A hot-film air flow sensor for elevated temperatures

Abstract

We report for a novel packaging and experimental technique to characterize thermal flow sensors at high temperatures. To start with, the paper briefly presents the fabrication of 3C-SiC (silicon carbide) on a glass substrate via anodic bonding, followed by the study of thermoresistive and Joule heating effects in the 3C-SiC nano-thin film heater. A high thermal coefficient of resistance (TCR) of approximately-20,720 ppm/K at ambient temperature and-9,287 ppm/K at 200°C suggest 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 the SiC heater inside a temperature oven. In addition, the metal wires from the sensor to external circuitry were protected by a fibre glass insulating sheath to avoid short-circuit. The Joule heating test ensured the mechanical and Ohmic contact stabilities at elevated temperatures. Using a hot-wire anemometer as reference flow sensor, calibration test was performed at 25°C, 35°C and 45°C in the oven. Finally, 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.

Microfluidic thermal flow sensor based on phase-change material with ultra-high thermal sensitivity

“…2c shows the comparison of TCR values for VO 2 and other temperature-sensitive materials, where the maximum α v ( T ) in the IMT region shows values more than 60 times higher than conventional metallic thermal sensing materials, such as Pt, 2 which is the material used as the sensing element in most microfluidic thermal flow sensors. It should be noted that although the ultra-high α v ( T ) can only be obtained in a small temperature window, the room temperature α v ( T ) still maintains at a high value of −0.024 K −1 , which is comparable to the recently proposed cubic silicon carbide (3C-SiC) 10 and single-walled carbon nanotubes (SWCNTs), 6 and still 6 times higher than Pt.…”

“…7 By subsequently implementing focused ion beam (FIB), wet etching, and annealing processes, 8 silicon NWs (SiNWs) has demonstrated a high negative TCR of −12 000 ppm K −1 . Recently, cubic silicon carbide (3C-SiC) has been introduced for air flow sensing at elevated temperatures, 9,10 the TCR is found to be −20 720 ppm K −1 at ambient temperature and −9287 ppm K −1 at 200 °C, which is about one order of magnitude higher than Au. These advances in high TCR materials successfully eliminate the use of suspended structures while maintaining the high sensitivity.…”

Silicon monolithic microflow sensors: a review

“…No data [23] Hot-wire No data [31] (Continued.) No data [32] Thermistor-based No data [33,34] Thermistor-based…”

Piezoresistive Effect with a Gauge Factor of 18 000 in a Semiconductor Heterojunction Modulated by Bonded Light-Emitting Diodes

“…The piezoresistive effect is one of the dominant effects utilized in micro/nanoelectronic sensors besides thermal resistive effect, − piezoelectric effect, and photovoltaic effect . The piezoresistive effect is a main sensing effect in micro/nanoelectromechanical systems (MEMS/NEMS).…”