Polymer-based flexible capacitive sensor for three-axial force measurements

We have developed a flexible-substrate-based three-axial force sensor, composed of finger-shaped electrode capacitors, whose operation is based on the measurement of a capacitance change induced upon applying a three-axial load. The electrode design supports high sensitivity to shear forces. An overall flexibility of the sensor and elasticity of the capacitor's dielectric is obtained by integrating three polymers in the sensor's technology process, namely polyimide, parylene-C, and polydimethylsiloxane, combined with standard metallization processes. We have theoretically modeled the sensor's capacitance and its three-axial force sensitivity. The unit capacitors have static capacitances in the range of 20 pF. The electro-mechanical characterization of the capacitors reveals in the normal direction a sensitivity S-z = 0.024 kPa(-1) for pressures <10 kPa, whereas for higher pressures the measured sensitivity S-z = 6.6 x 10(-4) kPa(-1). Typical measured shear force sensitivity S-x = 2.8 x 10(-4) kPa(-1). These values give our transducer high potential for use in skin-like sensing applications.