Fully Flexible Large-Area MEMS-Based Triaxial Force Sensor Array Compatible With Flat Panel Display Manufacturing

This work describes the first fully flexible capacitive Micro-Electro-Mechanical-System (MEMS) based Large-Area (LA) triaxial force sensor array, compatible with the Flat Panel Display (FPD) production. Thus, it is obtained by means of standard surface micromachining, unlike the state-of-the-art flexible sensors, which are based on ad-hoc fabrication processes, that limit their large scale manufacturing, area covering feature and flexibility. The triaxial force sensor (referred to as pixel) response is characterized in the mechanical and electrical domain. The effect 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. Referring to 29 x 29 array with 1 cm2 footprint, each independent capacitor is characterized by an initial capacitance equal to 640 pF. The obtained pressure and shear sensitivities are respectively 1.934 pF/kPa and 2.859 pF/kPa. These result in 11 and 41 times greater than the state-of-the-art capacitive triaxial force sensors’ ones. The presented work describes a novel technology for highly sensitive flexible triaxial force sensors compatible with LA FPD cost-effective batch production.