A hot-film air flow sensor for elevated temperatures

A hot-film air flow sensor for elevated temperatures

We report a novel packaging and experimental technique for characterizing thermal flow sensors at high temperatures. This paper first reports the fabrication of 3C-SiC (silicon carbide) on a glass substrate via anodic bonding, followed by the investigation of thermoresistive and Joule heating effects in the 3C-SiC nano-thin film heater. The high thermal coefficient of resistance of approximately −20 720 ppm/K at ambient temperature and −9287 ppm/K at 200 °C suggests the potential use of silicon carbide for thermal sensing applications in harsh environments. During the Joule heating test, a high-temperature epoxy and a brass metal sheet were utilized to establish the electric conduction between the metal electrodes and SiC heater inside a temperature oven. In addition, the metal wires from the sensor to the external circuitry were protected by a fiberglass insulating sheath to avoid short circuit. The Joule heating test ensured the stability of mechanical and Ohmic contacts at elevated temperatures. Using a hot-wire anemometer as a reference flow sensor, calibration tests were performed at 25 °C, 35 °C, and 45 °C. Then, the SiC hot-film sensor was characterized for a range of low air flow velocity, indicating a sensitivity of 5 mm−1 s. The air flow was established by driving a metal propeller connected to a DC motor and controlled by a microcontroller. The materials, metallization, and interconnects used in our flow sensor were robust and survived temperatures of around 200 °C

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Rev. Sci. Instrum. 90, 015007 (2019) and may be found at https://doi.org/10.1063/1.5065420