Design, Fabrication, and Testing of the Van Der Pauw Piezoresistive Structure for Pressure Sensing

In our specific application of the van der Pauw (VDP) structure as a pressure sensor, where the stress field varies significantly, smaller VDP size is beneficial. The resistivity of the VDP sensor is affected by the stress state of the entire area over which it lies, providing a relation between resistance and the average stress in an area, rather than the stress at a point. The further the area over which the VDP lies is reduced, the closer we approximate the stress at a point rather than the average stress over a large surface. Due to microfabrication and other limitations, small, point-like sensors may not be feasible. In our study, a clear relationship between size and sensitivity could not be made. However, it was apparent that size had little overall effect on sensitivity. In testing the VDP devices for comparison with conventional sensor types, it was found that the VDP devices had a linear response as expected, were the most sensitive, and provided a number of additional advantages. Specifically, the VDP device allows for significant miniaturization, because its resistance value is independent of size, and the measurement technique is independent of line resistance. The simple geometry of the VDP also simplifies fabrication.