A Highly Sensitive CMOS-MEMS Capacitive Tactile Sensor

This paper describes the design and characterization of a capacitive tactile sensor fabricated in a conventional CMOS process. To achieve a high capacitive sensitivity, an oscillator circuit is adopted to convert the pressure induced capacitive change to an output frequency shift. The complete post micromachining steps are performed on a CMOS die without resorting to a wafer process. The pressure-sensing membrane has a total size of 200 µ m × 200 µ m with an initial sensing capacitance of 153 fF. Experimental results show an initial frequency output at 48.96 MHz under no applied load. The total frequency shift is 13.5 MHz with a corresponding membrane displacement of 0.56 µ m and a capacitance change of 63 fF, averaging 0.21 MHz/fF. The measured force sensitivity is 26.1 kHz/µ N.