3D piezoresistive silicon microprobes with stacked suspensions for tailored mechanical anisotropies

Different kinds of piezoresistive microprobes based on silicon have been developed to enable measurement with high accuracies. However, the typical mechanical anisotropy of such systems leads to the slip of the tip, when probing inclined surfaces. Here, a novel microprobe design is presented, which can be tailored to provide a range of anisotropy or even a perfect isotropy. In the first approach, the microprobe is composed of two stacked silicon membranes. In the second approach, a stainless steel suspension in the form of a laser structured foil is stacked on a silicon membrane. Geometrical parameter studies were carried out by mechanical FEM simulations to determine their influence on the stiffnesses in all spatial directions and to predict anisotropies. Microsystems with selected geometries were fabricated and stacking was obtained through selective adhesive transfer and bonding on a wafer level. Prototypes with anisotropies between 3 and 0.4 were characterized confirming the simulations.