A CMOS MEMS Thermal Flow Sensor for Gas and Liquid With Parylene-C Coating
Wei Xu, Xiaoyi Wang, Basant Mousa, Maria Paszkiewicz, Yi-Kuen Lee
Abstract
This brief presents a self-heated thermoresistive flow (SHTF) sensor for both gas and liquid with Parylene-C coating using a 0.35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ \mu \text{m}$ </tex-math></inline-formula> CMOS MEMS technology. For N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flow, the developed SHTF sensor can achieve the highest normalized sensitivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S^{ \ast }{ =}\,\, {S}_{c} / {P}$ </tex-math></inline-formula> ) of 171 mV/(m/s)/W with its power consumption <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}$ </tex-math></inline-formula> of less than 18.3 mW. Meanwhile, the SHTF sensor has an accuracy of ±0.04 m/s within the linear flow range of 0–2.5 m/s, which is capable of indoor airflow measurement even in humid environment. For water flow, the SHTF sensor gains a sensitivity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{W} ^{ \ast }$ </tex-math></inline-formula> of 6.42 V/(m/s)/W with the configured calorimetric setup, while its sensitivity increased by more than 4X as it assigned as anemometric for a Nusselt number <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nu</i> of 0–9. Therefore, this highly sensitive CMOS MEMS SHTF sensor with the coated Parylene-C will be a very useful device for both gas and liquid flow measurement in heating, ventilation, and air conditioning (HVAC) and microfluidic applications.