Sensitivity Analysis of Planar Piezoresistive Sensors for MEMS Applications

In this study, the sensitivity of two-dimensional four-terminal piezoresistive sensors commonly referred to as “van der Pauw (VDP)” structure is investigated and analyzed. VDP sensors have the potential to obviate some of the limitations of resistor based sensors such as size and temperature effects. In this study, we will consider the VDP sensor to be fabricated on (100) silicon due to its potential application in MEMS pressure sensors or electronic packaging stress measurements. The sensitivity of the VDP sensor may be affected by misalignment (i.e., orientation) during the etching/diffusion process, the size of the sensor relative to the size of the underlying diaphragm, pad size where the current and voltage are determined, and on their global positions. In this study, we have presented how the VDP stress sensitivity is affected by variations in pad size and sensor orientation with respect to the wafer flat direction. First, a 3D finite element analysis (FEA) model is developed representing a piezoresistive VDP sensor fabricated on (100) silicon diaphragm. Then, the FEA model is validated with the closed form analytical solution for different bi-axial loads. Once the FEA model is validated, additional simulations are conducted to understand the influence of different parameters on the resistance measurements. The change in resistivity of the VDP will then be analyzed to predict its sensitivity under a certain set of sensor parameters.