Novel MEMS stiffness sensor for force and elasticity measurements

This paper presents the design, mathematical model, fabrication and testing of a novel type of MEMS stiffness sensor. The proposed sensor can measure both contact force and the stiffness of the object under contact. The sensing concept utilizes multiple membranes with varying stiffnesses. The relative deflection of the sensing membranes can be measured to calculate the stiffness or elasticity of the targeted object. In order to validate the new sensing concept, MEMS capacitive sensors are fabricated using surface micromachining with each fabricated sensor having a 1 mm × 1 mm square active sensor area. Finally, the sensors are characterized by using them to touch polymers of different elastic stiffness values. The test results show that the fabricated sensor can discriminate elasticity variation of polymer specimens with a resolution of 0.1 MPa over a range of 0.7–1.2 MPa. The force sensing resolution is excellent and is as small as 0.2 mN over a force range of 0–0.5 N.