Fabrication And Electrical Properties Of The LaMnO₃/Y₂O₃ Bilayer Thin Film Thermistor By Magnetron Sputtering

NTC thermistor has the characteristic that the resistance value decreases with increasing temperature.It has high sensitivity to temperature changes and low price.It is widely used in temperature measurement,temperature control and temperature compensation fields.NTC thermistors are used in a wide temperature range of25-500°C,requiring low B value,high?and excellent stability.Its application areas cover various heating equipment,household appliances and industrial temperature detection.It is an ideal product to replace metal sensors and has a very broad application prospect.Therefore,more and more researchers are conducting research in this area.At present,the research of wide temperature range thermistor materials mainly focuses on single-phase perovskite oxide(ABO₃)and composite materials.However,due to the complex preparation process and harsh sintering conditions,its practical application is limited.Therefore,it is of great significance to explore new NTC materials or structures as a wide temperature range thermistor.LaMnO₃has NTC characteristics,low room temperature resistivity,and low B value,in order to obtain NTC thermistors that can be used in a wider temperature range.This paper will design a double-layer structure of NTC thermistor film,and make the low-resistance phase LaMnO₃and high-resistance phase Y₂O₃into a double-layer structure to obtain a thermistor with high resistance and low B value,which is expected to be applied in wide temperature range.In this paper,LaMnO₃single-layer thermistor film materials,Y₂O₃single-layer thermistor film materials and LaMnO₃/Y₂O₃double-layer thermistor film materials were prepared by DC reactive sputtering.For LaMnO₃single-layer thermistor film materials,by comparing different sputtering powers,different sputtering times and different annealing temperatures,explore the effects of different sputtering conditions on the microscopic morphology,element distribution,and electrical properties of LaMnO₃film materials.Optimal parameters for magnetron sputtering.The effects of different annealing temperatures on the phase structure,microscopic morphology,element composition and temperature resistance characteristics of Y₂O₃single-layer thermistor film materials are studied;for double-layer structure film materials,the effect of different annealing temperatures on the phase structure of double-layer structure film materials is explored.The influence of microscopic morphology,element distribution,and electrical properties,and finally a thermistor double-layer film with high resistance and low B value.Through XRD,SEM,EDS,XPS and other test methods,the phase structure,microscopic morphology,element distribution,and ion valence state of single-layer and double-layer structure films are explored.Through the resistance temperature test,the Hall effect test has carried out the electrical performance research on the film.The main conclusions are as follows:(1)The La-Mn alloy target was sputtered by DC reactive sputtering to prepare LaMnO₃film.By changing the sputtering time,sputtering power and annealing temperature,the optimized parameters of magnetron sputtering were obtained.The resistance value of LaMnO₃thermistor film at 25?90°C decreases with the increase of temperature,showing good negative temperature coefficient characteristics.The EDS surface scan analysis showed that the La-Mn alloy target was sputtered by the DC reactive magnetron sputtering method.After the sample was annealed at 700°C,a ceramic film with approximately the same composition as the target could be obtained.At 25°C,the resistance value of R₂₅decreases from 56.8 to 26.5 k?,and the value of B_25/50decreases from 3864 K to 3347 K.And as the annealing temperature increases,the thickness of the film increases,the oxygen content of the film increases,and the resistance value of the film decreases.After aging at 300°C for 300 h,the annealing temperature is 650,700,750 and 800°C,the aging coefficients are 3.41%,2.48%,2.25%,2.10%,respectively.(2)Using DC reactive sputtering method to sputter Y target to prepare Y₂O₃film.The effects of different annealing temperatures on the phase structure,microscopic morphology and element composition of the film were studied.From the SEM analysis,it can be seen that as the annealing temperature increases,the grain size of the film gradually increases,and the grains grow in columnar form.And the thickness of the film hardly changes with the increase of annealing temperature.It can be seen from the XPS analysis that when the annealing temperature is 650°C,the stoichiometric ratio of the film is closest to Y₂O₃.(3)La-Mn alloy target and Y target are sputtered by DC reactive sputtering method to prepare LaMnO₃/Y₂O₃double-layer structure heat-sensitive film material.From the XRD analysis,it can be seen that the double-layer structured film samples at different annealing temperatures have formed perovskite phase and Y₂O₃phase,and no other impurity phases are formed.From the SEM picture,it can be seen that with the increase of annealing temperature,the grain size of the film of LaMnO₃/Y₂O₃double-layer structure decreases first and then increases,and there are obvious interfaces between the two layers.The LaMnO₃layer adheres well to On the Y₂O₃layer,no cracks were found at the interface.Combined with the EDS line scan,it can be seen that there is no element diffusion between the double layers,indicating that the LaMnO₃/Y₂O₃double-layer structure thermistor film has been successfully prepared.According to the electrical performance test,the conductivity type of the double-layer structure thin-film semiconductor is n-type.When the double-layer film sample is at 25°C,the resistance value R₂₅first increases and then decreases with the increase of annealing temperature,ranging from 13.1 to 3.7 M?,and the B_100/300value increases from 1952 to 2691 K.After aging at 300°C for 300 h,the annealing temperature is 650,700,750 and 800°C,and the aging coefficients are 20.7%,21.9%,18.1%,and 16.9%,respectively.The grain size and the jump conduction of electrons between Mn³⁺and Mn⁴⁺affect the electrical properties of the double-layer structure film.