Behavior of bulk micromachined silicon flow sensor in the negativedifferential resistance regime

Abstract

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