Analysis and stability of a silicon-based thermally actuated MEMS viscosity sensor

Abstract

The proposed MEMS-technology viscosity sensor solves two major drawbacks associated with current state of the art MEMS viscosity sensors, such as: (1) Functional complexity and integration of external components for actuation and subsequent data acquisition; (2) Fabrication incompatibilities with CMOS processes. The proposed solution is based on thermally induced actuation, subsequent vibrations of a silicon plate, and, plate damping in the surrounding fluid. This vibration viscometer device utilizes thermal actuation through an in-situ resistive heater and piezoresistive sensing of vibration. The studied MEMS sensor structures and components utilize CMOS compatible materials and fabrication processes. This leads to affordable, high-yield and reliable systems. A technology-centric solution is verified, tested and characterized to demonstrate that sensor is capable of measuring viscosities in the range from 10 to 500 cP with less than 5% error. Long-term stability testing shows a frequency variation of less than 5% for more than 1×106 actuation cycles.