Analytical study of resistive MEM gas flow meters

An analytical study for micro-electro mechanical system (MEMS) type gas flow meters is presented. A bulk micromachined structure for the flow meter is proposed. It consists of a micro resistive heater and two temperature sensors situated at the opposite sides of the heater. The silicon substrate is considered to be thermally isolated from the heater by a stacked (SiO₂/Si₃N₄) membrane on a bulk micromachined cavity. The flow meter is considered to work on the bases of displacement of temperature profile around the heating element due to the gas flow. The obtained equation from the analytical model is applied to a specific device dimension. The calculated results show a linear relationship between the gas flow velocity and the device response when the heater and sensing elements separation is about 80 μm. The linearity decreases for increased separation between the heater and the sensing elements as well as the gas flow velocity. The proposed device is also simulated by finite element method using Ansys/Flotran software. The simulation results are in a good agreement with the analytical results. Our analytical results can assist the MEMS gas flow meter designers to define the position of the sensing elements with respect to the heater accurately, depending on the required output signal linearity and gas flow velocity.