SYNTHESIS AND ELECTRICAL CHARACTERIZATION OF NTC CERAMIC MATERIAL FOR TEMPERATURE SENSOR APPLICATION

Abstract

In our everyday life, the measurement, monitoring and control of temperature is of utmost importance. For this purpose, temperature sensors are used in various domestic as well as industrial applications. Various temperature sensors work according to different applications from which NTC thermistors are of great importance. A negative temperature coefficient (NTC) thermistor material basically shows semiconducting properties which have many applications in the field of electronics, automobiles, healthcare, aerospace, optoelectronics and instrumentation etc. They are widely used in temperature measurements and its control along within the circuits which are used for the suppression of electric current and temperature compensation of other circuit elements of various microelectronic circuits 11-31. NTC thermistors also find their application in the measurement of low volume liquid flow and gas flow. Nickel Manganite based spinals are mostly used For this purpose as they are cheap in cost and easy to manufacture with good thermistor properties. In sensor technologies, ceramics are very useful crystalline materials because of their structural strength, thermal stability, light weight, resistance to many chemicals, ability to bond with other materials, and excellent electrical properties [4]. Some of the transition metals whose oxides are used for this purpose are Mn, Co, Ni etc. The reason For choosing the above transition metals is because of their low room temperature resistivity and good thermistor characteristics. 'l'hcy can also be used for high resistance to magnetic field induced errors and for the ionization of the radiation at low temperature [5]. The nature of these thermistor materials shows a decrease in its resistance with an increase in its body temperature. This characteristic is generally shown by Arrhcnius Plot which clearly reveals the exponential decrease in the values of resistance/resistivity of the NTC thermistor material with a continuous increment in the temperature of the environment where the NTC thermistor material has been kept. The Arrhenius equation is generally given by: p = Po exp (B/T) where Po is the electrical resistivity at infinite temperature, T is the absolute temperature, B is the material/thermistor constant having the formula (B = Ea/kE3), in which E is the activation energy for electrical conduction and kB is the Boltzmann constant. The negative temperature coefficient (NTC) thermistor materials with moderate resistivity (p) and low thermistor constant (B) are very well used for low temperature sensing applications. The graph showing NTC/PTC Characteristics is shown below: