Fully flexible large-area MEMS-based triaxial force sensor compatible with flat panel display manufacturing

This work describes a fully flexible capacitive Micro-Electro-Mechanical-Systems (MEMS) based Large-Area (LA) triaxial force sensor, compatible with the Flat Panel Display (FPD) production. Thus, it is obtained by means of standard surface micromachining, unlike the reported other flexible sensor technologies, which are based on ad-hoc fabrication processes, that limit their large-scale manufacturing, area covering feature and flexibility. The triaxial force sensor is referred to as pixel. Its response is characterized in the mechanical and electrical domains. The effects of the fabrication-induced residual stresses as well as the applied external pressure and shear load are measured. The 3D Finite Element Method (FEM) model correctly captures the initial deflection due to the residual stresses. It properly simulates the pressure and shear behavior taking into account the contact between the embedded MEMS and the substrate. It represents a valuable tool to provide design guidelines for the MEMS optimization. The pixel normalized pressure sensitivity is equal to 0.0013 kPa^-1. While the shear one is 2.6 × 10^-3 kPa^-1. The sensitivity values of the presented device are higher than those reported for state-of-the-art capacitive triaxial force sensors. Potential sensing capability and scalability of the array design are preliminary proved. Referring to a 29 × 29 array with 1 cm² footprint, the predicted initial capacitance of each independent capacitor element is equal to 640 pF. The related pressure and differential shear sensitivities are 0.841 pF/kPa and 2.859 pF/kPa, respectively. The presented work describes a novel technology for highly sensitive flexible triaxial force sensors compatible with LA FPD cost-effective batch production.