A MEMS-based hot-film thermal anemometer with wide dynamic measurement range

This paper describes the fabrication and characterisation of a micromachined thermal flow sensor based on platinum thin film resistors. The spatial design and geometric dimensions of the sensing elements result in a very short response time of less than 1 ms and in a very wide measurement range of flow velocities from below 1 m/s up to 180 m/s with a high sensitivity of 72 mV/slm at low flow rates and an acceptable sensitivity of 7.34 mV/slm even at high flow velocities. The heater power was varied from 4.4 to 34.9 mW. The same platinum-resistor is used for heating and sensing and an additional resistor is used for temperature compensation. Geometrically identical resistors were fabricated on silicon wafers as well as on flexible glass substrates and were tested in an air flow. The measured temperature coefficient of resistance (TCR) of the platinum resistor is 0.0027 K^-1. A constant temperature anemometer (CTA) setup is used to measure the air flow velocity.