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 × 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/μm and 0.27–0.48 mN/μm 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.