Development of a robust 2-D thermal wind sensor using glass reflow process for low power applications

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In this paper, a low-power MEMS two-dimensional (2-D) thermal wind sensor with high reliability is presented. The sensor is based on a glass-in-silicon reflow process. The embedded vertical silicon vias in the glass substrate are used to realize the electrical connections between the sensing elements and the electrode-pads, which are respectively placed on on the front and the back surface of the chip. Then, the sensor and the external circuit are connected using the wire-bonding process through the electrode-pads on the back surface. At last, the bonding wires at the backside is encapsulated by polyester paint, protecting the electrical connections of the sensor from the effect of the external environment. In addition, a passivation layer of nitride is deposited on the surface of the wind sensor to prevent direct exposure of the sensing elements to harsh media. The sensor works in a self-heated mode, which makes its power consumption could be reduced into the sub-milliwatt range, offering high initial sensitivity and wide measurement range, respectively. The sensor was tested in a wind tunnel in constant voltage mode. Measurement results show that the thermal wind sensor can measure wind speeds up to 17.5 m/s with a low power consumption of only 4.81 mW. Measurement results also show that wind direction in a full range of 360° with an error within 6° could be obtained.