Out-of-plane micro triple-hot-wire anemometer based on Pyrex bubble for airflow sensing

The paper reports novel design and fabrication of out-of-plane micro airflow sensors based on the hot-wire sensing principle, i.e. gas cooling of electrically-heated wires. Three micro Ti/Au/Cu hot-wire resistors have been fabricated on an out-of-plane Pyrex bubble with height of 300 μm. They are arranged 120 degrees apart on the sidewall of a bubble at height of 100 μm for airflow velocity and direction detection. Air velocity around the out-of-plane bubble structure has been investigated for square and circular package designs. The sensor with axisymmetric circular package has demonstrated the ability to detect velocity (<10 m/s) and to determine flow direction with an error less than ±8° when the velocity is 10m/s. The sensitivity could be further improved in a new design with increased bubble height (1 mm) and elevated hot-wire resistor position (500 μm), according to the modeling results.