A novel micromachined viscosity and density sensor based on resonant torsional paddle

A micromachined resonant torsional paddle is presented to sense the viscosity and density of the liquid. The paddle is designed to work with torsional vibrating mode to improve the sensitivity. To simplify the fabrication, low-stressed SiNxwith 5 um in thickness is used as the paddle. A positive-feedback circuitry is used to compensate the energy loss by the big damp in liquid, so that the SNR and the Q-factor of the paddle can be improved obviously. Characteristics experiments show that the Q-factor of the paddle in alcohol is enhanced from 2.65 to 24.55, and the torsional resonant frequency and the Q-factor of the paddle decrease with the density and the viscosity of the mixture solution respectively.