Design and fabrication of a hybrid silicon three-axial force sensor for biomechanical applications

This paper presents the design and development of a silicon-based three-axial force sensor to be used in a flexible smart interface for biomechanical measurements. Normal and shear forces are detected by combining responses from four piezoresistors obtained by ion implantation in a high aspect-ratio cross-shape flexible element equipped with a 525 μm high silicon mesa. The mesa is obtained by a subtractive dry etching process of the whole handle layer of an SOI wafer. Piezoresistor size ranges between 6 and 10 μm in width, and between 30 and 50 μm in length. The sensor configuration follows a hybrid integration approach for interconnection and for future electronic circuitry system integration. The sensor ability to measure both normal and shear forces with high linearity (≅99%) and low hysteresis is demonstrated by means of tests performed by applying forces from 0 to 2 N. In this paper the packaging design is also presented and materials for flexible sensor array preliminary assembly are described.