Mid-to-Low Temperature Preparation Of CaBi₂Nb₂O₉ Thin Films And Study Of Their Electrical Properties

With the development of the semiconductor industry,the transformation of devices into miniaturization and integration has become an inevitable trend.The efficient combination of ferroelectric functional thin films and CMOS-Si integration technology can realize the integration of sensing,driving,storage,energy storage and other novel devices integration,which has broad application prospects in micro-electromechanical systems,microelectronics and other fields.CaBi2Nb2O9(CBNO)is an environment-friendly ferroelectric material,with many excellent properties,such as anti-fatigue characteristics,low temperature-frequency coefficient,high Curie temperature,and anisotropic electromechanical coupling factor.If CBNO films can be combined with the CMOS-Si substrate,many practical applications will be developed in microelectronics to solve the problems that microelectronic equipments cannot operate under high-temperature and high-frequency environments or aging quickly.However,high temperature(600? or higher)process is almost unavoidable to achieve high-quality CBNO films,and the limit temperature that CMOS-Si can withstand is lower than 500?.In order to be compatible with CMOS-Si integration technology,it is must to lower the growth temperature of films.Besides,the anisotropy of the CBNO film is obvious.It is difficult to improve the electrical properties of CBNO films,because of the uniqe layered structure and the direction contradiction between polarization and growth.In this research,we grow non-c-axis oriented CBNO films to improve their electrical properties on Si substrates via RF magnetron sputtering technology,combined with buffer layer technology,and explore the influence of temperature and substrates on structure and electrical properties.Moreover,further lower growth temperature of films with the rapid annealing process,and explore the best annealing temperature,than optimize the sputtering parameters to obtain CBNO films with excellent ferroelectric,dielectric,and energy storage characteristics.Finally,we can realize the integration of high-performance CBNO thin films on Si substrates at medium and low temperature.The main results of this study are as follows:(1)The SrRu03(SRO)buffer layer improves the interface state between the CBNO film and the Si substrate,as a perovskite seed crystal to guide grains grow along(11 2n+1)perfered orientation,realizing the substitution of grains tilted from a/b-axis to c-axis oriented grains.(2)The substrate temperature and type directly affects the crystallinity and crystalline orientation of the CBNO film,which in turn affects the electrical properties.The SRO-buffered CBNO film prepared at 500? exhibits a strong(117)texture and extremely excellent electrical properties(?r?480@1 kHz,Ps?63 ?C/cm2,Pr?12 ?C/cm2@1800 kV/cm).Furthermore,the film shows good transverse piezoelectric responses e31,f?1.25 C/m2 and temperature-frequency stability with a low dielectric loss(tan??5%)up to 500? under a high working frequency(5 kHz/1 MHz).(3)Rapid thermal processing(RTP)is unavoidable for CBNO films deposited at 350? to obtain ferroelectricity,and the higher the RTP temperature(within a certain temperature range),the more obvious improvement of the CBNO film in structure and electrical properties.The CBNO film annealed at 700? shows the best performance.(4)With the increase of sputtering power,the CBNO film thicken,getting a higher breakdown voltage.Extending the holding time can provide particles more energy for nucleation and growth,enhanceing the crystallinity.The pure oxygen high-pressure holding and cooling atmosphere can reduce oxygen vacancies and defect losses,resulting in the electrical properties optimizing.The annealed CBNO/SRO/Pt/Ti/Si film sputtering at 350?,130 W and holding in high oxygen pressure for 20 minutes shows stronger(115)-oriented texture.Its characteristic hysteresis loop is slender,under an electric field of 2800 kV/cm,Ps?58.5 ?C/cm2,energy storage density?84.2 J/cm3 and the energy storage efficiency?89%,which exploits the research and application of high energy storage capacitors with CBNO thin film.