Characterization of Novel Chip Temperature-Sensing Device Using Mn-Substituted Li–Zn–Cu Ferrite

It has been very difficult to develop a miniaturized temperature sensor device using the conventional temperature-sensitive ferrites, such as Mn-Zn ferrite, which is due to difficulty of the high-frequency operation, because of their low natural resonance frequency (below 1 MHz) and low electrical resistivity (around 10
²
-10
⁴
Omegamiddot cm). The authors have recently developed a polycrystalline Mn-substituted Li-Zn-Cu ferrite with a high natural resonance frequency beyond 10 MHz and high resistivity over 10
⁶
Omegamiddot cm, which exhibited strong temperature-dependent magnetic properties. It was considered that the transmission-line device using a new temperature-sensitive ferrite as an electromagnetic-field propagation substrate enables us to obtain a novel chip temperature-sensing micro device, because of the possibility of high-frequency operation due to a high resonance frequency and high resistivity of the new ferrite. We have simulated a quarter-wavelength resonator using the Mn-substituted Li-Zn-Cu ferrite substrate and its temperature-dependent properties. Since the quarter-wavelength transmission-line resonator includes distributed inductance and capacitance depending on the temperature-sensitive electromagnetic property of the ferrite substrate, this type of device operates as an integrated LC resonator-type temperature sensor. In this study, the integrated resonator-type temperature sensor using a spiral strip-line structure with the Mn-substituted Li-Zn-Cu ferrite substrate was fabricated, and its temperature-dependent characteristics were evaluated.