Micromachined flow sensors using a piezoresistive cantilever paddle

A piezoresistive silicon cantilever paddle for measuring gas flow is presented. The paddle square is attached by two cantilever arms with piezoresistive sensing element implanted on the root of the arms. The cantilever paddle is 500 ¿m long, 40 ¿m wide and 2.32 ¿m thick, with a paddle square of 200 by 200 ¿m. The device resistance change is measured using a Phase Sensitive Detector (PSD) method when the piezoresistor on the device is taken as one of four resistors in ac Wheatstone bridge biased at a voltage of 2.0 V and 10 kHz. The measured airflow velocity is in the range 0 - 22.0 m/sec. The minimum detectable airflow velocity is about 10 cm/sec in our PSD experimental setup. The output signals of the device are in reasonable agreement with the theoretical predictions, which are proportional to the flow velocity squared in the drag measurement mode.