A micromachined single-crystal silicon flow sensor with a cantilever paddle

A series of micro flow sensors with cantilever paddles are developed which are based on the detection of surface strain on the cantilever caused by the mass flow. The sensing structure is a 10-/spl mu/m thick single crystal silicon cantilever beam attaching a square paddle. In measuring, the flow causes a deflection on the cantilever which is proportional to the volume flow rate, then the strain is detected by the piezoresistance bridge integrated on the supporting root of the beam. The size of the sensing chip is 3.5 mm/spl times/3.5 mm. The packaged sensor is /spl Phi/ 10 mm/spl times/4 mm in size, with two /spl Phi/ 2 mm/spl times/25 mm inlet and outlet fluid tubes. The sensors with different detecting structures achieve different measuring ranges. The lowest theoretically detectable flow rate is 100 /spl mu/l/min for water, and 5 ml/min for air. Testing of the fabricated sensors shows an acceptable linearity of /spl plusmn/5% under an air flow rate of 10 ml/min to 200 ml/min.