| Most of the negative temperature coefficient(NTC)thermistors used in practice are based on solid solutions of transition metal oxides with a spinel structure.They are widely used for the suppression of in-rush current,temperature measurements and controls.As an electronic material,the tendency of the development NTC thermistor is to become smaller and thinner.The general film preparation methods include screen printing,pulsed laser deposition,electron-beam evaporation,magnetron sputtering,sol-gel,and hydrothermal technique,while the process of the traditional preparation technique of film is quite complicated from the previous preparation to the post processing,which would have a negative impact on the properties of the film.However,the hydrothermal method for preparing the films ensures that the preparation process can be done at one time in the liquid phase,without annealing or crystallization treatment in the next process,thereby avoiding the grain coarsening,curling and cracking of the films during the process of post treatment,and the unstable properties of the films caused by the reaction of the films with substrate.In this study,nickel manganese spinel films with A1 and Zn cation doping were fabricated via hydrothermal reaction method and the XRD,SEM,SPS,resistance-temperature test techniques were used to investigate the structure and properties of the thermistor films.The main contents are as following:The spinel NTC thin film was fabricated using hydrothermal method.The effect of hydrothermal reaction time(2h?5h?10h and 15h)on the microstructure and electrical properties of the NiMn1.8Al0.2O4 films which were deposited on Al2O3 substrate.The result shows that the microstructural compact films could be obtained at 230 0C for 2 h.Moreover,the grain size increases from 2.5?m to 5.4?m when synthesis time is prolong from 2 h to 15 h,respectively.All the NTC films show good NTC properties.The material constant and activation energy increase with the increase of reaction time,the material constant is 4645 K when the reaction time is 15 h.This study shows that the hydrothermal method is a new method to prepare the NTC thermistor films,and providing technical support for the NTC thermistor films materials by hydrothermal method.In order to create desired electrical property,the addition of Zn for Mn in NiMn1.8-XAl0.2ZnXO(0?x?0.2)NTC thermistor films was attempted using hydrothermal methods.The aim of this work is to understand the effect of Zn content on the microstructure and electrical property of the films.The SEM results show that the microstructure of Zn-doped films is composed two structures,which one is a sheet structure closely related to the substrate,and the other is granular structure on the nano flake,and the size of crystal particles increases with the increase of Zn content.The XPS results show that the Mn2+ content decrease while the Mn+3/Mn+4 increase with the increase of the Zn content and the decrease of the total content of Mn.The electrical study shows that the films show a good NTC characteristic.The room temperature resistance of the films will increase with the increase of the content of Zn,and the material constant is in the range of 4000?4200 K.The resistance of Zn-doped NTC thermistor films is stable after the aging at 150? for 300 h,and the maximum aging rate is 22.2%.The aging study shows that NTC thermistor films with high stability can be obtained through doping Zn. |
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