Rational Design of Ultrasensitive Pressure Sensors by Tailoring Microscopic Features

Wearable sensors are increasingly used in a wide range of applications such as tactile sensors and artificial skins for soft robotics, monitoring human motions for wellbeing and sports performance, and pressure control of compression garments for wound healing. In this work, an ultrasensitive resistive pressure sensor based on conductive polydimethylsiloxane (PDMS) thin films with different microstructures is presented. These microscopic features include micropyramids, micro-semispheres, and micro-semicylinders which are created by soft lithography replication of 3D printing templates. To enable piezoresistivity, a thin layer of carbon nanofibers (CNFs) is spray-coated on the textured PDMS film. The resistance changes of the three microstructure designs under compression loading show that the micro-semicylinder-based sensor has the highest sensitivity of -3.6 kPa(-1). Finite element modeling reveals that among the three designs, the micro-semicylinders show the largest change in contact area under the same pressure, consistent with the experimental results that the largest resistance change under the same pressure. This sensor is capable of detecting pressure as low as 1.0 Pa. This 3D printing technology is a promising fabrication technique to design microstructured piezoresistive layers, paving the way to tailor sensor performance by engineering their microstructures and to produce ultrasensitive pressure sensors at low cost.