Vertical integration of capacitive and piezo-resistive sensing units to enlarge the sensing range of CMOS-MEMS tactile sensor

This study presents a tactile sensor design to enlarge the sensing range by vertically integrated capacitive and piezo-resistive sensing units. The lower stiffness membrane with high sensitivity capacitance sensing electrodes is used to detect small force. To avoid the saturation of capacitive sensing, the higher stiffness cantilevers with piezo-resistive sensors are employed to detect larger force. Thus, sensing range of CMOS-MEMS tactile sensor is improved by the proposed two-stage sensing device. The presented design is implemented by the TSMC 0.18μm 1P6M standard CMOS process and in-house post-CMOS releasing. Measurement results indicate the capacitive sensing could detect loads ranging 0~0.03N (sensitivity is 1.8fF/mN) and the piezo-resistive sensing could detect loads ranging 0.05~0.5N (sensitivity is 9mV/N with 2 V input voltage).