Micromechanical force sensors based on SU-8 resist

Abstract

This paper presents an innovative approach to develop highly sensitive 3D force sensors. In order to increase the probing sensitivity by using a material with low Young’s Modulus, a novel force sensor design based on SU-8 polymer is realized. Therefore, a low cost fabrication process is developed accompanied by design studies and an estimation of mechanical properties of the deforming elements. This paper will present the fabrication process as well as a distinguishing set of test results, analytical results, and simulations on the characterization of the presented SU-8 force sensor. The novel SU-8 design consists of an SU-8 boss-membrane with integrated piezoresistive elements. The SU-8 membranes are structured using photolithography. The SU-8 micromechanical structures are characterized to determine film stresses, bending stiffness, displacement of the stylus, and breaking points. Included in these tests are measurement of the stress behavior at different process steps and simulation of stress distribution in the membrane at different directions of loading. In addition a comparative analytical investigation of the structures is carried out particularly with regard to the displacement of the stylus.