Research Progress in Nano Materials and Structural Designs for Flexible Piezoresistive Sensors

This review provides an overview of recent advances in the materials and structural design of flexible piezoresistive sensors, which are of significant interest as smart devices in the Fourth Industrial Revolution. Recent research has focused on addressing demand for a wide pressure range and high sensitivity for use in diverse applications. In terms of sensor materials, this review begins by introducing elastomers used for matrix and substrate, which provide exceptional conformability to curved surfaces and mechanical flexibility to withstand stretching and bending. They can also incorporate sensing materials in various forms of nanostructures capable of effectively transmitting electrical signals, exploiting the nanomaterial’s electrical properties and conductivity pathways formation mechanisms under pressure, which define the sensor’s characteristics. Additionally, this review explores structural design considerations, including different types of microstructures that can deform easily even under low pressure, enhancing sensor sensitivity, as well as hierarchical structures capable of gradual changes in contact area to provide a wide range of operating pressures. Moreover, the review discusses time- and cost-efficient microfabrication techniques to facilitate practical utilization of the device. This review then summarizes the applications of high-performance sensors in fields such as health monitoring, including pulse detection and motion tracking, robotics, and human-machine interaction involving components such as touch screens and keypads.