Study On Preparation And Properties Of NTC Thermal Thin Film By Magnetron Sputtering

Negative temperature coefficient resistance(NTCR)are widely used in electronic components,such as temperature sensor,infrared detection and other fields.With the development of electronic components towards miniaturization,microminiaturization and integration,NTC thermal film have the advantages of high sensitivity,fast response speed,low working voltage and easy integration,etc.It has become the current research hotspots of NTC thermistors.However,it is difficult to prepare the thin films with low room temperature resistance,high thermal constant and good thermal stability.In this paper,excellent comprehensive performance NTC thin films were prepared on SiO₂/Si substrate by magnetron sputtering alloy target,and then annealed and oxidized in air.The preparation process and doping were studied.Firstly,the influence of preparation process on the microstructure and electrical properties of Mn_1.56Co_0.96Ni_0.48O₄ thin film was investigated.The results show that thin film under the annealing temperature of 650?900?has spinel structure,and the surface is uniform and dense without obvious defects.The best preparation process is the annealing temperature of750?,the holding time of 120min,and the cooling rate of 5?/min.The thin film prepared under these conditions has room temperature resistance R₂₅=71.1k?,the thermal constant B_25/50=3305K,and the aging coefficient?R/R=5.21%.The thermal thin film has better comprehensive performance but the room temperature resistance and aging coefficient are slightly higher.Then,in order to further reduce the room temperature resistance R₂₅ of Mn_1.56Co_0.96Ni_0.48O₄ thin film,Mn_1.46Co_0.86Ni_0.48Cu_0.2O₄ thin film was prepared by doping Cu element.The results show that Cu doping can greatly reduce the room temperature resistance of the thin film,but it will make the aging properties of the thin film worse.The preparation process is the annealing temperature of 750?,the holding time of 120min,and the cooling rate of 5?/min,the room temperature resistance R₂₅=17.3k?,the thermal sensitivity constant B_25/50=3103k,and the aging coefficient?R/R=8.63%.XPS was used to analyze the Cu doped thin film.The results show that the Cu element mainly exists in the form of Cu⁺in the tetrahedral position(A site)of spinel structure.The doping of Cu element can increase the concentration of Mn³⁺/Mn⁴⁺ion pair in the thin film.At the same time,Cu⁺can directly exchange electrons with Mn³⁺and Mn⁴⁺at B site.The two mechanisms together reduce the resistance of the thin film.However,Cu⁺is unstable,and it is easy to be oxidized to Cu²⁺under300?,so it will make the aging properties of the thin film worse.Finally,in order to improve the aging properties of Mn_1.46Co_0.86Ni_0.48Cu_0.2O₄ thin film,Mn_1.36Co_0.86Ni_0.48Cu_0.2Ca_0.1O₄ thin film was prepared by doping Ca element.The results show that the co-doping of Ca and Cu can improve the aging properties of the thin film while maintaining the low room temperature resistance and high thermal constant of the thin film.XPS analysis shows that Ca element exists in the form of+2 valence,and Ca²⁺occupies the A site of the spinel structure prior than Cu²⁺.The thermal stability of the CaMn₂O₄ structure is better,so the aging properties of the thin film can be improved.The preparation process is the annealing temperature of 750?,the holding time of 120min,and the cooling rate of 5?/min.The prepared Mn_1.36Co_0.86Ni_0.48Cu_0.2Ca_0.1O₄ thin film has excellent comprehensive properties,its room temperature resistance R₂₅=52.3k?,the heat sensitivity constant B_25/50=3182K,and the aging rate?R/R=3.66%.