| Positive Temperature Coefficient (PTC) materials are temperature sensitive electric materials. The electric resistivity of the material goes up with the temperature increasing. Compared with traditional PTC ceramic materials, PTC metal film thermistor possesses many advantages such as extreme low resistance, fast heat up, high safety factor, long working life, no noise, little power attenuation, high mechanical strength, high flexibility and good sealing properties. PTC metal film thermistor can be used for thermal heaters, temperature sensors and infrared detector.In this paper, the design and preparation of the metal film has been studied. The nickel and iron were selected to be original material. A multilayer structure metal film has been schemed out. This structure enhanced the interface between the films and formed nickel-iron alloy layer, thus largely increasing the temperature coefficient of the resistance. The multilayer nickel iron film has been prepared by vacuum evaporation process which utilized different metal melting point and rotary evaporation source. The temperature coefficient of metal film resistance has been tested by oven, thermometer, multimeter and high temperature wire.The layer number, proportion of metal and temperature of heat treatment on the PTC effect of metal film has been studied. When the quality ratio of nickel and iron was 7:3, the temperature coefficient of resistance of the film sample was maximal 4928ppm/℃. It is summarized that the 12-layer nichel-iron film with the quality ratio 7:3, which was heated at 400℃for 2hours with the heating rate 50℃/s, processes largest temperature coefficient of resistance, 5582ppm/℃.The resistance at room temperature was 301Ω. The non-linear error was 28.2%. |
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