Development of a High Resolution CMOS Flow Sensor

Based on the standard CMOS process and the post- CMOS micromachining processes, an integrated flow sensor with comprising micro structures and mixed signal processor in 2 mm square chip die size was developed in this study. The sensor microstructures consist of a polysilicon micro heater and the thermopiles array. The central micro heater encircled by the temperature sensors generates the thermal plume. As the sensor is positioned against the flow, the thermal plume is pushed toward to the temperature sensors array and the temperature differences can be converted into the voltage to determine the air flow speed. The surrounding temperature sensors array gives output voltages in x-direction and y-direction. Both flow velocity and direction can be determined with the 0.7 mV/ m/s sensitivity and 0.001 m/s resolution upon the impinge flow ranging from 0.1 to 3.6 m/s. The flow sensor is employed to monitor the flow condition of the thermal module for desktop PC due to the high resolution in low speed air flow field and the sensitive warning to the poor air flow can be achieved by the proposed sensor.