Effect of packaging asymmetry on the performance of a 2D MEMS thermal wind sensor with different heating geometries

In this paper, the effect of packaging asymmetry on the performance of a 2D MEMS thermal wind sensor with different heating geometries is investigated quantitatively for the first time. The thermal wind sensor is fabricated on a silicon-in-glass (SIG) substrate with anisotropic thermal conductivity by a lift-off process. The silicon vias embed in the glass are employed to exchange heat between the device and the airflow, whereas the glass is used to reduce the invalid heat loss and improve the sensitivity of the sensor chip. In the experiment, the wind sensor was operated by using different heating geometries, which are respectively annular heating geometry, square heating geometry and hybrid heating geometry. Measurement results show that, with different heating geometries (annular, square and hybrid), the mean square errors of the output voltage versus wind direction (0-360 degrees) of the sensor at 30 m/s are respectively 5 mV, 25 mV and 11.67 mV before compensation. The corresponding average direction errors of the sensor are respectively 3.42, 11 and 5.79 degrees. It can be seen that the thermal wind sensor with annular heater geometry is less susceptible to package errors.