Thin and Thick Film Ceramic-Based Passive Wireless Temperature Sensors for Harsh Environments
Authors: Sivaneri Varadharajan Idhaiam Kavin , Jones Kodey , Naidu Gautam , Sabolsky Katarzyna , Sabolsky Edward M. , Comparetto Michael , Reynolds Daryl S. 
Published: February 2020

The needs for real-time temperature monitoring of energy systems in extreme conditions keeps increasing due to the growth of manufacturing industries. Current technologies utilize thermocouples, infrared laser interferometers, and surface acoustic wave (SAW) sensors. Thermocouples have limited lifespan. The reliability is poor due to continuous redox reaction taking place at the hot junction and any caustic environment will corrode the thermocouple material. Laser interferometers are limited by the spot area of the laser beam and monitoring temperature gradient is difficult, since it is a surface sensitive technique. To overcome the limitations, research has been focused on passive wireless sensor technology where an inductor–capacitor (LC) circuit was used to monitor the temperature and local strain conditions.

The primary objective of this work was to study the materials properties of carbide/silicide and oxide composites for the fabrication of ceramic-based LC circuits on a ceramic substrate using thin and thick film deposition methods. This work includes the investigation of the composite precursor, pattern technology and the effect of thermal processing on the final pattern and stability. The relation of volume shrinkage during sintering process and phase development are of interest. The secondary objective of this work was to investigate the electrical properties of the tailored sintered electrodes. One system that will be discussed is the development of a polymer-derived electroceramic electrodes based on two different carbide/silicide compositions. These inks were synthesized by mixing a siloxane/silane compound with an active inorganic filler material. Upon sintering, the organic molecules decomposed and the silicon will react with the inorganic fill at a higher temperature to form a ceramic composite. The reaction kinetics depends on the reaction between terminating functional groups, silicon ``atom, and the filler particle. To understand the reaction kinetics, phase formation, and other mechanical properties (such as volumetric shrinkage), varying ratios of the particle filled polymer matrix was injection molded and sintered at varying temperature rates. The compositions that provided the desired material properties was chosen to direct-write the LC circuit pattern on a ceramic substrate by a 2D printing technology and screen printing technology. The sintered sensor was characterized by XRD, SEM and the electrical characterization of the printed LC circuits were completed on the sensor compositions by a signal analyzer in tandem with an oscilloscope (at temperatures 50-1300oC).

Miniaturization of the LC circuit was developed by a thin film deposition process to show the effect of size reduction in various aspects of sensing and adaptability. Miniaturized LC circuit was patterned by depositing by physical vapor deposition onto a ceramic substrate. Additionally, the size reduction will boost the capacitance of the circuit which will assist in the reduction of the signal-to-noise ratio, ease of signal processing and reduces the sophistication of electronics. The fabricated thin films were characterized by grazing incident XRD and SEM to compare the formation of grain boundaries, phases with the thick film composite. The electrical characterization was completed in a similar fashion to compare results with thick film composites.