Enhancing Flexible Capacitive Sensor Performance through the Synergy of Thermally Expandable Microspheres and Carbon Nanotubes via 3D Direct Ink Writing

Abstract Flexible capacitive pressure sensors are crucial for applications in electronic skin, artificial intelligence, and wearable medical devices. Despite their potential, conventional sensors often suffer from low pressure sensitivity, particularly in high‐pressure environments, and complex microstructure construction methods. This study addresses these limitations by developing a novel flexible capacitive pressure sensor based on a composite dielectric layer consisting of carbon nanotubes (CNTs), thermally expandable microspheres (TEMs), and polydimethylsiloxane (PDMS), with a 3D direct ink writing (DIW) technology. The CNTs‐TEMs synergy modulates both mechanical and dielectric response in capacitive sensors, achieving a two‐order‐of‐magnitude enhancement in sensitivity compared to that of CNT‐only filler system. The groove‐like microstructure on the surface of the dielectric layer enables rapid and stable air expulsion to boost dielectric constant change and sensitivity under pressure. The proposed sensor exhibits a maximal sensitivity as high as 3.09 kPa ⁻¹ in the wide pressure range of 0–500 kPa, and a detection limit as low as 16.7 Pa. Furthermore, the sensor shows excellent pressure resolution of 0.3%, cycling stability over 40 000 cycles, and can accurately monitor various human activities, demonstrating its potential for applications in health monitoring and flexible electronics.