Preparation Of Potassium Sodium Niobate Based Lead-free Piezoelectric Thin Films And Study On Their Electrical Properties

Potassium sodium niobate（KNN）lead-free piezoelectric material is considered as one of the most promising candidates to replace lead-based piezoelectric materials due to its excellent ferroelectric and piezoelectric properties,high Curie temperature,as well as biocompatibility.Therefore,it can be used in sensors,transducers,actuator,biotechnology and other fields.With the development of micro-electromechanical systems（MEMS）,electronic components are gradually miniaturized and integrated.The preparation of high-quality KNN thin film has become a hotspot in the field of piezoelectric materials.In this paper,we mainly use sol-gel method to prepare KNN based film.By adjusting the parameters in the process of preparing the film,doping elements and producing epitaxial film through orientation control,we use these methods to improve electric properties of the film.The main research contents and conclusions are as follows:（1）Preparation of thin film by adjusting the processing parameters.The effects of chemical additives polyvinyl pyrrolidone（PVP）,heating process before pyrolysis,pyrolysis temperature and annealing mode on the electrical properties of KNN nanofilms were investigated.The results showed that the grains are bonded to each other and grain boundaries are blurred of thin films prepared after adding PVP to the sol,and the films displayed a typical hysteresis loop,and the leakage current density had dropped by nearly three orders of magnitude.In addition,the leakage current density of the film obtained by the rapid heating process,the pyrolysis temperature of500℃and the one-time annealing method is significantly reduced,and the electrical performance of the film is improved.（2）K_0.5Na_0.5Nb_（1-x）Sb_xO₃（x=0,0.04,0.08,0.12）thin films with different Sb content were prepared on Pt/Ti/Si O₂/Si substrates by using optimal processing parameters.The influence of Sb element on the electrical properties of the films was investigated.The results suggested that the piezoelectric properties,dielectric constant and capacitance of the films increased first and then decreased,and it had a relative maximum value when the doping content is x=0.04.However,the leakage current density showed an increasing trend with the increase of Sb content.（3）Based on the optimum doping content of Sb,0.95K_0.5Na_0.5Nb_0.96Sb_0.04O₃-0.05Ca Ti O₃thin film was prepared on Pt/Ti/Si O₂/Si substrate by doping Ca Ti O₃.The co-doping effects of Sb and Ca Ti O₃were explored on microstructure and electrical properties of thin films.The results showed that the surface defects of KNNS-CTO thin films were reduced and the density is increased since the grains bonded more closely.The piezoelectric and ferroelectric properties of KNNS-CTO films increase significantly.Additionally,the leakage current density decreased by three orders of magnitude compared with pure KNN films under high electric field.（4）K_0.5Na_0.5Nb_（1-x）Sb_xO₃（x=0,0.04,0.08,0.12）epitaxial films with different Sb content were prepared on Nb:SrTiO₃substrates by sol-gel method.The effects of element doping on the piezoelectric properties of KNN thin films on different substrates were investigated.The results showed that pure KNN epitaxial films exhibit obvious piezoelectric and ferroelectric properties,and the films had the downward self-polarization.Besides,the piezoelectric response has a relative maximum value when the doping content is x=0.08.