Simulation, fabrication and characterization of a 3D piezoresistive force sensor

In this contribution we report on a miniaturized bulk micro-machined three-axes piezoresistive force sensor. The force sensor consists of a full membrane with 16 conventional two terminal p-type diffused piezoresistors on the surface of the membrane. The die size of the chip is 6.5 mm x 6.5 mm. Piezoresistors with four different designs were placed on the membrane. Sensitivities were found to be in the range of 0.37-0.79 mV/(V mN) and 1.68-2.92 mV/(V mN) in Z-direction and X- or Y-direction, respectively. The stiffness of the measured microprobes in the range of 5-8 mN/mu m and 0.27-0.48 mN/mu m were obtained in vertical and lateral direction, respectively. Various single and twin membranes designs were simulated to calculate stiffness of the microprobe. The measurement results show a cross-axis sensitivity of <2.5% at full scale of 25 mN. (C) 2008 Elsevier B.V. All rights reserved.