Fabrication Of Flexible Magnetoelectric Heterostructures For Magnetic Sensor Applications

As flexible wearable devices are emerging into people's life,the development of electronic devices tend to miniaturization,flexibility and multifunctionality.Magnetoelectric(ME)heterostructure,which has a wide range of applications in multi-functional electronic and exhibits rich fundamental physics,has attracted tremendous attentions and efforts.Compared with traditional magnetic field sensors,such as fluxgates,Hall probes,and superconducting quantum interferometers,ME magnetic field sensor has advantages of high sensitivity,small size,low power consumption,and low preparation cost.However,in view of flexible electronics applications,it turns to a new challenge how to make a magnetic field sensor with both flexibility and high sensitivity.In this thesis,Metglas was selected as the magnetostrictive phase,Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-Pb Ti O₃(PIN-PMN-PT)piezoelectric single crystals and Pb(Zr_0.52Ti_0.48)O₃(PZT)piezoelectric thick films were chose as piezoelectric phase.Longitudinal-magnetized and transverse-polarized(L-T)mode PIN-PMN-PT/Metglas and multi-push-pull mode PZT/Metglas ME heterostructures were fabricated,respectively.Electrical,mechanical and ME properties of the heterostructures were characterized.The main achievements are as following:1.Firstly,the PIN-PMN-PT single crystals were thinned to 45?m by mechanical polishing method to obtain flexibility.Then,the PIN-PMN-PT/Metglas magnetic field sensor of L-T mode was prepared by combining Metglas alloy foils and PIN-PMN-PT single crystals.The magnetic field sensor exhibits excellent ME performance at an optimum bias field of?3 Oe:at quasi-state(f=1 k Hz),ME coefficient is as high as 63 V/(cm×Oe),and the limit of detection is?1 n T.At resonance(f=43.67 k Hz),ME coefficient is as high as 1.6 k V/(cm×Oe),and the limit of detection is?10 p T.Moreover,the PIN-PMN-PT/Metglas magnetic field sensor maintains a high ME coefficient?35 V/(cm×Oe)under bending angle?=45°,and no obvious deterioration in ME performance occurred after 4000 bending cycles at high strain.Although the magnetic field sensor exhibits flexibility somehow,its maximum bending degree cannot exceed 45°,since the piezoelectric single crystals are brittle.2.In order to prepare a magnetic field sensor with higher flexibility,the flexible PZT piezoelectric thick films were fabricated via sol-gel process assisted by two-dimension mica substrates,which exhibit an ultrahigh piezoelectric coefficient d₃₃?72 p C/N,extending beyond prior art for all-inorganic flexible piezoelectric materials.A multi-push-pull mode PZT/Metglas magnetic field sensor was fabricated by combining Metglas alloy foils and PZT thick films.The magnetic field sensor also exhibits excellent ME performance at the optimum bias magnetic field(H_dc=4.5 Oe):the limit of detection is?100 n T at quasi-state(f=1018 Hz)and the limit of detection is?0.2?T at resonance(f=54.45 k Hz).Moreover,the magnetic field sensor can achieve a bending degree?=80°and no performance degradation was observed after 5000 bending cycles,indicating an excellent mechanical durability.This thesis studied the fabrication of two kinds of ME heterostructures and discussed their performance with regards to the application of flexible magnetic field sensors.The ME magnetic sensor with both high-sensitivity and flexibility provides an effective strategy to realize electric-skin to sense magnetic fields.