Fabrication Of Highly-oriented Bi₅FeTi₃O₁₅Bismuth Layer-structured Ferroelectric Thin Films Via RF Magnetron Sputtering And Investigations Of Their Properties

To our knowledge,bismuth-layer structured ferroelectrics are non-lead information functional materials.They have a prospective blueprint in the field of high temperature and high frequency industrial applications and non-volatile ferroelectric memories,attributed to the facts that their Curie Temperature is high,in addition,they have low dielectric constant,low leakage current,low aging rate and good anti-fatigue effect,etc.Compared to bismuth-layer structured ferroelectrics,the traditional PZT piezoelectric ceramics have a lower Curie Temperature,also,they contain toxic substance;Though Tungsten bronze piezoelectric ceramics have high Curie Temperature,their poling condition is harsh,as a result,their piezoelectricity is small.Ferroelectric thin films fabricated by RF magnetron sputtering have a series of merits,such as,small size,light weight,low working voltage required by the semiconductor integration,meeting the requirements of the functional development of electronic components to minimization and integration.In this research,the author synthesis Bi₅FeTi₃O₁5 bismuth-layer structured piezoelectric ceramics and targets via traditional solid-state sintering,the microstructure,surface topography and electrical properties（dielectric properties,ferroelectric properties and piezoelectric properties）are comprehensively investigated and analyzed.The result reveals that the piezoelectric targets also have excellent electrical properties.After the fabrication of the piezoelectric targets,the ferroelectric thin films are fabricated by RF magnetron sputtering technique,based on "stress engineering","size effect" and "deficiency chemistry".The phase structures are determined by X-ray diffraction technique;the surface topography is investigated by Scanning Electron Microscope;the dielectric properties,such as,the dielectric spectrum and dielectric temperature spectrum are measured by an Agilent 4294A precision impedance analyzer in accordance with the standard of IEEE;the ferroelectric properties,such as,the hysteresis loop,the leakage current curve,and the PUND（positive up and negative down）,are measured by using a ferroelectric performance tester.The investigated results are as followed:（1）Among the piezoelectric series,the stoichiometric one has the best piezoelectric response,with the piezoelectric constant（d33）up to 18 pC/N,the mechanical quality factor up to 2925 and the Curie Temperature up to 760 ℃,in addition,all the four components show anisotropy in electromechanical properties.（2）Investigate the influence of process parameters,such as,the sputtering temperature,the sputtering power,the sputtering pressure,the sputtering atmosphere,the cooling atmosphere etc.on the phase structures,the surface topography and the electrical properties of the ferroelectric thin films.The phase structures,the surface topography and the electrical properties of the optimized Bi/Ti/Pt/BFTO heterostructure ferroelectric thin films are comprehensively revealed.（3）MgO/SRO/BFTO and Si/YSZ/SRO/BFTO heterostructure ferroelectric thin films with excellent performance are fabricated.The results show that the film（b）of MgO/SRO/BFTO series has the largest dielectric constant,up to 447,measured at 1 KHz;Also,we can claim that,the two group heterostructrue ferroelectric thin films are polycrystalline structured,with a substantial amount of a grain,the phase microstructure of film（a）of Si/YSZ/SRO/BFTO series is nearly（0180）epitaxial.（4）The different orientated Strontium Titanate（SrTiO₃）are selected as the substrate to deposited STO/SRO/BFTO heterostructrue ferroelectric thin films,and investigate the influence of orientation of substrate on the phase structures,the surface topography and the electrical properties of the ferroelectric thin films.X-ray diffraction patterns reveal the epitaxial relation are BFTO（001）//SrTiO₃（001）,BFTO（082）/（280）//SrTiO₃（110）and BFTO（2216）//SrTiO₃（111）.The dielectric properties of the ferroelectric thin films exhibit strong anisotropy based on the orientation of the substrate,among this series,the ferroelectric thin films deposited on the（001）orientated substrate,has the largest dielectric constant,up to 628,measured at 1 KHz.