Study On Preparation Process And Doping Modification Of NTC Thin Films

With the rapid development of modern integrated circuit technology,electronic components are moving toward miniaturization and low resistance.NTCR?Negative Temperature Coefficient Resistance?is an important member of sensitive electronic components with wide application value in circuit protection and temperature measurement.Therefore,this paper aims to prepare a thin film NTC thermistor with lower room temperature resistance value,high thermal constant B value and good temperature stability.The study was focused on Mn_1.56Co_0.96Ni_0.48O₄ NTC material which has the lowest resistivity in bulk.Then,the thin film NTC thermistor was prepared with a structure of Ag/NTC/SiO₂/Si by sol-gel method.Finally,a series of studies were investigated including the preparation process,doping to reduce resistance and doping to improve aging performance.Firstly,the influence of preparation process on Mn_1.56Co_0.96Ni_0.48O₄ film was investigated.The best heat treatment temperature for spin coating was 200?,and the thickness of spin coating was 10 layers.During the annealing process,it was found that a better spinel structure was formed above 550?,and the optimum annealing temperature was 750?.It was found by SEM that the film was the densest at this time and the room temperature resistance was the lowest.The film was annealed at 750?for 1 h to obtain a film room temperature resistance value R₂₅=0.34 M?,and a thermal constant B_25/50=3560 K.Secondly,in order to further reduce the room temperature resistance value R₂₅ of the film,the effect of Cu doping on the film of Cu_xMn_1.56Co_0.96Ni_0.48O_4+y?x=0⁰.25,3+x/4+y=3/4?was investigated.It was found that a small amount of Cu?x?0.2?doping can rapidly reduce R₂₅,and when Cu?x>0.2?is excessively doped,R₂₅increases instead.XRD analysis shows that the lattice shrinkage and lattice constants decrease with the addition of Cu.At the same time,it was found through microstructural testing that a small amount of Cu?x?0.2?doping promoted the grain growth of the film to be dense,when Cu?x>0.2?was excessively doped,new pores are generated.It was found by XPS analysis that the Cu ions in the film mainly occupy the oxygen tetrahedral position?A site?in the form of Cu⁺.With the increase of Cu content,the content of Cu⁺and Mn³⁺/Mn⁴⁺ions increased,which enhanced the conductivity and decreased the room temperature resistance.The film aging performance decreases as the amount of Cu doping increases.When x=0.2,the film has the lowest room temperature resistance value R₂₅=0.082 M?,and the thermal constant B_25/50=3250K.Finally,in order to improve the aging properties of Cu-doped films,Ca?calcium?doping was investigated for Ca_xCu_0.2Mn_1.56Co_0.96Ni_0.48O_4+y(x=0⁰.15,x+3.2/4+y=3/4The effect of the film.Studies have shown that a small amount of Ca?x?0.05?doping can significantly improve the aging performance of the film and reduce the aging rate without significantly increasing the room temperature resistance R₂₅ and not significantly reducing the thermal constant B value.It was found by SEM that Ca inhibited the grain growth of the film and made the grain smaller.As the amount of Ca doping increased,the film gradually became dense and pores and defects were generated.When the doping amount x>0.05,the aging rate increases instead because the defects and pores make the metal cations more easily migrated and rearranged,and the resistance drift increases.When the Ca doping amount is x=0.05,the room temperature resistance value of the film is R₂₅=0.123 M?,the heat sensitivity constant B_25/50=3400 K,and the aging rate?R/R=21.1%.