Design And Preparation Of Sc-doped AlN Thin Film

In recent years,the communication industry has developed rapidly.Since 2019,the number of 5G base stations has grown rapidly,and filters play an important role in it.Previously,the filters made of lithium niobate single crystal were not easy to be integrated and used in combination with other devices.Today,as electronic components are required to be miniaturized,integrated and interconnected,new solutions need to be proposed.As a passive filter,the surface acoustic wave(SAW)filter is mainly composed of piezoelectric devices and external circuits.Piezoelectric thin films play a key role in piezoelectric devices.AlN has high chemical stability and good temperature stability,and can be used in high temperature applications.Its thin film has high sound velocity,is compatible with CMOS technology,and has low cost.AlN thin film with good C-axis orientation has certain piezoelectricity,and has applications in many fields such as communication,aerospace and military industry.AlN thin film is selected as the research object in this Thesis,and the piezoelectric properties are improved by doping it with Sc element.A model was built in materials studio,and first-principles were used to calculate the variation law of specific parameters such as elastic constant,crystal axis ratio change and piezoelectric pressure response of AlN with the change of Sc doping concentration.The conclusion of the improvement of the piezoelectricity was obtained,and the mechanism of the improvement of the piezoelectricity was further analyzed.After that,the Sc_xAl_1-xN thin film was grown on the sapphire substrate by means of magnetron sputtering vacuum coating,and the Al-Sc alloy target with 20%scandium atom content was used as the representative to study the sputtering power and sputtering temperature.The effects of nitrogen-argon ratio and sputtering gas pressure on the quality of Sc_xAl_1-xN thin films were discussed in detail from the perspectives of crystal quality,surface morphology analysis,roughness analysis and deposition rate analysis.Through the comparison of process parameters,it is found that various factors mainly change the film quality by changing the field strength,the self-bias effect of the target and the sputtering atmosphere,affecting the particle energy,changing the deposition rate,and changing the reaction and bonding of the particles on the substrate surface.When the sputtering power and temperature are too low,the kinetic energy obtained by the particles is small,which is not conducive to the growth of the C-axis preferential orientation.This results in increased roughness and decreased crystalline quality.The ratio of nitrogen to argon is an important factor affecting the quality of the film.When the concentration of N2 on the surface of the substrate is insufficient,its c-axis orientation is poor,and finally a good crystal quality is obtained at the concentration of 6:17.The electromechanical coupling coefficient of 12.17%is obtained through the fabrication of the micro-acoustic thin film resonator and the test of the frequency curve,which is a certain improvement compared with the pure AlN device.After theoretical research,process preparation and device performance analysis,this thesis concludes that Sc-doped AlN films can improve the performance of piezoelectric devices,and there are optimal parameters for the film preparation process.