Basic investigation of microtemperature sensor by means of a novel transmission-line technique using a temperature-sensitive Li–Zn–Cu ferrite substrate

Abstract The polycrystalline Mn-substituted Li–Zn–Cu ferrite exhibits a very strong temperature dependence of magnetic properties, high natural resonance frequency, and high resistivity. The authors carried out the basic investigations of the temperature sensor using this new temperature-sensitive ferrite. As the first step, the temperature-sensitive LC resonance circuit using the Li–Zn–Cu ferrite chip inductor was fabricated, and the temperature dependence of its input impedance was evaluated. The resonance frequency was decreased linearly with a large temperature coefficient. Furthermore, it was also found that the input impedance in a constant frequency operation indicated extremely temperature dependence. In order to integrate and miniaturize the temperature sensing device, a possibility of the integrated temperature-sensitive LC circuit by means of the transmission-line technique was investigated. For our motivation, the monolithic integrated temperature sensor using spiral strip-line with Li–Zn–Cu ferrite substrates, which has the temperature dependent magnetic property, was simulated by the electromagnetic field and the equivalent circuit analysis. It was clarified that the monolithic sensor exhibited remarkable temperature dependent input impedance as well as the temperature-sensitive LC resonance circuit.