Measurement system for wide-range flow evaluation and thermal characterization of MEMS-based thermoresistive flow-rate sensors

Abstract

An optimized design of an analog circuit for measuring the parameters of a MEMS (micro-electro-mechanical system)-based thermoresistive flow-rate sensor is proposed, which combines both calorimetric and anemometric flow measurement modes. Fixing the sensor on a plastic wing tilted at a non-zero angle relative to the direction of gas flow in such a system makes it possible to measure the gas flow velocity in a wide range from 0.05 to 5 m/s with an error of 3 % and a relative standard deviation of 2 %. The use in the proposed circuit of platinum thermistors located on a thin-film dielectric membrane (SiO2/Si3N4/SiO2/Si3N4), which can serve both as heaters and sensitive resistors for temperature measurement increasing the output voltage by an order of magnitude, thereby reducing the noise that occurs when a weak signal is amplified. It has been experimentally shown that the calorimetric method is more suitable for measuring low flow velocities (from 0 to 1 m/s), while the anemometric one is better applicable for detecting higher flow velocities (more than 1 m/s). The rise in temperature of thermistors due to its Joule heating by direct current was measured both in air and in vacuum in the absence of the gas flow. It was found in the experiment that the in-plane thermal conductivity of the four-layer dielectric membrane used in the sensor varies from 2.61 W/(m∙K) to the level of about 3.03 W/(m∙K) with an increase in the heating power in the range from 0.6 to 4 W, respectively.