron sputtering technology.The microstructure and magnetic properties of FeGa thin films are studied by altering the growth parameters?working pressure,power,gas flow and time?.The surface roughness,grain size and thickness of FeGa films are proportional to the parameters of working pressure,power and growth time.The surface roughness of FeGa film is inversely proportional to the gas flow.Low pressure can result in obtaining FeGa film with high coercivity?Hc?,low saturation magnetization?Hs?and high remanence ratio?Mr/Ms?.The long growth time is beneficial to obtain FeGa film with low Hc,low Hs and high Mr/Ms.The gas flow and power exhibit weak influence on Hc and Mr/Ms of FeGa film.It is concluded that the optimal growth parameters of FeGa thin film are 1 Pa,10 sccm?Ar?,100 W,4 h.2)The research of the structure and thermal-stability mechanism of FeGa films by interfacial engineering.The interface lattice mismatch is improved through adding the interlayers of Ti,WC and WC/Ti films,which can regulate the microstructure of FeGa films on SCDs.In the structures of FeGa/SCD and FeGa/Ti/SCD,the crystal planes of FeGa films mainly exhibit?220?orientation.For FeGa/WC/SCD and FeGa/WC/Ti/SCD structures,they mainly show?200?orientation.The interlayer layer can enhance the interface bonding force and reduce the internal residual stress of FeGa film,which can improve the morphology and the interface thermal-stability of FeGa film.Amongst these structures of FeGa/SCD,FeGa/Ti/SCD,FeGa/WC/SCD,FeGa/WC/Ti/SCDs,FeGa films can maintain good surface morphology and phase-structure stability when annealing temperatures are not higher than 573 K,773 K,573K,673 K,respectively.At the corresponding annealing temperature,the Ms and Hc of FeGa films in these structures can change within a small range,maintaining the good thermal-stability.Furthermore,in these structures,the thermal-stability of magneto-strictive coefficient of FeGa films can be significantly enhanced by the interlayers.3)The research of the vibration behavior of SCD MEMS resonators.Ion-implantation assisted lift-off?IAL?technology is utilized to produce SCD MEMS cantilever devices.In this work,the quality?Q?factor of the SCD cantilever is intensively determined by the volume effect and surface dissipation.During the continuous heating process,the temperature coefficients of the resonance frequency of SCD cantilevers are below 3.2ppm/K.The Q factors decrease with the temperature increasing,but remain above 3000.During the heating-cooling cycle,the resonance frequency variations of SCD cantilevers measured at room temperature are less than 2×10^-4.For each target temperature,the Q factors measured at room temperature fluctuate in a small range,having the good thermal-stability.4)The research of the magnetic sensing performance of multilayer SCD-based MEMS sensor.Based on?E effect,the structure of the SCD MEMS resonator coupling with FeGa film is used to fabricate magnetic sensor for the first time.The as-deposited FeGa film has no effect on the resonance vibration characteristics of the SCD MEMS cantilever.The FeGa/SCD MEMS resonator magnetic sensor shows stable magnetic sensing performance from room temperature to high temperature.The operating temperature is up to 573 K,with magnetic detection sensitivity up to 7.3 Hz/m T,the inherent magnetic sensor noise of 530 pT/?Hz,and the minimum detectable magnetic field of 159 pT.Furthermore,the effect of the interlayers of Ti,WC and WC/Ti films on magnetic sensing performance of the multilayer SCD-based magnetic sensors is observed.Among these four types of sensors,FeGa/SCD structure-based magnetic sensor holds the weakest magnetic sensitivity.The FeGa/WC/Ti/SCD structure magnetic sensor has the best magnetic sensitivity.The maximum stable operating temperatures of FeGa/SCD,FeGa/WC/SCD,FeGa/Ti/SCD and FeGa/WC/Ti/SCD structures-based magnetic sensors are 573 K,573 K,773 K,and 673 K,respectively.At the temperature of 773 K,the magnetic sensing performance of the FeGa/Ti/SCD structure-based magnetic sensor is stable,illustrating the magnetic sensitivity of 71.1Hz/m T,the tested magnetic noise of 10 n T/?Hz,and the theoretical magnetic noise of212.4 pT/?Hz.This high-temperature magnetic sensing performance is superior to the world-advance level.5)The research of the mechanism of temperature-enhanced?E effect and the regulation of azimuthal magnetic sensing performance based on FeGa/Ti/SCD structure.The magnetic sensing stability of the multilayer structure magnetic sensor can be improved by the heating-cooling process treatment.As the temperature increases,the amplitude of the atomic vibration of the interface material increases,which results in enhancing the interaction of interface atoms.The behavior of the enhanced?E effect induced by temperature is attributed to the strong strain-coupling arised from the atomic thermal-vibration at interface.The?E effect exhibits positive temperature-dependence with the law of Tⁿ.The value of n is determined by the size of the resonator.The?E effect shows the strong relationship with the azimuthal angle in sine-function at 300 K and 773 K.