Effects Of Composition And Thermal Treatment To NTC Thermistor Components

Negative temperature coefficient resistor(NTCR) has the character that its electrical resistance exponential decreases with increasing temperature. Because its advantage such as high accuracy, high sensitivity, low cost, and high signal to noise ratio, it has been widely used in almost every field like home appliances, manufacturing industries, precise instrument, etc, as temperature sensors, temperature control and compensation devices, voltage and current stabilizers, has a large market. NTCR includes ceramic NTCR, thick film NTCR and thin film NTCR. To compare with ceramic and thick film NTCR, thin film NTCR has higher accuracy, higher sensitivity and smaller size, meets the tendency of miniaturization and integration, attracting more and more attentions. Main purpose in this paper is to control the NTC thermistor element`s main parameters : B value and the room temperature resistivity r25, study the influence of components regulation, doping, ceramic sintering temperature on microstructure and NTC resistance properties of Mn-Ni-O, Mn-Co-O system oxide spinel structure NTC material and the influence of annealing process on amorphous magnetron sputtering NTC thin film.In this paper, we prepared Mn-Ni-O, Mn-Co-O based NTC resistance material by using solid phase syntheses, studied the effect of wide range proportion of elements and element doping on performance of the material.The results show that with the increase of Ni content, Mn-Ni-O system`s B value basically remains unchanged, and the resistivity increases dramatically; the system`s B value and the room temperature resistivity decrease sharply with the doping of Cu, and Cu doping also improves the sintering properties of the Mn-Ni-O material. For Mn-Co-O system, the B value and r25 decreases first and then increases with the increase of Co content, the system`s B value and r25 decreases sharply withthe doping of Cu; Doping Si makes a dramatic rise in r25 and B value basiclly remains unchanged.Spinel structure oxide NTC material has polaron hopping conductivity mechanism, therefore B value and r25 have a strong correlation, they often change at the same time.Considering the demand of precise adjusting of B value and r25 simultaneously, especially for low B value, high r25 NTC material, this paper studied the influence of sintering temperature on the properties of ceramic materials base on Mn-Co-O NTC resistance. Experimental results show that, for Mn1.55Co1.45O4 NTC resistance material, at the range of 1200°C ± 50°C, with the increase of sintering temperature, and B value basically remains unchanged, the room temperature resistivity decreases by 34%;And for Mn0.9Co2.1O4 NTC resistance, with the increase of sintering temperature, B value basically remains unchanged, the room temperature resistivity increases by 43.5%.Therefore, it is a very effective way to adjust the NTC ceramic resistance parameters by controlling the sintering temperature.The amorphous magnetron sputtering NTC thin film crystallizes in the process of high temperature annealing, results in electric properties and morphology change.In this paper, we used Mn-Co-Ni-O function layer- Al N substrate NTC film, studied the influence of different annealing processes on the properties and morphology of NTC film. The situ resistance test results of annealing process show that at 450 °C, the amorphous NTC film resistance changes obviously, and goes through the process of structure relaxation, crystal taxiing and grain growth. At constant temperature annealing stage, because of the different type of chemical bond between Al N substrate and function layer, crystallize contractionl results in the increase of function layer`s porosity, so the resistance increases; The higher the annealing constant temperature, the faster resistance increase, and the higher B value is of NTC thin film after annealing; Constant temperature annealing time has little effect on B value, while with the extension of annealing time, the resistance of NTC film increases. Because the thermal expansion coefficient of Mn-Co-Ni-O function layer and Al N substrate is different, and the associative property is bad, when annealing temperature is higher than 800 °C, functional layers separates from substrate and forms bubbles, so the annealing temperature should be controlled under 800 °C.