Magnetoelectric Memory Cells Based On Ultrathin FeCo Films

Ferroelectric ferromagnetic heterostructures possess both ferroelectric and ferromagnetic properties,and the conversion between electric and magnetic properties can be realized through strain-mediated magnetoelectric coupling effect,which is of great significance for promoting the development of new magnetoelectric memory devices.In this paper,HfZrO₂/Fe₆₅Co₃₅（HZO/FeCo）and Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃/Fe₆₅Co₃₅（PMN-PT/FeCo）laminate heterostructures are constructed.By applying the external bias voltage,the resistance state of HZO/FeCo and PMN-PT/FeCo composite films is regulated.The specific research content is as follows:HZO ferroelectric thin films were prepared by RF magnetron sputtering.The effects of in situ annealing time,argon-oxygen ratio and working pressure on the phase structure,morphology and electrical properties of the thin films were analyzed,and the preparation process of the thin films was optimized.In addition,structures and properties of HZO films with different substrates and top electrodes were studied.Through the analysis of the crystal structure,ionic valence state and piezoelectric properties of the films,it is shown that the ferroelectric properties of HZO films are further optimized when the upper electrode is Ti and the bottom electrode is Ti N.On this basis,HZO films of different thicknesses were prepared.When the film thickness was 10 nm,the O（111）preferred crystalline growth HZO films were obtained.The saturation polarization,residual polarization and coercive field of the films were 19.8μC/cm²,10.6μC/cm² and 600 kV/cm,respectively,and the piezoelectric displacement was 22.6?.By ion beam sputtering combined with photolithography,FeCo thin film was prepared on the optimized HZO ferroelectric thin film,and HZO/FeCo laminated thin film was constructed.The phase structure,microstructure and multi-iron properties of the composite thin film were characterized,and the regulation effect of bias voltage on the resistance of heterogeneous structure was realized in the laminated thin film structure.The results show that the design and preparation of small-size ultra-thin FeCo film is beneficial to enhance the resistivity transformation rate of the composite film.When the FeCo film is 100μm×100μm and the thickness is 20 nm,the resistance change rate of HZO/FeCo film is 88%.The PMN-PT/FeCo laminated heterogeneous structure was constructed,and the phase composition,morphology,ferroelectric and ferromagnetic properties of the heterostructures were tested and analyzed.The effects of FeCo thin film with different transverse sizes on the resistance change of the heterogeneous structure were studied.It was found that the smaller the transverse size of FeCo thin film,the greater the resistance change rate of the heterostructure.When the transverse size is 100μm×100μm,the resistance change rate reaches 61.5%.By analyzing the elements and ion valence states of the thin films,it is shown that the resistance switching characteristics could be induced by the combination of strain-mediated magnetoelectric coupling effects and charge-driven interfacial effects.