Micro sensors with polymer membrane for accurate 3D force and displacement measurements

Piezoresistive micro sensors allow force and displacement measurements with high resolution. These sensors are used in micro probing systems for dimensional metrology, but they permit maximal deflections of 100 μm only. In this technical area, forces as small as possible are required to measure microstructures without leaving scratches on the probed surfaces. In this work, the silicon membrane is replaced by a polymer, which reduces the stiffness of the probing systems considerably and increases the maximal allowed deflections at the same time. Simultaneously, a high sensitivity is presupposed, so that the diameter of the probing tip used for coordinate measurements can be reduced. For its realization, dry film photoresists DuPont™ PerMX™ 3050 and 3020 have been utilized as a membrane material in two different sensor designs. In order to reach a high sensitivity, the first design features four cantilevers with piezoresistors which are integrated in a 50 μm thin membrane. The second design features strain gauges, which have been made of gold and structured on a 20 μm thin membrane. Consequently, this work aims to increase the robustness of the silicon sensor element by improving the mechanical properties of the membrane.