Behavior of bulk micromachined silicon flow sensor in the negative differential resistance regime

The performance of a bulk micromachined silicon flow sensor in the negative differential resistance (NDR) regime is investigated for air flow measurements. The NDR regime of operation is obtained by boosting the pulse height in typical pulse mode operation. Our measurements show that operation in the NDR regime results in increased sensitivity compared to operation in the saturation regime. The increased sensitivity in this regime occurs at relatively higher temperatures with a possible increase in power consumption. In the pulse mode of operation, with a 3 mA, 100 ms pulse, the unamplified linear sensitivity is 40 mVs m exp -1 for the flow velocities in the range of 5.3-21.0 m s exp -1 . In the NDR regime with a 6 mA, 100 ms pulse, the latter is 67 mVs m exp -1 for the same flow velocity range. In addition, driving the sensor into the NDR regime results in a response curve (impulse shaped) which shows the potential use of different parts of the pulse response to ascertain flow information. Furthermore, for the first time, we report here the pulse type output voltage made possible in the NDR regime for a continuous current input to the sensor.