Computational investigation of van der Pauw structures for MEMS pressure sensors

This research aims at replacing the conventional filament type resistor piezoresistive sensor with a square conductor with four electrical contacts. The four-contact conductor, popularly known as van der Pauw (VDP) structure, is a test structure widely used for measuring resistivity of arbitrarily shaped samples of constant thickness. Over the years, many researchers have extended the original ideas to develop a variety of approaches for evaluating the resistivities of both isotropic and anisotropic materials using VDP type structures. When used as pressure sensors, VDP devices have the potential to obviate some of the limitations of resistor based sensors. In this paper, finite difference and Finite Element Analysis (FEA) methods have been used to model a square VDP structure under biaxial stress condition. The FEA method was also used to model a serpentine filament resistor. It is observed that the sensitivity of VDP based sensor is more than three times higher than the conventional filament type sensor. In addition, this sensor is seen to have no drift while measuring normalized resistance change difference (NRCD). The sensor is also size independent. Thus, the sensor can be made very small without losing its sensitivity with no drifting issues. As the future applications of MEMS focus on integrating various sensing devices in a small area to reduce weight and cost, an alternative small-size piezotransducer will be beneficial for such future applications.