A novel capacitive micromachined transducer for micro-pressure measurement

Abstract

A novel capacitive micromachined transducer is dementrated for micro-pressure measurement. This transducer employs two deflectable diaphragms (the top and middle diaphragms) suspended over a fixed bottom electrode. The two deflectable diaphragms form a mechanical amplifier when a DC bias voltage is applied across them. A change in the deflection of the top diaphragm under the applied pressure is coupled into an amplified deflection change of the middle diaphragm, resulting in a significant resonant frequency shift. Therefore, the transducer can achieve improved pressure sensitivity. The finite element method (FEM) model was established to study the performance. The results show that the pressure sensitivity reaches up to -2.54 ppm/Pa (7.46Hz/Pa) under the bias voltage U bias equal to 95% of the pull-in voltage of the transducer. The nonlinearity error is as low as 1×10 -4 %. A study on the effect of the bias voltage on pressure sensitivity shows the pressure sensitivity increases with the bias voltage. Additionally, as the middle diaphragm is set in vacuum, the air damping effects can be eliminated, thus the transducer performance will be further enhanced. Keywords-Capacitive micromachined transducer; Micro pressure measurement; Michanical amplifier; Resonant frequency shift; FEM modelI.