Characterization of a highly sensitive ultra-thin piezoresistive silicon cantilever probe and its application in gas flow velocity sensing

We present a highly sensitive ultra-thin micromachined silicon cantilever beam with an integrated strain gauge on its root for optimizing piezoresistive readout. The mechanical characteristics and electrical readout of the cantilever beam, such as spring constant, resonant frequencies and piezoresistive sensitivity, are theoretically given from the derived formulae or from finite element modeling. The results of characterization show reasonably good agreement between the experimental results and the theoretical values. As one of the applications, for the first time the fabricated silicon cantilever beams have been applied to measure airflow velocity distribution in a steel pipe with an inner diameter of 7.0 mm. The experimental piezoresistive sensitivity (ΔR/R)/y(0) is in the range of 0.23–2.89 × 10⁻⁶ nm⁻¹ in the beam bending tests, and the experimental flow sensitivity (ΔR/R)/V_gas² is in the range of 0.652–4.489 × 10⁻⁵ (m s⁻¹)⁻² in the airflow velocity tests. The experimental detectable minimum airflow velocity is 7.0 cm s⁻¹, which is comparable to that of a hot wire anemometer.