Embossing-Controlled Hierarchical Structures in Cellulose-Derived Carbon Paper for Flexible Piezoresistive Pressure Sensing

Engineering three-dimensional (3D) microstructures in sensing layers is an effective strategy for improving the performance of flexible pressure sensors. However, most technologies for constructing 3D microstructures involve complex fabrication procedures and high costs, which hinder the commercialization of flexible electronics. Herein, inspired by embossing in papermaking, we developed a flexible piezoresistive pressure sensor based on carbonized embossed paper (CEP). Embossing followed by carbonization produced a hierarchical structure comprising a porous fibrous network and an array of surface micro-bumps. The spatial frequency and geometry of the micro-bump array were adjusted using metal mesh molds with different mesh counts. The CEP-50 sensor exhibited a sensitivity of 70.14 kPa−1 over 0–0.2 kPa, a working range of 0–150 kPa, a response time of approximately 60 ms, and stable responses over 5000 loading–unloading cycles. The CEP-50 sensor exhibited a sensitivity of 70.14 kPa−1 over 0–0.2 kPa, a working range of 0–150 kPa, a response time of approximately 60 ms, a low detection limit of 1.5 Pa, and stable responses over 5000 loading–unloading cycles. An equivalent circuit and finite element analysis were used to develop a qualitative interpretation of the pressure-dependent electrical response. The sensor was further demonstrated for monitoring pulse, respiration, phonation, and body movements. This embossing-based fabrication approach provides a practical route for developing paper-based wearable pressure sensors.