An UHF band planar resonator temperature sensor constructed from high-performance titanium dioxide system microwave dielectric ceramics: Toward integrated ceramic-based sensor devices

With the rapid fusion of temperature sensing technology and microwave technology, microwave temperature sensors have become the protagonist of competing research. We propose a planar resonator temperature sensor that combines substrate material modifications with sensor structure design. To realize this concept, high-performance TiO2-xwt. % ZnO (0 ≤ x ≤ 3) microwave dielectric ceramics are prepared. The various factors influencing dielectric properties, including crystal structure, phase composition, Raman vibration, microstructure, element valence, and oxygen vacancy, are completely investigated. The TiO2-0.7 wt. % ZnO ceramic exhibiting exceptional properties (εr = 106.6, Qf = 46 000 GHz, τf = 426.0 ppm/°C) is selected for substrate fabrication. The frequency and temperature dependence of εr and tan δ are analyzed at 2–4.5 GHz from −50 to 100 °C, revealing a good linearity between εr and temperature. A CSRR temperature sensor employing this substrate material is designed, simulated, fabricated, and validated from −50 to 90 °C. This sensor generates two resonance frequencies (around 0.5 and 1.4 GHz) in the UHF band, demonstrating sensitivities of 2.2 MHz/10 °C and 6.3 MHz/10 °C at the first and second resonance frequencies, along with an outstanding normalized sensitivity of approximately 0.045. Through a comprehensive analysis of the physical mechanisms affecting the sensor's sensitivity and quality factor, the design of the sensor is strengthened from the perspective of optimizing the performance of microwave dielectric ceramics. The regulation mechanism of dielectric characteristics is enriched and clarified, thereby achieving a synergistic improvement in sensor performance. This work expands the application scope of microwave dielectric ceramics and provides an innovative approach to environmental monitoring.