Crystallographic Dependence Research Of The Properties And Electrical Transport Mechanism Of La(Ni)-Mn-O Thermosensitive Thin Films

Negative Temperature Coefficient（NTC）thermal films are used as temperature sensors,which are characterized by an exponential decrease in resistance with increasing temperature.It has the advantages of high temperature sensitivity,small size,fast response,low price,and good integration.Therefore,it is widely used for temperature measurement,temperature compensation and temperature control.Transition metal oxides with spinel（AB₂O₄）chalcogenide structure（ABO₃）are most commenly used NTC thermistor ceramic systems.In recent years,there have been many studies on exploring the behavior of NTCs in novel materials for thermistor applications.The ideal crystalline atomic arrangement has a periodic nature,called long-range order.Amorphous materials do not have periodic atomic arrangements and do not have a long distance order,but the atomic arrangements in amorphous materials still retain a short range order of atomic arrangements.Compared to the crystalline state,the amorphous semiconductors have a large number of defects,and they have an important effect on the electrical properties of amorphous semiconductors.While traditional crystalline metal oxides have been relatively widely studied and applied,some metal oxides have equally excellent properties in the amorphous state.Amorphous materials are commonly found in the field of emerging semiconductor devices.The electrical properties and functionality of these devices are often closely related to the operating temperature.Therefore,an in-depth understanding of the temperature-dependent electrical transport in metal oxide amorphous materials is important to optimize the design of these devices.In addition,the understanding of the electrical transport of the semiconducting properties of many amorphous metal oxides remains elusive and the mechanisms of electrical transport have not been fully revealed compared to that of crystalline materials.Therefore,exploring the temperature-dependent electrical transport mechanisms of amorphous metal oxide materials is important for regulating and optimizing the electrical properties of such materials and their applications in areas such as thermoelectric devices,memories and thin-film transistors（TFTs）.The main results of this thesis are as follows:First,polycrystalline La-Mn-O films were prepared by magnetron sputtering,and the effect of substrate temperature on the microscopic morphology of the films was investigated by adjusting the substrate temperature parameters during the sputtering process.At the substrate temperature of 300℃and 350℃,the prepared films can be observed more obvious grains,with the further increase of the substrate temperature to 400℃and 450℃,it is almost impossible to observe the obvious grain boundaries,due to the film and substrate thermal stress causes cracks and a large number of defects on the film surface.Next,the effect of annealing temperature on the temperature-dependent properties of the electrical properties of La-Mn-O films was investigated.After annealing at 550°C-700°C,obvious grains were observed,and a decrease in grain size appeared with increasing annealing temperature.The surface of the La-Mn-O films annealed at 800°C had pores and numerous defects.The electrical properties of the films were analyzed after annealing at different temperatures.The electrical resistance of the film samples decreased as the annealing temperature increased,and the film samples annealed at 600°C had the lowest B values.By changing the annealing process,the crystalline state of La-Mn-O thin film was changed and amorphous La-Mn-O thin film samples were successfully prepared.The effect of crystallization state on the temperature-dependent properties of the electrical properties of La-Mn-O thin films was investigated by comparing the phase structure,microscopic morphology and local chemical states of amorphous and polycrystalline La-Mn-O thin films.The deviation of the electrical transport from the Arrhenius equation in amorphous La-Mn-O thermosensitive thin films is specifically investigated,and the electrical transport mechanism is described.The resistance-temperature curves were fitted in segments,and the deviations were initially analyzed to be caused by the conductive mechanism dominated by the variable-range jump transport at low temperatures and by the thermal activation mechanism at high temperatures.Finally,the amorphous and polycrystalline Ni-Mn-O films were prepared by a tuned magnetron sputtering process,and the electrical transport mechanisms of the two films were investigated.It was found that amorphous Ni-Mn-O films have low roughness and small grain size compared to polycrystalline films.Comparing the chemical states of the ions of the two films,the Mn ions of the polycrystalline Ni-Mn-O film are dominated by Mn⁴⁺and the amorphous Ni-Mn-O film is dominated by Mn³⁺.The polycrystalline Ni-Mn-O films have fewer Mn³⁺ions involved in hopping conduction and higher resistance values than the amorphous Ni-Mn-O films.Unlike polycrystalline Ni-Mn-O thin films,the electrical transport of amorphous Ni-Mn-O thin films deviates from the Arrhenius equation phenomenon,and this phenomenon is analyzed and studied by segmentally fitting the resistance temperature curves,and the electrical transport mechanism changes from a variable range jump mechanism to a thermally activated transport mechanism from low to high temperatures.