Abstract
The four-terminal piezoresistive transducer (the Xducer), originally developed by Motorola SPS Inc., has been widely used in place of the more conventional Wheatstone bridge arrangement in diaphragm pressure sensors. A salient feature of the Xducer is that its one-resistor design eliminates the difficult requirement of closely matching the characteristics of the four resistors in the bridge. In this article, we present numerical investigations using the coupled piezoresistive-mechanical module of the MEMCAD4.0 system to aid in optimizing the design and performance of the Xducer. Results indicate that the optimal position for maximum sensitivity is achieved when the resistor center is not at the point of maximum stress, which occurs outside the sensor diaphragm edge, but rather on the sensor diaphragm near the edge. Moreover, as the resistor dimensions are enlarged, the optimal position shifts away from the edge. Furthermore, the misalignment of the resistor from the 45° line, has rather interesting effects. It results in a non-symmetric drop in output voltage despite symmetric deviations around the 45° line.
