Exploring The Microstructure-Electromechanical Property Relationship In Perovskite Ferroelectric Films

Originated from its excellent ferroelectricity,piezoelectricity and pyroelectricity and other characteristics,perovskite(ABO3)ferroelectric thin films are one of the most important kinds of functional devices in the microelectronics industry,such as ferroelectric random access memories,RF-MEMS switch,ultrasonic motor infrared detectors and so on which can realize the conversion between electrical energy and electrical energy,mechanical energy and electrical energy,thermal energy and electrical energy,or light energy and electrical energy.These applications make it play an increasingly important role in many core and emerging fields such as big data,mobile computing and automation control.Notably,the ferroelectric thin films which is in common use in electronic devices are single component with a polycrystalline structure,small remnant polarization and poor electrical performance.Hence it also could not reflect the great advantages in using the substrate to realize the epitaxial growth of the film,and seriously hinder the ABO3 ferroelectric thin film heterostructures in exploring high performance.and microelectronic industrial application.Therefore,preparing epitaxial ABO3 ferroelectric thin film in which stress controlling together with tuning phase may help in design and control heterogeneous polydomain structure,and observing the phase structure and domain structure evolution under stress and applied electric field has a very important theoretical significance and application value.In the part of experimental research,titanate-based perovskite ferroelectrics were used as target to growing epitaxial/highly oriented film.These films were deposited by using multiple target radio frequency magnetron sputtering(RFMS).The evolvtion of phase and domain structure were studied,and the relationship between microstructure and electrical properties were also discussed.The main research contents are summarized as follows:(1)Based on the elastic domain theory,the stress originated from the lattice mismatch could be released to form T/R heterophase polydomain and hierarchical R-phase polytwins.The epitaxial BZT ferroelectric thin films were prepared on different substrates such as LAO,LSAT and STO.The phase structure and domain structure were verified and studied by XRD,TEM,SHG and AFM measurement.The electrical properties such as temperatures,frequency and bias voltage dependence of ferrolelectricity and dielectricity were characterized.The formation of T/R heterophase polydomains and hierarchical R-phase polytwins can make a great improvement in energy storage density,together with a great contribution to the energy storage efficiency in BZT thin films.(2)(1-x)BaTiO3-xBaSnO3(BT-xBS,0?x?0.20)perovskite thin films were deposited on Pt/Ti/Si substrates with uniaxial graded composition by using a dual-target combinatorial sputtering technique.These films were highly(101)-oriented and showed strong composition dependence in their electromechanical properties.The maximum value of the relative dielectric constant was 925 at around x = 0.028,where the transverse piezoelectric coefficient |e31,f| also peaked at about 1.5-1.9 C/m2.This|e31,f| value is higher than those of epitaxial BaTiO3 thin films.Our results indicate that BT-xBS is a promising substitute of lead-based perovskites for applications in piezoelectric MEMS devices.(3)Epitaxial Pb(Zr0.53Ti0.47)O3 films were grown on(001)Pt/(001)MgO via rf-magnetron sputtering.Switching dynamics of 90° and 180° domains under bi-polar electric fields were probed by using small-field e31,f measurements in which evolution of the transverse piezoelectric response with the bias voltage represents a set of fingerprints of the evolving domain structure.Furthermore,the asymmetric e31,f-V curves revealed a strong built-in electric field,which was verified by the standard polarization-electric field hysteresis measurement.Lastly,X-ray 2?-scan patterns under DC bias voltages were collected for the piezoelectric specimen.The domain switching sequence indicated by the XRD results is consistent with that revealed by the e31,f measurement.