Sensitivity of Van der Pauw sensors to uniaxial stress

Resistor based piezoresistive sensors fabricated on (100) silicon surfaces are capable of measuring four stress components on the surface of a die. Such sensors have been successfully designed and fabricated on test chips that are being used for measurement of die stresses in electronic packages. However, the use of resistor sensors has several drawbacks including their relatively large size, low sensitivity, and limited functional temperature range. Van der Pauw (VDP) structures have been identified as one potential sensor candidate for overcoming the limitations of large resistor sensors. In the current investigation, the piezoresistive behavior of VDP structures on (100) silicon plane has been studied. In particular, the sensitivity of (100) silicon VDP structures to uniaxial stress has been explored theoretically and experimentally. Experimental data were obtained using four-point-bending tests, and typical results are presented. The observed VDP stress sensitivities were found to be much higher than those of their analogous resistor sensor counterparts. This result was confirmed through theoretical predictions and finite difference based anisotropic conduction simulations.