A Novel CMOS-MEMS Tri-Axial Tactile Force Sensor Using Capacitive and Piezoresistive Sensing Mechanisms

This study proposes a novel design to implement a triaxial tactile force sensor, as shown in Fig. 1. The tactile force sensor is fabricated by TSMC standard CMOS process. The normal and shear forces sensing capabilities are achieved by three independent sensing components monolithically integrated on a single chip. Capacitive sensing membrane forms the normal force detection element and piezo-resistive bridges form the shear force detection elements. Merits of the design include (Fig. 2): (1) fully-clamped square-diaphragm array as the capacitive-type normal force sensing element: flexible only in out-of-plane direction (z-axis) to detect the normal load and avoid the cross-talk from shear forces; (2) clamped-clamped beam with Wheatstone bridge circuits as the piezo-resistive shear force sensing elements: flexible only in one in-plane direction (x-axis or y-axis) to detect the single axis share load, and the cross-talk from normal load is removed by the Wheatstone bridge circuits. Measurement results show the sensitivities of the proposed tri-axial tactile force sensor are 1.26 fF/N in z-axis, 2.043 mV/N in x-axis, 2.248 mV/N in y-axis and have less than 10% overall crosstalk.