Bidirectional CMOS-MEMS Airflow Sensor with Sub-mW Power Consumption and High Sensitivity

This article presents a bidirectional thermoresistive micro calorimetric flow (TMCF) sensor implemented by a 0.18-μm complementary metal-oxide-semiconductor microelectromechanical systems (CMOS-MEMS) technology, while the sensor thickness is thinned to 2.7 μm through an in-house developed MEMS fabrication process. For the bidirectional airflow of -6 to 6 m/s, the TMCF sensor achieves the highest sensitivity of 453 mV/(m/s), and its highest normalized sensitivity with respect to the signal amplification gain (gain = 250) and the input heating power (1.58-1.72 mW) is 1150 mV/(m/s)/W. By reducing the heating power to the sub-mW of <220 μW, the TMCF sensor can still give a remarkable sensitivity of 87.4 mV/(m/s). In addition, the developed TMCF sensor has an intrinsic minimum detectable flow velocity of 99 μm/s and a response time of 4.8 ms. The performance achieved by this flow sensor enables accurate indoor airflow measurements even when dealing with the extremely low-speed flow (<0.05 m/s). Furthermore, the high-performance TMCF sensor is applied for remote human motion detection, where different walking speeds and moving patterns of the occupants can be captured. Therefore, this developed CMOS-MEMS sensor will not only be a promising flow sensing node in the HVAC system, but also potentially be used for the nonvisible and private occupant counting in buildings/rooms.